Colibacillosis in poultry: unravelling the molecular basis of virulence of avian pathogenicEscherichia coliin their natural hosts

Evolutionary responses of Escherichia coli to phage pressure: insights into mucoidy and colanic acid overexpression

BACKGROUND

Antibiotic resistance is a major issue affecting all spheres of human activity, including agriculture. One significant example is the Avian Pathogenic Escherichia coli (APEC), a bacterium that infects poultry and leads to substantial economic losses in the farming industry. As antibiotics lose efficacity, bacteriophages (phages) -viruses that specifically target bacteria-are emerging as a promising alternative to antibiotics for treating and preventing bacterial infections. However, bacteria can develop resistance to phages through various mechanisms. Studying the coevolution between a phage and its host bacterium is important to gain insight into the phage's potential as a therapeutic agent. This study investigates the evolutionary responses of an APEC strain and a laboratory E. coli strain to a commercial phage originally isolated from APEC.

RESULTS

In most cases, phage resistance resulted in a significant increase in mucoidy. Genomic analysis revealed that this resistance consistently correlated with amino acid changes, particularly in proteins involved in colanic acid production, such as YrfF. Further investigation of a mutation found in the YrfF protein demonstrated that this mutation altered the protein's structure and its interaction with the membrane. Transcriptomic analysis confirmed that the genes involved in colanic acid production were significantly overexpressed. Although the strains possessed a CRISPR-Cas system, it did not contribute to phage resistance.

CONCLUSIONS

This study suggests that specific amino acid changes in key proteins may be a mechanism employed by E. coli, including APEC, to defend against phage infections.

Recombinant auto-bioluminescent Escherichia coli to monitor the progression of Escherichia coli infection in the embryonated chicken eggs

RESEARCH HIGHLIGHTS

Bioluminescence imaging enabled real-time, noninvasive tracking of a bioluminescent APEC infection in embryonated chicken eggs over time.Bioluminescence signals showed contrasting patterns for dead and surviving embryos.The ilux2-APEC showed a higher luminoscore than luxABCDE-APEC in inoculated embryonated chicken eggs.The in ovo bioluminescent signal from intact eggs effectively reflects the ex ovo signal following the take out of yolk and embryo.

Intestinal differential metabolite tryptophan from avian pathogenic Escherichia coli (APEC)-resistant and susceptible chickens alleviates APEC symptoms in chickens

To identify an effective antibiotic to combat avian pathogenic Escherichia coli (APEC), differential metabolites in the intestines of APEC-resistant and susceptible chickens were investigates. The effect of supplementing the diet of APEC-challenged chickens with the differential metabolite tryptophan was investigated. Tryptophan was identified as an important differential gut metabolite (APEC-resistant and susceptible chickens) using tryptophan-targeted metabolism detection. A total of 120 one-day-old chickens were divided into four groups: with and without 0.1 % tryptophan supplementation in the basal diet with and without APEC challenge. The APEC challenge test was conducted after an adaptation period of 8 days. The infection lasted 7 days, during which dead chickens were subjected to pathological autopsy, and the mortality rate was recorded. All chickens were slaughtered at the end of the infection test to calculate morbidity. Dietary supplementation with tryptophan did not significantly affect mortality in APEC-challenged chickens (P > 0.05) but significantly reduced their morbidity (P < 0.05). Dietary tryptophan supplementation reversed the elevated splenic gene expression of IL-6, TLR4, and NF-κB induced by the APEC challenge in chickens (P < 0.05). Tryptophan supplementation also alleviated the APEC-induced upregulation of the pro-inflammatory factors IL-6, IFN-γ, and IL-1β in the blood (P < 0.05). Simultaneously, dietary supplementation with tryptophan significantly increased glutathione peroxidase activity and total antioxidant capacity level in the blood of APEC-challenged chickens (P < 0.05). Thus, APEC challenging in chickens induced organ damage, up-regulated inflammation-related gene expression in the spleen, and increased the levels of inflammatory factors in the blood. Dietary supplementation with tryptophan inhibited the production of inflammatory factors, possibly through the TLR4/NF-κB signaling pathway and attenuated the morbidity and the inflammatory response caused by the APEC challenge.

Genomic features, antimicrobial resistance and pathogenicity assessment of Escherichia coli serotype O177:H51 strain JS01 isolated from a diseased chicken

BACKGROUND

Avian colibacillosis, caused by avian pathogenic Escherichia coli (APEC), remains one of the most significant bacterial diseases threatening global poultry production and causing substantial economic losses. The dominant serotypes of APEC regional diversity, complicating prevention and control efforts. Given the pathogen's importance, this study focused on the microbiological identification of an E. coli strain (JS01) isolated from diseased chickens on a poultry farm in China. Further analyses were conducted to characterize its antimicrobial resistance (AMR) phenotype and pathogenicity. To elucidate its multi-drug resistance and pathogenic mechanisms, whole-genome sequencing (WGS) of JS01 was performed, followed by functional gene annotation, sequence typing, and serotype analysis. Additionally, the genetic evolutionary characteristics of JS01 were investigated through comparative genomics and phylogenetic tree analysis.

RESULTS

Strain JS01 was identified as an ST155 E. coli of O177:H51 serotype, exhibiting multi-drug resistant and strong virulence. WGS revealed that JS01's genome consists of one chromosome and three plasmids, comprising 4,670 coding DNA sequences with a total length 5,089,394 bp. The genome harbored 64 AMR genes and 177 virulence factor (VF) genes. The AMR genes were primarily associated with defense mechanisms conferring antibiotic resistance, while the VF genes were linked to adhesins, motility, and effector systems. Comparative genomic analysis indicated that JS01 is closely related to GCA_900636075.1, ASM1038v1 and ASM3229062v1, which were isolated from different hosts.

CONCLUSION

This study isolated and identified the O177: H51 serotype E. coli strain JS01 from chickens. The findings of this study provide valuable insights into the serotype distribution, antibiotic resistance patterns, and virulence characteristics of APEC isolates from diseased chickens in China. These results lay a foundation for future research to more accurately assess the impact of colibacillosis on the poultry industry and to develop targeted control strategies.

Longitudinal study of avian pathogenic Escherichia coli (APEC) serogroups associated with disease in Georgia poultry using molecular serology and virulence gene analysis

Avian pathogenic Escherichia coli (APEC) is a significant cause of morbidity, mortality, and production loss to the poultry industry worldwide. Here, we characterized 569 E. coli isolates from avian-diagnosed colibacillosis cases from the state of Georgia, USA. In total, 339 isolates were assigned into 32 serogroups with the majority classifying as O78, O2, O25, O8, O1, O86, O18, and O15. Serogroup O25 was found to link with broilers, while broiler breeders were more often associated with serogroup O1 and pet/ hobby birds with serogroup O8. In addition, some serogroups (O1) were more prevalent in the summer and fall. Analysis for virulence-associated genes (VAGs) found 23.20% of isolates did not harbour any genes linked with the APEC pathotype, while ColV plasmid-associated genes (iroN, ompT, hlyF, iss, and aerJ) were frequently detected among most isolates (with 80-96% prevalence) and some of these genes were linked with serogroup. Phylogenetic analysis, classified isolates into phylogenetic groups B2 (34%), F (19%), A (15%), and G (9%). The phylogenetic group B2 isolates also harboured the highest number of VAGs. This study highlights that the current APEC-causing disease in birds in the State of Georgia has identified several emerging serogroups possessing several VAGs that could potentially lead to challenges in colibacillosis control.RESEARCH HIGHLIGHTSSeveral emerging APEC serogroups were observed in Georgia poultry populations.An association between APEC serogroups and bird type was observed.The prevalence of different APEC serogroups was influenced by season.A multiplex PCR assay targeting common serogroups of APEC in Georgia poultry was developed.

Serogrouping and Molecular Characterization of ESBL-Producing Avian Pathogenic Escherichia coli from Broilers and Turkeys with Colibacillosis in Algeria

Avian colibacillosis caused by avian pathogenic Escherichia coli (APEC) strains is a bacterial disease responsible for enormous economic losses in the poultry industry, due to high mortality rates in farms, antibiotic therapy costs, and seizures at slaughterhouses. The aim of this study was to characterize the serogroups and molecular features of extended spectrum β-lactamase (ESBL)-producing APEC isolates recovered from 248 liver samples of 215 broilers and 33 turkeys with colibacillosis lesions in northeast Algeria. For this, microbiological tests were carried out, according to the recommended standards: E. coli isolates were recovered using standard microbiological protocols, and identification was carried out by MALDI-TOF MS. Serogrouping was performed using a rapid agglutination slide and the antisera of three O somatic groups (O1, O2, O78). Antimicrobial susceptibility was determined by the disk diffusion method. PCR assays and sequencing were used to detect antimicrobial resistance genes, integrons, phylogrouping, and MLST. Conjugation experiments were also conducted to determine the transferability of the retrieved ESBL-encoding genes. Overall, 211 (85.1%) APEC isolates were collected (one per positive sample), and 164 (77.7%) of them were typable. The O2 and O1 serogroups were the most detected (46.1% in broiler typable isolates and 61.5% in turkey typable isolates). Seventeen APEC isolates were ESBL-producers and harbored the following genes (number of isolates): blaCTX-M-1 (14), blaCTX-M-15 (2), and blaSHV-12 (1). They belonged to phylogroups D (10 isolates), B1 (6 isolates), and B2 (1 isolate). The MLST of 13 ESBL producers revealed seven STs: ST23, ST38, ST48, ST117, ST131, ST1146, and ST5087. The ESBL-encoding genes were transferred by conjugation among 15 ESBL-producing isolates, and transconjugants acquired either the IncK or IncI1 plasmids. Concerted efforts from all poultry actors are needed to establish surveillance monitoring strategies to mitigate the spread of ESBL-producing isolates implicated in avian colibacillosis.

A rapid detection of Avian Pathogenic Escherichia coli (APEC) strains based on minimal number of virulence markers identified by whole genome sequencing

BACKGROUND

Colibacillosis is an important epidemiological and economic issue in poultry farming and breeding. A common problem with avian pathogenic Escherichia coli strains (APEC) that cause this disease is a lack of an uniform identification system, resulting from a variety of serotypes, phylogenetic groups, sequence types and combinations of virulence factors. There are no clearly defined features that can be associated with pathogenicity. Therefore, without precise identification of pathogenic strains and differentiation from commensal strains, there is no possibility of appropriate selection of targeted therapy. The widespread use of whole genome sequencing (WGS) in recent years creates new possibilities in diagnostics. Therefore, the purpose of this study was to select features defining the APEC pathotype, based on next generation sequencing (NGS), and design a diagnostic test based on selected factors.

RESULTS

A PCR diagnostic test is proposed. Three predictors of virulence were chosen according to in silico analysis: two virulence genes: iroC and hlyF, as well as one molecular marker of O78 serotype (wzx-O-antigen flippase of the O78 serotype). A choice of markers was supported by a chicken embryo model.

CONCLUSIONS

Whole genome sequencing of E. coli genomes allowed for the development of a rapid diagnostic method identifying pathogenic strains for poultry: APEC. The developed test can support field observations connected with the strain isolation source and clinical symptoms of the disease.

Liver transcriptome response to avian pathogenic Escherichia coli infection in broilers with corticosterone treatment

Avian pathogenic Escherichia coli (APEC) infection has high morbidity and mortality, and multiple stressors encountered during rearing place poultry in a state of stress. However, research on how poultry cope with APEC infection under stress situation is still limited. In this study, we established a broiler stress model by corticosterone (CORT) administration subcutaneously for 7 consecutive days, followed by APEC challenge intramuscularly. CORT treatment significantly reduced body weight (BW) and average daily gain (ADG) while increasing feed conversion ratio (FCR) (P < 0.01). APEC infection significantly decreased ADG (P < 0.01). CORT treatment and APEC infection elevated plasma corticosterone and heterophil to lymphocyte (H/L) ratio (P < 0.05). Additionally, plasma aspartate aminotransferase (AST), AST to alanine aminotransferase (AST/ALT) ratio, and lactate dehydrogenase (LDH) levels increased significantly (P < 0.01). Histopathological analysis revealed structural damage of liver, indicating that CORT treatment and APEC infection induced liver injury. However, CORT pretreatment broilers exhibited a milder histopathological lesions and significantly lower AST, ALT, and LDH levels (P < 0.05) compared to APEC infection alone. CORT treatment and APEC infection increased plasma levels of lysozyme (LZM), total protein (TP), and globulin (GLOB) (P < 0.05), while CORT pretreatment further elevating their concentrations compared to APEC infection alone, suggesting an enhanced innate immune response. Liver transcriptomic analysis identified 768, 335, and 567 differentially expressed genes (DEGs) following CORT, APEC, or both treatments, respectively, enriched in cytokine-cytokine receptor interaction, PPAR signaling pathway, Toll-like receptor signaling pathway, MAPK signaling pathway, steroid hormone biosynthesis pathway, arachidonic acid metabolism, and phagosome pathway, etc., indicating that CORT treatment regulates lipid metabolism and immunity, while APEC infection induces inflammation and disrupts lipid metabolism. Notably, CORT pretreatment may mitigate APEC induced liver injury by enhancing phagosome function. Moreover, glucocorticoid receptor (GR) may regulate DEGs expressions, thus affected broilers response to CORT, APEC, or both treatments. These results suggest that CORT treatment, APEC infection, or both significantly affect the growth performance, immune response and liver function of broilers, while lipid metabolism may play a crucial role.

Chlorogenic acid mitigates avian pathogenic Escherichia coli-induced intestinal barrier damage in broiler chickens via anti-inflammatory and antioxidant effects: CHLOROGENIC ACID AND BROILER CHICKENS

This study was conducted to investigate the protective effects of chlorogenic acid (CGA) on intestinal health in broilers challenged with avian pathogenic Escherichia coli (APEC). One hundred and eighty one-day-old male broiler chicks were divided into three groups with six replicates of ten chicks each for a 21-day trial. The birds in the control and APEC groups were fed a basal diet, while birds in the CGA-treated group received a basal diet supplemented with 1000 mg/kg of CGA. At 14 days, birds in the APEC and CGA groups were administered with an APEC suspension Compared with the APEC group, CGA incorporation decreased mortality and cecal Escherichia coli colonies in bacterially challenged broilers (P < 0.05). Additionally, CGA reduced the relative weight of the heart, liver, kidney, gizzard, proventriculus, and intestine, as well as serum triglyceride level and alanine aminotransferase activity in APEC-challenged broilers (P < 0.05). Supplementing CGA reduced the concentrations of interferon-γ, tumor necrosis factor-α, interleukin-1β, and/or interleukin-6 in serum, duodenum, jejunum, and/or ileum in APEC-challenged broilers presumably through the inactivation of the toll-like receptor 4/myeloid differentiation factor 88 pathway (P < 0.05). CGA administration reduced serum diamine oxidase activity and d-lactate and endotoxin concentrations, but increased the ratio between villus height and crypt depth in duodenum and jejunum of APEC-infected chickens, accompanied by the restored intestinal expression of tight junction proteins (claudin-1, claudin-2, occludin, and zonula occludens-1) and genes involved in apoptosis (B cell lymphoma-2 associated X protein, B cell lymphoma-2, and cysteine-requiring aspartate protease 9) (P < 0.05). Additionally, CGA increased superoxide dismutase, glutathione peroxidase, and catalase activities, and glutathione levels in serum and intestinal mucosa, but inhibited the accumulation of intestinal malondialdehyde in APEC-challenged broilers possibly via activating the nuclear factor-erythroid 2-related factor-2/heme oxygenase-1 pathway (P < 0.05). The results suggested that CGA alleviated APEC-induced intestinal damage in broilers by inhibiting inflammation and oxidative stress. However, its potential application in practical poultry production is contingent upon both its efficacy and cost-effectiveness.

Escherichia coli in Brazilian Poultry Fecal Samples: Co-Carriage of Fosfomycin and ESBL Resistance

Background/Objectives: Fosfomycin, a critically important antibiotic, is widely used to treat urinary tract infections (UTIs) caused by multidrug-resistant (MDR) Escherichia coli, particularly those producing extended-spectrum β-lactamases (ESBLs). However, its increasing use in livestock has raised concerns about resistance development and global dissemination. This study investigated fosfomycin resistance in E. coli isolates from 400 fecal samples collected at Brazilian broiler farms. Methods: The samples were tested for their minimum inhibitory concentration (MIC), screened with PCR for specific resistance genes, and selected isolated were whole genome sequenced. Results: Phenotypic resistance to fosfomycin was detected in 19% (75/400) of the isolates, while the fosA3 gene, encoding enzymatic resistance, was identified in 4% (16/400) via PCR screening. Long-read sequencing of seven fosA3-positive isolates revealed the presence of fosA3 on IncFII and IncX plasmids, often co-located with blaCTX-M-55 within a conserved IS26-flanked transposon. Comparative genomic analysis of 133,541 global E. coli genomes from EnteroBase showed that 35% harbored similar transposon structures, with 2% carrying fosA3. These fosA3-positive isolates were significantly associated with South America and exhibited high co-carriage of ESBL genes, particularly in environmental and poultry-associated isolates. Phylogenetic analysis demonstrated no clustering by host or geographic origin, highlighting the global dissemination of these resistance determinants. Conclusions: Our findings emphasize the role of poultry production in the spread of fosfomycin and ESBL resistance, driven by transmissible plasmids and co-selection with third-generation cephalosporins. Improved antimicrobial stewardship, surveillance programs, and alternative management strategies are urgently needed to mitigate the dissemination of resistance and preserve fosfomycin's efficacy in human medicine.

An insight into newly emerging avian pathogenic E. coli serogroups, biofilm formation, ESBLs and integron detection and in vivo pathogenicity in chicken

Bacterial diseases alone or in combination with other pathogens lead to significant economic losses in poultry globally including India. One of these diseases is avian colibacillosis which is caused by avian pathogenic Escherichia coli (APEC). The present study sought to isolate and characterize using in vivo and in vitro assays E. coli recovered from poultry diagnosed with colibacillosis. A total of 55 E. coli isolates were recovered from tissues of 55 broiler flocks affected with colibacillosis by using standard microbiological techniques, Vitek 2 Compact system and polymerase chain reaction. Out of 55 E. coli isolates, 50 (90.9 %) were characterized as APEC by multiplex PCR using a set of five virulence genes. On serotyping, 16 (32 %) APEC isolates were serogrouped as O26 followed by O98 (28 %), O120 (14 %), O11 (12 %), O135 (8 %) and O17 (4 %). The antimicrobial susceptibility testing of E. coli isolates revealed high antibiotic resistance against imipenem, tetracycline, ciprofloxacin and levofloxacin (96 % each). Interestingly all the 50 suspect APEC isolates were found to be multiple drug resistant (MDR) and the antimicrobial profiling indicated that these isolates could be classified into 38 resistotypes. Moreover, 10 (20 %) isolates were ESBL producers as per phenotypic characterization using combined disk diffusion test. On genotypic characterization of ESBLs, 31 (62 %) isolates were found positive for the blaTEM gene, whereas, 34 (68 %) isolates carried intI1 gene. On assessment for biofilm formation at 72 h incubation, thirteen (26 %) isolates were found to be strong biofilm producers, whereas nine (18 %) and twenty-eight (56 %) isolates were moderate and weak biofilm producers, respectively. Later, the LD50 of one MDR and strong biofilm producing isolate (APEC-P02) was calculated by in vivo oral challenge study in day old broiler chicks. The findings of this study demonstrated that LD50 of APEC-P02 isolate was 1.12 × 108 CFU/ml. The unexpectedly high prevalence of O11, O126, O98, O120 and O135 isolates suggest that there may be emergent serogroups causing colibacillosis in India. The current oral challenge study seems to be the first of its kind in India to estimate the LD50 of a multidrug resistant biofilm producer APEC isolate in day-old chicks.

When E. coli strikes: a necropsy analysis of a juvenile giraffe's fatal infection

BACKGROUND

As bacterial infections pose a major health risk to captive populations, disease prevention and management play a crucial role in the ex situ conservation of giraffes (Giraffa camelopardalis). This study describes the case of a giraffe that developed septicemia after an umbilical cord infection caused by Escherichia coli. To our knowledge, pathological changes in diseased giraffes caused by E. coli, which is an opportunistic pathogenic organism, have not been reported. This is the first report presenting an analysis of necropsies and subsequent microbiological investigations.

CASE PRESENTATION

The baby giraffe's mother died shortly after birth, so it had to be fed milk powder. The giraffe was healthy at first but developed symptoms like depression, loss of appetite, and lameness at 8 days old. At 14 days of age, the juvenile giraffe showed astasia and gradually died, with a disease course of 7 days. Postmortem examination revealed opisthotonus and navel swelling. Serofibrinous arthritis, serofibrinous necrotizing inflammation of periarticular soft tissue, serous omphalitis, and severe adventitia hemorrhage of the umbilical artery were observed. Severe serofibrinous pericarditis, pleuritis, and peritonitis were also observed. The interstitium of the pulmonary lobule widened because it was filled with a pale yellow translucent gelatinous exudate. Histopathologically, the calf had diffuse serous interstitial pneumonia, serous necrotizing umbilical arteritis, degenerative hepatitis with mild fibrosis, degenerative nephritis, hemorrhagic lymphadenitis, necrotizing enteritis, and necrotizing thyroiditis. Blue-stained clumps of bacteria of varying sizes and neutrophil infiltration were scattered or diffused in the interstitial connective tissue and edematous serosa of all tissues and organs, as well as in small vessels and lymphatic vessels, which were filled with many neutrophils (lymphatic spread). Single gram-negative Escherichia coli were cultured from all tissues of the animal. Polymerase chain reaction results of 16S rRNA of the isolated Escherichia coli had 99.79% homology to KJB03889.1.

CONCLUSIONS

The gross, histopathologic, microscopic, and polymerase chain reaction sequencing features reported in a juvenile giraffe were consistent with colibacillosis, which is a rare disease of giraffes. The gross, histopathologic, microscopic, and polymerase chain reaction sequencing features reported in a juvenile giraffe. This case serves as a paradigmatic illustration of a giraffe suffering from neglect and inadequate treatment, leading to severe consequences. In instances of giraffe Escherichia coli septicemia, it is imperative to thoroughly assess for underlying diseases, particularly in the absence of obvious predisposing factors. The rise of multidrug resistant organisms has constrained the efficacy of empirical antibiotic treatment, highlighting the importance of promptly conducting culture and sensitivity testing and employing antibiotic therapy guided by susceptibility results.

Assessment of antibiotic resistance and virulence in Escherichia coli strains isolated from poultry in Spain

Colibacillosis is a disease caused by avian pathogenic Escherichia coli (APEC) isolates which results in significant morbidity and mortality in poultry, as well as in economic loses. In order to identify APEC strains in a population of 898 E. coli isolates from poultry samples collected from different avian flocks located in the Valencian Region, Spain, we analysed the most significantly related to highly-pathogenic colibacillosis virulence-associated genes (VAGs) (hlyF, iroN, iss, iutA and ompT) by multiplex real-time polymerase chain reaction (RT-PCR). Results from this study showed that 59.5 % of the strains were identified as APEC by the expression of the five VAGs. In addition, both phenotypic and genotypic resistances to the last-resort antibiotic colistin in the same population were detected through either antimicrobial susceptibility tests or RT-PCR targeting mcr-1 and mcr-2 genes. An expected low frequency of colistin-resistant E. coli strains was detected as well as a low but noteworthy proportion of 3.3 % extremely-drug resistant strains, which encourages to still reducing the use of antibiotics in animals and humans to prevent the transmission of antimicrobial resistances among them.

Integrated Transcriptome Analysis Reveals the Lung miRNA-mRNA Regulatory Network Associated with Avian Pathogenic E. coli Infection

Avian pathogenic E. coli (APEC), one of the most common pathogens, can cause localized or systemic infections and lead to significant economic losses in the poultry industry annually. Recently, evidence suggests that microRNAs (miRNAs) play important roles in the host immune response to bacterial infection by targeting mRNAs. However, few studies have examined the immune mechanisms of miRNAs and mRNAs in chicken lungs following APEC infection. Herein, hematoxylin-eosin staining and qRT-PCR were employed to investigate APEC-induced lung inflammation in chickens. RNAseq was used to identify the miRNAs and mRNAs expression profile between the APEC infection group (APEC) vs. the Control group (Control). The results show that APEC can induce lung lesions in chickens and increase the expression levels of inflammatory cytokines (IL1β, IL8, IL6, and TNFα). High-quality sequencing data were obtained, of which more than 93% of the reads can be mapped to the chicken genome. A total of 22 differentially expressed (DE) miRNAs and 608 DE mRNAs were detected in the APEC vs. the Control. Remarkably, 23 regulatory pairs of miRNA-mRNA interactions were identified in chicken lungs upon APEC infection. Further validation revealed that gga-miR-214 could directly target the RAB37 gene upon APEC infection to modulate the expression of inflammatory cytokine response. This study provides new insights into the host immune response to APEC infection.

Epidemiological investigation and drug resistance analysis of avian pathogenic Escherichia coli (APEC) of Wenchang chickens in Hainan, China

RESEARCH HIGHLIGHTS

Type O8 is the most prevalent serotype of APEC isolated from Wenchang chicken embryos (Hainan, China).The isolates were more than 90% resistant to erythromycin, amoxicillin, ampicillin, and tetracycline.19.2% of the isolates were multi-resistant to more than 14 antibiotics.APEC of the same serotype isolated from Hainan Wenchang embryos have close relationships in the evolutionary tree of the core genome.

Avian pathogenic Escherichia coli alters complement gene expression in chicken erythrocytes

1. Avian Escherichia coli (E. coli) causes significant losses in livestock by inducing morbidity and mortality. Erythrocytes, the most abundant in blood, possess dual functions of oxygen transportation and immune regulation. In recent years, the interaction between erythrocytes and the complement system has gradually become a focal point of study. However, the transcription dynamics of the complement system in chicken erythrocytes post-E. coli invasion remains unclear.2. In this study, chicken erythrocytes and E. coli were co-cultured for 0.25-2 h to assess adhesion, analysed by indirect immunofluorescence (IIF) and scanning electron microscopy (SEM). Quantitative real-time PCR (qRT-PCR) examined differential expression of complement genes (CD93, C1q, C1s, C2, C3, C3AR1, C4, C4A, C5, C5AR1, C6, C7, C8G, CFI, MBL) in vitro using erythrocytes at 0.25-2 h and in vivo using chicks at 1, 3 and 7 d post-E. coli infection.3. E. coli adheres to chicken erythrocytes, as observed using IF and SEM. Gene expression analysis revealed early downregulation of C4, C4A, MBL and late upregulation of CD93, C1q, C1s, C3, C3AR1, C5AR1, C6, with C5, C7, C8G downregulated at 7 dpi. C2 expression varied at each time point.4. This study first showed E. coli adhering to erythrocytes, which activated complement genes rapidly. In vivo recovery from chickens with colibacillosis favours classical pathway activation, while lectin pathway may be inhibited, suggesting early immune down-regulation.

Avian pathogenic Escherichia coli: Epidemiology, virulence and pathogenesis, diagnosis, pathophysiology, transmission, vaccination, and control

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in poultry; this type of bacteria is an extraintestinal pathogen E. coli. Unlike other E. coli pathogen groups, the characteristics of APECs cannot be identified by a single group. Serotyping and biotyping are frequently performed for isolates found in colibacillosis infections. The establishment, transmission, and persistence of this pathogenic strain in chicken populations are determined by the intricate interactions of multiple elements that make up the epidemiology of APEC. APEC employs many virulence and pathogenesis factors or mechanisms to infect chickens with colibacillosis. These factors include invasives, protectins, adhesins, iron acquisition, and toxins. In addition, the pathogenicity of APEC strains can be evaluated in 2-4 week-old chicks. The impact of unfavorable environmental conditions has also been documented, despite direct contact being demonstrated to be a significant element in transmission in APEC. Chickens are immunized against colibacillosis using a variety of vaccines. Nevertheless, commercially available vaccinations do not offer sufficient immunity to protect birds from APEC strains. Hatching egg contamination is one of the main ways that APECs spread throughout chicken flocks. Farmers also need to be mindful of storing discarded materials near the manure-watering area, removing them when necessary, and replacing wet materials with dry materials when needed. This review aimed to explain the characteristics, epidemiology, virulence, pathogenesis, diagnosis, pathophysiology, transmission, vaccination, and control of APEC.

Prevalence and molecular characterization of ESBL-producing Escherichia coli isolated from broiler chicken and their respective farms environment in Malaysia

BACKGROUND

Extended spectrum beta-lactamase-producing Escherichia coli (ESBL-EC) is an increasing public health threat. This study aimed to determine the prevalence and characterization of ESBL-producing Escherichia coli (E. coli) isolated from broiler chicken and their farm environment, in Kelantan Malaysia.

METHODS

Escherichia coli was isolated from 453 collected samples, including 210 cloacal swabs and 243 environmental samples. The antimicrobial susceptibility profile of the E. coli isolates was assessed for sixteen antibiotics using the disc diffusion method. The E. coli isolates were evaluated for phenotypic ESBL production using modified double disc synergy. After extraction of genomic DNA, ESBL resistance genes, phylogenetic group, and virulence genes were detected by PCR using appropriate primers. ESBL genes were further confirmed by sequencing. The molecular typing of E. coli strains was determined by Multilocus Sequence Typing (MLST).

RESULTS

A total of 93.8% (425/453) E. coli were isolated from the collected samples. Out of 334 E. coli isolates screened, 14.7% (49/334) were phenotypically ESBL producers. All the ESBL-EC were resistant to tetracycline, ciprofloxacin, and ampicillin. Thus, 100% of the ESBL-EC were multidrug resistant. Of the ESBL-EC 81.6% were positive for at least one ESBL encoding gene. The most prevalent ESBL gene detected was blaTEM (77.6%; 38/49) followed by blaCTX-M (32.7%; 16/49) and blaSHV (18.4%; 9/49). The majority of ESBL-EC belonged to phylogenic groups A followed by B1 accounting for 44.9% and 12.2%, respectively. The most frequently identified sequence types were ST10 (n = 3) and ST206 (n = 3). The most detected virulence genes in the E. coli isolates were astA (33.3%; 22/66) followed by iss (15.2%; 10/66).

CONCLUSIONS

Our results show both broiler chicken and their respective farms environment were reservoirs of multi-drug resistant ESBL-producing E. coli and ESBL resistance genes.

Development of High-Production Bacterial Biomimetic Vesicles for Inducing Mucosal Immunity Against Avian Pathogenic Escherichia coli

To evaluate the immunoprotective effect of bacterial biomimetic vesicles (BBVs) against avian pathogenic Escherichia coli (APEC), a ΔtolA J11 mutant strain was generated by deleting the tolA gene in the low pathogenic O78 serotype J11 strain. The total protein content of outer membrane vesicles (OMVs) derived from the ΔtolA J11 strain exhibited a sevenfold increase compared to the wild-type strain. Additionally, high-pressure homogenization technology was employed to produce BBVs, resulting in a sixfold increase in total protein content compared to spontaneously secreted OMVs from ΔtolA J11. The immunogenicity of both OMVs and BBVs was assessed through intranasal or intramuscular immunization in specific pathogen-free (SPF) chickens. Results demonstrated that intranasal immunization with OMVs or BBVs in chickens elicited specific IgY antibodies against APEC outer membrane proteins and specific sIgA antibodies in the nasal cavity and trachea, as well as a significant increase in the proliferation response of chicken peripheral blood lymphocytes. The bacterial load in the blood and various organs of the challenged chickens were significantly reduced, resulting in a 66.67% and 58.30% survival rate against a high pathogenic serotype O78 strain challenge, while the control group exhibited only a 16.67% survival rate. The intramuscular immunization with OMVs or BBVs in chickens only induced specific IgY antibodies, with a survival rate of only 33.33% for challenged chickens during the same period. Therefore, intranasal vaccination of the highly productive BBVs is capable of eliciting an immune response similar to that of OMVs and providing protection against APEC infection, thus offering innovative insights for the advancement of APEC vaccines.

Biosensors for Monitoring, Detecting, and Tracking Dissemination of Poultry-Borne Bacterial Pathogens Along the Poultry Value Chain: A Review

The poultry industry plays a crucial role in global food production, with chickens being the most widely consumed as a rich protein source. However, infectious diseases pose significant threats to poultry health, underscoring the need for rapid and accurate detection to enable timely intervention. In recent years, biosensors have emerged as essential tools to facilitate routine surveillance on poultry farms and rapid screening at slaughterhouses. These devices provide producers and veterinarians with timely information, thereby promoting proactive disease management. Biosensors have been miniaturized, and portable platforms allow for on-site testing, thereby enhancing biosecurity measures and bolstering disease surveillance networks throughout the poultry supply chain. Consequently, biosensors represent a transformative advancement in poultry disease management, offering rapid and precise detection capabilities that are vital for safeguarding poultry health and ensuring sustainable production systems. This section offers an overview of biosensors and their applications in detecting poultry diseases, with a particular emphasis on enteric pathogens.

Immune modulation and cecal microbiome changes in broilers fed with fenugreek seeds and Bacillus-based probiotics

Intensive broiler production systems face challenges like enteric diseases, impacting global food security. Strategies to enhance broiler immunity and gut health, particularly amidst antibiotic growth promoter restrictions, are crucial. The present study investigated the combined effects of fenugreek seeds (FS) and Bacillus-based direct-fed microbials (DFM) on immune-related gene expression in the ileum and alteration of microbial population in the cecum of broiler. The study involved 160 Ross 308 broiler chicks, which were divided into four groups consisting of 5 replicates, each containing eight birds. The chicks were grown for a period of 42 d, during which they had ad libitum access to feed and water. Dietary treatments were: Control (basal diet), FS5 (basal + 5g/kg fenugreek seeds), FS5DFM (basal + 5g/kg fenugreek seeds + 0.1g/kg Bacillus-based DFM), and DFM (basal + 0.1g/kg Bacillus-based DFM). Ileum tissue and cecal contents were collected on d 42 for gene expression and gut microbiome analysis. Ileal gene expression analysis revealed the downregulation of IL-6, IL-8L2, CASP6, PTGS2, and IRF7 in both FSs and DFMs groups compared to the control, suggesting individual immunomodulatory effects. However, avian β-defensin genes exhibited complex regulation, highlighting the need for further investigation. Cecal microbiome diversity remained stable, with subtle shifts in specific taxa influenced by FSs and DFMs. Interestingly, the combination of the FSs and DFMs uniquely impacted specific taxa, including Clostridiales vadin BB60. These findings suggest that both FSs and DFMs demonstrated potential for improving broiler immunity through inflammation reduction. The combination of FSs and DFMs offers a synergistic effect in immune modulation and specific microbial modulation, warranting further investigation with pathogen challenge models for comprehensive understanding.

Antibiotic Resistance and Virulence Gene Patterns Associated with Multi Drug Resistant Avian Pathogenic Escherichia coli (APEC) Isolated from Broiler Chickens in India

In the present study, a total of 102 samples were collected from chickens of different flocks, died due to suspected colibacillosis. Bacteriological and PCR methods were applied to detect avian pathogenic Escherichia coli (APEC). Phenotypic antimicrobial resistance (AMR) was determined by disk diffusion method. Extended spectrum beta lactamases (ESBL) detection was carried out via PCR by targeting blaTEM, blaSHV, blaOXA, and blaCTX-M groups 1, 2, and 9. Genes of eight virulence factors and class I integrons were also detected by PCR using gene specific primers. Culture, microscopic, biochemical tests and PCR recognised 69/102 (67.64%) samples as E. coli. Phenotypic AST revealed higher resistance against fluoroquinolone antibiotics, i.e., enrofloxacin (72.46%), levofloxacin (69.56%) & ciprofloxacin (66.66%), followed by amoxyclav (63.77%) and tetracycline (59.42%). Six isolates were found as pan-drug-resistant E. coli. A total of 48 (69.56%) and 7 (10.14%) isolates were positive for the presence of blaTEM and blaCTX-M-G9 genes, respectively, whereas 2 (2.90%) isolates each were found positive for blaSHV, blaOXA, and blaCTX-M-G1 genes. Among APEC associated virulence genes, iss (79.71%) was the most predominant, followed by tsh (50.72%), ast (30.43%), cvaf (26.08%), pap (23.18%), vat (8.69%) and stx-1 (1.44%). Thirty-two isolates harboured class I integrons, either with or without ESBL genes. Conclusively, the isolates under study showed pan and multiple-drug resistance, specifically against fluoroquinolone drugs. ESBL production was mediated principally through bla TEM and blaCTX-M-G9. Multiple virulence factors, toxins, and carriage & spread factor render these as zoonotically potential pathogens for humans.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-023-01132-2.

Dietary supplementation with a silicate clay mineral (palygorskite) alleviates inflammatory responses and intestinal barrier damage in broiler chickens challenged with Escherichia coli

This experiment aimed to explore the protective effects of dietary palygorskite (Pal) supplementation on inflammatory responses and intestinal barrier function of broiler chickens challenged with Escherichia coli (E. coli). A 2 × 2 factorial arrangement was designed to assess the effects of Pal administration (0 or 5 g/kg of feed) and E. coli challenge (E. coli or bacterial culture medium) on broilers in a 21-d feeding trial. Birds were randomly assigned into one of the 4 groups, and each group had 8 replicates with ten birds each. The challenged chickens were orally gavaged with E. coli suspended in Luria-Bertani broth on 14 d of age, while unchallenged birds were administrated with an equivalent amount of culture medium. The sampling was performed at 21 d of age. Compared with the normal birds, an oral E. coli challenge reduced final body weight, and decreased feed intake, weight gain, and feed efficiency during the challenge period (P < 0.05). E. coli challenge promoted colonization of E. coli in cecal content and their translocation to internal organs (heart, liver, and spleen) (P < 0.05). E. coli infection also increased levels of pro-inflammatory cytokines in jejunum and ileum possibly through activating the toll-like receptor-4-mediated signaling pathway (P < 0.05). Moreover, E. coli administration increased intestinal mucosal permeability (higher serum D-lactate level and diamine oxidase activity, and lower intestinal mucosal disaccharidase activities), altered intestinal morphology, and downregulated the gene expression of intestinal tight junction proteins (P < 0.05). In contrast, Pal supplementation enhanced growth performance, inhibited colonization of E. coli, reduced intestinal inflammation, decreased intestinal permeability, restored intestinal morphology, and normalized the expression of genes responsible for inflammatory processes and maintenance of intestinal mucosal barrier (P < 0.05), and most of these beneficial effects resulting from Pal administration were independent of bacterial challenge. The results indicated dietary Pal incorporation was effective in improving growth performance and alleviating inflammation and intestinal mucosal barrier damage in broilers challenged with E. coli.

Molecular detection of avian pathogenic Escherichia coli (APEC) in broiler meat from retail meat shop

Avian pathogenic Escherichia coli (APEC) is a major bacterial pathogen responsible for the most widespread form of colibacillosis, resulting in substantial economic losses within the poultry sector and posing a potential public health risk. From July to September 2021, our study investigated the antibiotic resistance pattern of Escherichia coli (E. coli) and the presence of virulence-associated genes (iucD, iutA, iss, and ompT) linked to APEC using 105 broiler meat samples comprising liver, thigh, and breast muscle, in Chitwan, Nepal. E. coli was isolated and identified by culturing samples on MacConkey's agar, Eosin-methylene blue (EMB) agar and performing different biochemical tests. Antibiotic resistance patterns of E. coli were determined by the Kirby-Bauer disc diffusion method. Following the isolation of E. coli, the molecular detection of APEC was performed using conventional polymerase chain reaction (PCR). Out of the 105 samples analyzed, 61 (58.1 %) tested positive for E. coli. In antibiotic susceptibility test (AST), gentamicin and tetracycline exhibited the highest resistance rates, with 90.2 % and 67.2 %, respectively and 29.5 % of the E. coli isolates displayed multidrug-drug resistance. Out of 61 confirmed E. coli isolates, iutA was detected in 47 (77.0 %) samples, iucD in 46 (75.4 %), iss in 53 (86.8 %), and ompT in 39 (63.9 %) samples. This study reports the occurrence of MDR E. coli in meat samples, together with virulence genes associated with APEC which poses a public health threat. Continuous surveillance is vital for monitoring APEC transmission within poultry farms, coupled with efforts to raise awareness of food safety among consumers of broiler meat.

MiR-20a-5p Targeting the TGFBR2 Gene Regulates Inflammatory Response of Chicken Macrophages Infected with Avian Pathogenic E. coli

Avian pathogenic E. coli (APEC) causes localized and systemic infections and are a threat to human health. microRNAs (miRNAs) play critical roles in inflammation and immune regulation following pathogen invasion. However, the related regulatory mechanism remains unclear. This study aimed to elucidate the involvement of chicken microRNA-20a-5p (gga-miR-20a-5p) in host defense against APEC in chickens and the underlying mechanisms. We evaluated the expression levels of gga-miR-20a-5p in chicken tissues and cells and observed a significant decrease in expression following APEC infection. Dual luciferase reporter assays showed that gga-miR-20a-5p directly targeted transforming growth factor-beta receptor 2 (TGFBR2), specifically by binding to the 3'-untranslated region (3'UTR) of TGFBR2. Overexpression of gga-miR-20a-5p markedly reduced both the mRNA and protein levels of TGFBR2, whereas inhibition of gga-miR-20a-5p significantly increased expression. Mechanistic investigations revealed that overexpression of gga-miR-20a-5p also attenuated the expression levels of the pro-inflammatory cytokines IL8, TNFα, IL6, and IL1β, whereas inhibition of gga-miR-20a-5p had the opposite effects. Collectively, our findings suggest that gga-miR-20a-5p regulates the immune response during APEC infection by targeting TGFBR2, thereby suppressing inflammatory cytokine production. This study provides valuable insights into the role of gga-miR-20a-5p in the host defense against APEC.

Virulence-associated genes in faecal and clinical Escherichia coli isolates cultured from broiler chickens in Australia

A healthy chicken's intestinal flora harbours a rich reservoir of Escherichia coli as part of the commensal microbiota. However, some strains, known as avian pathogenic E. coli (APEC), carry specific virulence genes (VGs) that enable them to invade and cause extraintestinal infections such as avian colibacillosis. Although several VG combinations have been identified, the pathogenic mechanisms associated with APEC are ill-defined. The current study screened a subset of 88 E. coli isolates selected from 237 pre-existing isolates obtained from commercial poultry flocks in Australia. The 88 isolates were selected based on their enterobacterial repetitive intergenic consensus (ERIC) and antimicrobial resistance (AMR) profiles and included 29 E. coli isolates cultured from chickens with colibacillosis (referred to as clinical E. coli or CEC) and 59 faecal E. coli (FEC) isolates cultured from clinically healthy chickens. The isolates were screened for the presence of 35 previously reported VGs. Of these, 34 were identified, with iucA not being detected. VGs focG, hlyA and sfa/foc were only detected in FEC isolates. Eight VGs had a prevalence of 90% or above in the CEC isolates. Specifically, astA (100%); feoB (96.6%); iutA, iss, ompT, iroN and hlyF (all 93.1%); and vat (89.7%). The prevalence of these were significantly lower in FEC isolates (astA 79.7%, feoB 77.9%, iutA 52.5%, iss 45.8%, ompT 50.9%, iroN 37.3%, hlyF 50.9% and vat 42.4%). The odds ratios that each of these eight VGs were more likely to be associated with CEC than FEC ranged from 7.8 to 21.9. These eight VGs may be used to better define APEC and diagnostically detect APEC in Australia. Further investigations are needed to identify the roles of these VGs in pathogenicity.

Paeoniflorin protects chicken against APEC-induced acute lung injury by affecting the endocannabinoid system and inhibiting the PI3K/AKT and NF-κB signaling pathways

Avian pathogenic Escherichia coli (APEC) is the causative agent of chicken colibacillosis. Paeoniflorin, a natural ingredient extracted from Paeonia lactiflora, has a variety of pharmacological effects including anti-inflammatory and immunomodulatory. However, its effects and mechanism in APEC-induced acute lung injury (ALI) in chicken is not clear. The aim of this study was to investigate the protective effect of paeoniflorin on APEC-induced ALI and its possible mechanism. Paeoniflorin (25, 50, and 100 mg/kg) was administered by gavage for 5 d starting at 9 d of age and the chicken were infected with APEC by intraperitoneal injection at 12 d of age. The tissues were collected after APEC infection for 36 h for analysis. The results showed that paeoniflorin significantly alleviated the symptoms, increased the survival rate and body weight gain of APEC-infected chicken, and improved the histopathological damages, and reduced APEC loads in lung tissues. In addition, paeoniflorin restored the gene expression of ZO-1, Occludin and Claudin-3 during APEC infection. Moreover, paeoniflorin pretreatment significantly affected the endocannabinoid system (ECs) by increasing DAGL, decreasing MAGL, increasing secretion of 2-AG. Then, paeoniflorin significantly decreased the secretion of IL-1β, IL-6 and TNF-α in lung tissues, and decreased the mRNA expression of CXCL8, CXCL12, CCL1, CCL5, and CCL17. In addition, paeoniflorin significantly reduced the phosphorylation levels of PI3K, AKT, P65, and IκB. In summary, we found that paeoniflorin inhibited APEC-induced ALI, and its mechanism may be through affecting ECs and inhibiting the activation of PI3K/AKT and NF-κB signaling pathways, which provides a new idea for the prevention and treatment of chicken colibacillosis.

Reversal of gentamicin sulfate resistance in avian pathogenic Escherichia coli by matrine combined with berberine hydrochloride

In recent years, the evolution of antibiotic resistance has led to the inefficacy of several antibiotics, and the reverse of resistance was a novel method to solve this problem. We previously demonstrated that matrine (Mat) and berberine hydrochloride (Ber) had a synergistic effect against multidrug-resistant Escherichia coli (MDREC). This study aimed to demonstrate the effect of Mat combined with Ber in reversing the resistance of MDREC. The MDREC was sequenced passaged in the presence of Mat, Ber, and a combination of Mat and Ber, which did not affect its growth. The reverse rate was up to 39.67% after MDREC exposed to Mat + Ber for 15 days. The strain that reversed resistance was named drug resistance reversed E. coli (DRREC) and its resistance to ampicillin, streptomycin, gentamicin, and tetracycline was reversed. The MIC of Gentamicin Sulfate (GS) against DRREC decreased 128-fold to 0.63 µg/mL, and it was stable within 20 generations. Furthermore, the susceptible phenotype of DRREC remained stable within 20 generations, as well. The LD50 of DRREC for chickens was 8.69 × 109 CFU/mL. qRT-PCR assays revealed that the transcript levels of antibiotic-resistant genes and virulence genes in the DRREC strain were significantly lower than that in the MDREC strain (P < 0.05). In addition, GS decreased the death, decreased the bacterial loading in organs, alleviated the injury of the spleen and liver, and decreased the cytokine levels in the chickens infected by the DRREC strain. In contrast, the therapeutic effect of GS in chickens infected with MDREC was not as evident. These findings suggest that the combination of Mat and Ber has potential for reversing resistance to MDREC.

Gastrointestinal response to the early administration of antimicrobial agents in growing turkeys infected with Escherichia coli

This study investigated the effects of the early administration of enrofloxacin (E) or doxycycline (D) for the first 5 consecutive days of life, or the continuous administration of the coccidiostat monensin (M) throughout the rearing period on gastrointestinal function in turkeys infected with avian pathogenic Escherichia coli (APEC) in an early or later stage of rearing. Experiment 1 lasted 21 d, and turkeys in groups E, D, and M were infected with APEC on d 15. Experiment 2 lasted 56 d, and it had a factorial arrangement of treatments where birds in groups E, D, and M were infected with APEC on d 15 or d 50. In both experiments, control groups (C) consisted of infected and uninfected birds without antibiotic or coccidiostat administration. On d 21 (Experiment 1) and d 56 (Experiment 2), 8 birds from each subgroup were killed, and the ileal and cecal digesta were sampled to analyze the activity of bacterial enzymes and the concentrations of short-chain fatty acids (SCFA). The experimental treatments did not affect the final body weight or body weight gain of birds. Both experiments demonstrated that APEC contributed to an increase in ammonia levels of the cecal digesta (means from 2 experiments: 0.311 vs. 0.225 mg/g in uninfected birds) and ileal pH (6.79 vs. 6.00) and viscosity (2.43 vs. 1.83 mPa⋅s). Moreover, the E. coli challenge enhanced the extracellular activity of several cecal bacterial enzymes, especially in older turkeys infected with APEC in a later stage of life. The continuous administration of monensin throughout the rearing period resulted in a weaker gastrointestinal response in older birds, compared with the other 2 antibiotics administered for the first 5 d of life. The results of the study are inconclusive as both desirable and undesirable effects of preventive early short-term antibiotic therapy were observed in turkeys, including normalization of ileal viscosity and cecal ammonia concentration (positive effect), and disruption in cecal SCFA production (negative effect).

FdeC expression regulates motility and adhesion of the avian pathogenic Escherichia coli strain IMT5155

Adaptation of avian pathogenic E. coli (APEC) to changing host environments including virulence factors expression is vital for disease progression. FdeC is an autotransporter adhesin that plays a role in uropathogenic Escherichia coli (UPEC) adhesion to epithelial cells. Expression of fdeC is known to be regulated by environmental conditions in UPEC and Shiga toxin-producing E. coli (STEC). The observation in a previous study that an APEC strain IMT5155 in which the fdeC gene was disrupted by a transposon insertion resulted in elevated adhesion to chicken intestinal cells prompted us to further explore the role of fdeC in infection. We found that the fdeC gene prevalence and FdeC variant prevalence differed between APEC and nonpathogenic E. coli genomes. Expression of the fdeC gene was induced at host body temperature, an infection relevant condition. Disruption of fdeC resulted in greater adhesion to CHIC-8E11 cells and increased motility at 42 °C compared to wild type (WT) and higher expression of multiple transporter proteins that increased inorganic ion export. Increased motility may be related to increased inorganic ion export since this resulted in downregulation of YbjN, a protein known to supress motility. Inactivation of fdeC in APEC strain IMT5155 resulted in a weaker immune response in chickens compared to WT in experimental infections. Our findings suggest that FdeC is upregulated in the host and contributes to interactions with the host by down-modulating motility during colonization. A thorough understanding of the regulation and function of FdeC could provide novel insights into E. coli pathogenesis.

K1 capsule-dependent phage-driven evolution in Escherichia coli leading to phage resistance and biofilm production

AIMS

Understanding bacterial phage resistance mechanisms has implications for developing phage-based therapies. This study aimed to explore the development of phage resistance in Escherichia coli K1 isolates' to K1-ULINTec4, a K1-dependent bacteriophage.

METHODS AND RESULTS

Resistant colonies were isolated from two different strains (APEC 45 and C5), both previously exposed to K1-ULINTec4. Genome analysis and several parameters were assessed, including growth capacity, phage adsorption, phenotypic impact at capsular level, biofilm production, and virulence in the in vivo Galleria mellonella larvae model. One out of the six resistant isolates exhibited a significantly slower growth rate, suggesting the presence of a resistance mechanism altering its fitness. Comparative genomic analysis revealed insertion sequences in the region 2 of the kps gene cluster involved in the capsule biosynthesis. In addition, an immunoassay targeting the K1 capsule showed a very low positive reaction compared to the control. Nevertheless, microscopic images of resistant strains revealed the presence of capsules with a clustered organization of bacterial cells and biofilm assessment showed an increased biofilm production compared to the sensitive strains. In the G. mellonella model, larvae infected with phage-resistant isolates showed better survival rates than larvae infected with phage-sensitive strains.

CONCLUSIONS

A phage resistance mechanism was identified at the genomic level and had a negative impact on the K1 capsule production. The resistant isolates showed an increased biofilm production and a decreased virulence in vivo.

A systematic review and meta-analysis on the efficacy of vaccination against colibacillosis in broiler production

Colibacillosis, a disease caused by Escherichia coli in broiler chickens has serious implications on food safety, security, and economic sustainability. Antibiotics are required for treating the disease, while vaccination and biosecurity are used for its prevention. This systematic review and meta-analysis, conducted under the COST Action CA18217-European Network for Optimization of Veterinary Antimicrobial Treatment (ENOVAT), aimed to assess the efficacy of E. coli vaccination in broiler production and provide evidence-based recommendations. A comprehensive search of bibliographic databases, including, PubMed, CAB Abstracts, Web of Science and Agricola, yielded 2,722 articles. Following a defined protocol, 39 studies were selected for data extraction. Most of the studies were experimental infection trials, with only three field studies identified, underscoring the need for more field-based research. The selected studies reported various types of vaccines, including killed (n = 5), subunit (n = 8), outer membrane vesicles/protein-based (n = 4), live/live-attenuated (n = 16), and CpG oligodeoxynucleotides (ODN) (n = 6) vaccines. The risk of bias assessment revealed that a significant proportion of studies reporting mortality (92.3%) or feed conversion ratio (94.8%) as outcomes, had "unclear" regarding bias. The meta-analysis, focused on live-attenuated and CpG ODN vaccines, demonstrated a significant trend favoring both vaccination types in reducing mortality. However, the review also highlighted the challenges in reproducing colibacillosis in experimental setups, due to considerable variation in challenge models involving different routes of infection, predisposing factors, and challenge doses. This highlights the need for standardizing the challenge model to facilitate comparisons between studies and ensure consistent evaluation of vaccine candidates. While progress has been made in the development of E. coli vaccines for broilers, further research is needed to address concerns such as limited heterologous protection, practicability for application, evaluation of efficacy in field conditions and adoption of novel approaches.

The H9N2 avian influenza virus increases APEC adhesion to oviduct epithelia by viral NS1 protein-mediated activation of the TGF-β pathway

H9N2 avian influenza is a low-pathogenic avian influenza circulating in poultry and wild birds worldwide and frequently contributes to chicken salpingitis that is caused by avian pathogenic Escherichia coli (APEC), leading to huge economic losses and risks for food safety. Currently, how the H9N2 virus contributes to APEC infection and facilitates salpingitis remains elusive. In this study, in vitro chicken oviduct epithelial cell (COEC) model and in vivo studies were performed to investigate the role of H9N2 viruses on secondary APEC infection, and we identified that H9N2 virus enhances APEC infection both in vitro and in vivo. To understand the mechanisms behind this phenomenon, adhesive molecules on the cell surface facilitating APEC adhesion were checked, and we found that H9N2 virus could upregulate the expression of fibronectin, which promotes APEC adhesion onto COECs. We further investigated how fibronectin expression is regulated by H9N2 virus infection and revealed that transforming growth factor beta (TGF-β) signaling pathway is activated by the NS1 protein of the virus, thus regulating the expression of adhesive molecules. These new findings revealed the role of H9N2 virus in salpingitis co-infected with APEC and discovered the molecular mechanisms by which the H9N2 virus facilitates APEC infection, offering new insights to the etiology of salpingitis with viral-bacterial co-infections.IMPORTANCEH9N2 avian influenza virus (AIV) widely infects poultry and is sporadically reported in human infections. The infection in birds frequently causes secondary bacterial infections, resulting in severe symptoms like pneumonia and salpingitis. Currently, the mechanism that influenza A virus contributes to secondary bacterial infection remains elusive. Here we discovered that H9N2 virus infection promotes APEC infection and further explored the underlying molecular mechanisms. We found that fibronectin protein on the cell surface is vital for APEC adhesion and also showed that H9N2 viral protein NS1 increased the expression of fibronectin by activating the TGF-β signaling pathway. Our findings offer new information on how AIV infection promotes APEC secondary infection, providing potential targets for mitigating severe APEC infections induced by H9N2 avian influenza, and also give new insights on the mechanisms on how viruses promote secondary bacterial infections in animal and human diseases.

Risk factors associated with mcr-1 colistin-resistance gene in Escherichia coli broiler samples in northern Jordan

OBJECTIVES

The purpose of this study was to determine the prevalence of colistin-resistant Escherichia coli carrying mcr-1, and to identify risk factors associated with mcr gene-mediated resistance.

METHODS

In total, 385 cloacal samples were collected from 125 broiler farms and a questionnaire containing information about each farm was designed and filled.

RESULTS

Most of the antibiotics used in the disk diffusion method were highly resistant in all samples, with tetracycline and penicillin showing 100% and 99.7% resistance, respectively. Additionally, avian pathogenic E. coli (APEC) virulence genes frequency and percentage of APEC were identified, including sitA,iucC, and astA at 77%, 70.5%, and 62% respectively. In total, 214 of 360 isolates were positive for APEC (59.4%). Based on the minimum inhibitory (MIC) test, 58% of the isolates (n = 209 of 360) were resistant to colistin, with 39.7% displaying the mcr-1 gene. The statistical analysis of risk factors that influence colistin resistance prevalence revealed several significant factors, including commercial feed, farm management, sanitization, and antibiotic use. Irregular health checks for workers, non-dipping of feet before entering poultry houses, and the use of commercial poultry feeds all contributed to higher levels of colistin resistance as measured by MIC. On the other hand, doxycycline and commercial feed was 4 and 3.2 times more likely to occur based on the final logistic model of the mcr-1 gene, respectively.

CONCLUSION

Our results suggest that better biosecurity protocols should be implemented in poultry farms to reduce antibiotic-resistant bacteria. Additionally, antibiotics should be carefully monitored and used only when necessary.

Identification and Genomic Analyses of a Multidrug Resistant Avian Pathogenic Escherichia coli Coharboring mcr-1, bla TEM-176 and bla CTX-M-14 Genes

The emergence and transmission of the colistin-resistance gene mcr and extended-spectrum β-lactamase (ESBL) encoding genes pose a significant threat to global public health. In recent years, it has been reported that mcr-1 and ESBL genes can coexist in single bacteria strain. The objective of this study was to characterize a multidrug-resistant (MDR) avian pathogenic Escherichia coli (APEC) isolate carrying mcr and ESBL encoding genes in China. A total of 200 APEC isolates were collected for antimicrobial susceptibility testing by Kirby-Bauer (K-B) disk method. The MDR strain EC012 were then further analyzed for minimum inhibitory concentrations, antimicrobials resistance genes (ARGs) detection, conjugation, and whole-genome sequencing (WGS). Among all APEC isolates determined by K-B disk method, strain EC012 was resistant to almost all the antimicrobials, including polymyxin B, cefotaxime, and ceftazidime. Moreover, EC012 harbored ARGs mcr-1, bla TEM-176, and bla CTX-M-14. WGS analysis revealed that EC012 belonged to epidemic APEC serotype O1:H16 and multilocus sequence type ST295. EC012 consisted of one chromosome and six plasmids, encoding a broad ARGs. The bla CTX-M-14, mcr-1 or bla TEM-176 genes were located on conjugative plasmids pEC012-1 or pEC012-5, respectively. These plasmids were successfully transferred to transconjugants and resulted in the resistance to polymyxin B, cefotaxime, and ceftazidime. This study indicated that APEC was a potential reservoir of colistin-resistance gene mcr-1 and ESBL encoding genes, and highlighted the necessity for enhanced monitoring of ARGs dissemination among bacteria from different origins.

Genome-wide transcriptional profiling and functional analysis of long noncoding RNAs and mRNAs in chicken macrophages associated with the infection of avian pathogenic E. coli

BACKGROUND

Avian pathogenic E. coli (APEC) can cause localized or systemic infections, collectively known as avian colibacillosis, resulting in huge economic losses to poultry industry globally per year. In addition, increasing evidence indicates that long non-coding RNAs (lncRNAs) play a critical role in regulating host inflammation in response to bacterial infection. However, the role of lncRNAs in the host response to APEC infection remains unclear.

RESULTS

Here, we found 816 differentially expressed (DE) lncRNAs and 1,798 DE mRNAs in APEC infected chicken macrophages by RNAseq. The identified DE lncRNA-mRNAs were involved in Toll like receptor signaling pathway, VEGF signaling pathway, fatty acid metabolism, phosphatidylinositol signaling system, and other types of O-glycan biosynthesis. Furthermore, we found the novel lncRNA TCONS_00007391 as an important immune regulator in APEC infection was able to regulate the inflammatory response by directly targeting CD86.

CONCLUSION

These findings provided a better understanding of host response to APEC infection and also offered the potential drug targets for therapy development against APEC infection.

Use of Essential Oils to Counteract the Phenomena of Antimicrobial Resistance in Livestock Species

Antimicrobial resistance is an increasingly widespread phenomenon that is of particular concern because of the possible consequences in the years to come. The dynamics leading to the resistance of microbial strains are diverse, but certainly include the incorrect use of veterinary drugs both in terms of dosage and timing of administration. Moreover, the drug is often administered in the absence of a diagnosis. Many active ingredients in pharmaceutical formulations are, therefore, losing their efficacy. In this situation, it is imperative to seek alternative treatment solutions. Essential oils are mixtures of compounds with different pharmacological properties. They have been shown to possess the antibacterial, anti-parasitic, antiviral, and regulatory properties of numerous metabolic processes. The abundance of molecules they contain makes it difficult for treated microbial species to develop pharmacological resistance. Given their natural origin, they are environmentally friendly and show little or no toxicity to higher animals. There are several published studies on the use of essential oils as antimicrobials, but the present literature has not been adequately summarized in a manuscript. This review aims to shed light on the results achieved by the scientific community regarding the use of essential oils to treat the main agents of bacterial infection of veterinary interest in livestock. The Google Scholar, PubMed, SciELO, and SCOPUS databases were used for the search and selection of studies. The manuscript aims to lay the foundations for a new strategy of veterinary drug use that is more environmentally friendly and less prone to the emergence of drug resistance phenomena.

Antimicrobial resistance of avian pathogenic Escherichia coli isolated from broiler, layer, and breeder chickens

Background and Aim

Antimicrobials are extensively used in poultry production for growth promotion as well as for the treatment and control of diseases, including avian pathogenic Escherichia coli (APEC). Poor selection, overuse, and misuse of antimicrobial agents may promote the emergence and dissemination of antimicrobial resistance (AMR) in APEC. This study aimed to assess antimicrobial susceptibility patterns and detect antibiotic resistance genes (ARGs) in APEC isolated from clinical cases of colibacillosis in commercial broiler, layer, and breeder chickens.

Materials and Methods

A total of 487 APEC were isolated from 539 across 300 poultry farms in various regions of Nepal. Antimicrobial susceptibility patterns was determined using the Kirby-Bauer disk diffusion and broth microdilution methods. The index of AMR, such as multiple antibiotic resistance (MAR) index, resistance score (R-score), and multidrug resistance (MDR) profile, were determined. Polymerase chain reaction was employed to detect multiple ARGs and correlations between phenotypic and genotypic resistance were analyzed.

Results

The prevalence of APEC was 91% (487/539). All of these isolates were found resistant to at least one antimicrobial agent, and 41.7% of the isolates were resistant against 8-9 different antimicrobials. The antibiogram of APEC isolates overall showed the highest resistance against ampicillin (99.4%), whereas the highest intermediate resistance was observed in enrofloxacin (92%). The MAR index and R-score showed significant differences between broiler and layers, as well as between broiler breeder and layers. The number of isolates that were resistant to at least one agent in three or more antimicrobial categories tested was 446 (91.6%) and were classified as MDR-positive isolates. The ARGs were identified in 439 (90.1%) APEC isolates, including the most detected mobilized colistin resistance (mcr1) which was detected in the highest (52.6%) isolates. Overall, resistance gene of beta-lactam (blaTEM), mcr1, resistance gene of sulphonamide (sul1) and resistance gene of tetracycline (tetB) (in broiler), were detected in significantly higher than other tested genes (p < 0.001). When examining the pair-wise correlations, a significant phenotype-phenotype correlation (p < 0.001) was observed between levofloxacin and ciprofloxacin, chloramphenicol and tetracycline with doxycycline. Similarly, a significant phenotype-genotype correlation (p < 0.001) was observed between chloramphenicol and the tetB, and colistin with blaTEM and resistance gene of quinolone (qnrA).

Conclusion

In this study, the current state of APEC AMR in commercial chickens is revealed for the first time in Nepal. We deciphered the complex nature of AMR in APEC populations. This information of molecular surveillance is useful to combat AMR in APEC and to contribute to manage APEC associated diseases and develop policies and guidelines to enhance the commercial chicken production.

Antibiotic resistance pattern and pathological features of avian pathogenic Escherichia coli O78:K80 in chickens

Abstract Avian pathogenic Escherichia coli (APEC) induces colibacillosis, an acute and systemic disease, resulting in substantial economic losses in the poultry sector. This study aimed to investigate the antibiotic resistance pattern associated with frequent virulence gene distribution in APEC O78:K80 that may cause pathological alterations in chickens. The antibiogram profile showed high resistance to erythromycin, chloramphenicol, tetracycline, ampicillin, and co-trimoxazole, followed by intermediate resistance to ciprofloxacin, levofloxacin, enrofloxacin, norfloxacin, nitrofurantoin, and doxycycline hydrochloride, and sensitive to amikacin, streptomycin, gentamicin, and colistin. Virulence gene distribution identifies eight (irp-2, iutA, ompT, iss, iucD, astA, hlyF, iroN) genes through a conventional polymerase chain reaction. APEC O78:K80 caused significantly high liver enzyme concentrations, serum interleukin-6 and tumor necrosis factor-alpha levels in experimental birds. Also, infected birds have hypoproteinemia, hypoalbuminemia, and hyperglobulinemia. Necropsy examination revealed fibrinous perihepatitis and pericarditis, congested lungs, intestinal ecchymotic hemorrhages and necrotizing granulomatosis of the spleen. Histopathological examination depicted hepatocellular degeneration, myocardial necrosis, interstitial nephritis, intestinal hemorrhages and lymphopenia in the spleen. This study is the first evidence to assess the antibiotic resistance profile linked with virulence genes and clinicopathological potential of APEC O78:K80 in chickens in Pakistan, which could be a useful and rapid approach to prevent and control the disease by developing the control strategies.

Pharmacokinetics and antibacterial activity of tiamulin after single and multiple oral administrations in geese

Tiamulin is an antibiotic approved exclusively in veterinary medicine, active against G-positive bacteria as well as Mycoplasma spp. and Leptospirae spp. The study was aimed to establish its pharmacokinetics and to evaluate drug effects on resistance in cloacal flora in vivo in geese. Eight healthy geese underwent to a two-phase longitudinal study (60 mg/kg single oral administration vs 60 mg/kg/day for 4 days) with a two-week wash-out period. Blood samples and cloacal swabs were collected at pre-assigned times. Minimal inhibitory concentration (MIC) has been evaluated for each isolated bacterial species. The pharmacokinetic parameters that significantly differed between the groups were Cmax (p = 0.024), AUC0-t (p = 0.031), AUC0-inf (p = 0.038), t1/2kel (p = 0.021), Cl/F (p = 0.036), and Vd/F (p = 0.012). Tiamulin exhibited a slow to moderate terminal half-life (3.13 h single; 2.62 h multiple) and a rapid absorption (1 h single; 0.5 h multiple) in geese, with an accumulation ratio of 1.8 after multiple doses. An in-silico simulation of multiple dosing did not reflect the results of the in vivo multiple dosage study. In both treatments, the MIC values were very high demonstrating a resistance (> 64 μg/ml) against tiamulin that can be present prior the drug administration for some strains, or emerge shortly after the commencing of treatment for some others.

Spleen-based proteogenomics reveals that Escherichia coli infection induces activation of phagosome maturation pathway in chicken

Avian pathogenic Escherichia coli (APEC) leads to economic losses in poultry industry and is also a threat to human health. Various strategies were used for searching virulence factors, while little is known about the mechanism by which APEC survives in host or is eliminated by host. Thus, chicken colibacillosis model was constructed by intraperitoneally injecting E. coli O78 in this study, then the protein dynamic expression of spleen was characterized at different post-infection times by quantitative proteome. Comparative analysis showed that E. coli induced significant dysregulation at 72 h post infection in spleen tissue. Transcriptomic method was further used to assess the changes of dysregulated proteins at 72 h post infection at the mRNA level. Total 278 protein groups (5.7%) and 2,443 genes (24.4%) were dysregulated, respectively. The upregulated proteins and genes were consistently enriched in phagosome and lysosome pathways, indicating E. coli infection activates phagosome maturation pathway. The matured phagolysosome might kill the invasive E. coli. This study illuminated the genetic dysregulation in chicken spleen at the protein and mRNA levels after E. coli infecting and identified candidate genes for host response to APEC infection.

Pathotypes and Phenotypic Resistance to Antimicrobials of Escherichia coli Isolates from One-Day-Old Chickens

The aim of this work was to describe the pathotypes of Escherichia coli strains isolated from one-day-old chickens, as well as the occurrence of resistance and multidrug resistance (MDR) in these strains. A total of 429 mixed swabs from 4290 one-day-old chicks were examined between August 2021 and July 2023 (24 months) during routine point-of-destination inspections at 12 poultry farms in the Czech Republic. All samples were processed via cultivation methods using meat-peptone blood agar and Mc Conkey agar under aerobic conditions at 37 ± 1 °C for 18-24 h. The identification of the strains was performed using MALDI-TOF mass spectrometry. All confirmed strains of E. coli were screened via single or multiplex PCRs for the presence of genes encoding the virulence-associated factors iroN, cvaC, iss, felA, iutA, frz and tsh. Antimicrobial susceptibility tests were performed using the minimal inhibitory concentration (MIC) method, focusing on ampicillin, cefotaxime, tetracycline, doxycycline, enrofloxacin, florfenicol, amoxicillin with clavulanic acid and trimethoprim with sulfamethoxazole. A total of 321 E. coli strains (prevalence of 74.8%) were isolated, and 300 isolates were defined as avian pathogenic strains of E. coli (APEC) via multiplex PCR. Based on the defined virulence genes, the isolates were classified into 31 pathotypes. A total of 15.9% of the tested isolates were susceptible to all the tested antimicrobials. On the other hand, 20.5% of the isolates were identified as multidrug-resistant (8.7% of isolates were resistant to three antimicrobials, 7.3% to four antimicrobials, 3.6% to five antimicrobials and 0.9% to six antimicrobials). Monitoring pathogenic strains of E. coli in different animals and in the environment makes it possible to understand their spread in animal and human populations and, at the same time, reveal the sources of virulence and resistance genes.

Total infectome investigation of diphtheritic stomatitis in yellow-eyed penguins (Megadyptes antipodes) reveals a novel and abundant megrivirus

First identified in 2002, diphtheritic stomatitis (DS) is a devastating disease affecting yellow-eyed penguins (Megadyptes antipodes, or hoiho in te reo Māori). The disease is associated with oral lesions in chicks and has caused significant morbidity and mortality. DS is widespread among yellow-eyed penguin chicks on mainland New Zealand yet appears to be absent from the subantarctic population. Corynebacterium spp. have previously been suspected as causative agents yet, due to inconsistent cultures and inconclusive pathogenicity, their role in DS is unclear. Herein, we used a metatranscriptomic approach to identify potential causative agents of DS by revealing the presence and abundance of all viruses, bacteria, fungi and protozoa - together, the infectome. Oral and cloacal swab samples were collected from presymptomatic, symptomatic and recovered chicks along with a control group of healthy adults. Two novel viruses from the Picornaviridae were identified, one of which - yellow-eyed penguin megrivirus - was highly abundant in chicks irrespective of health status but not detected in healthy adults. Tissue from biopsied oral lesions also tested positive for the novel megrivirus upon PCR. We found no overall clustering among bacteria, protozoa and fungi communities at the genus level across samples, although Paraclostridium bifermentans was significantly more abundant in oral microbiota of symptomatic chicks compared to other groups. The detection of a novel and highly abundant megrivirus has sparked a new line of inquiry to investigate its potential association with DS.

Avian Pathogenic Escherichia coli (APEC) in Broiler Breeders: An Overview

Poultry meat is one of the major animal protein sources necessary to meet the global protein demand. Sustainability in broiler production is the key to achieving its continuous supply, and broiler breeders play a critical role in maintaining this sustainability by providing good quality chicks. Colibacillosis, the disease caused by avian pathogenic Escherichia coli (APEC), causes severe economic losses to the poultry industry globally. Moreover, APEC causes an additional burden among broiler breeders, such as a decrease in egg production and mortality among these birds. There is vertical transmission of APEC to the broiler chicks through eggs, resulting in increased first-week mortality and subsequent horizontal transmission at the hatchery. In this regard, the vertical transmission of antibiotic resistance genes is another concern that needs attention. Controlling several diseases in broiler breeders would possibly reduce the first-week mortality in chicks, thereby maintaining the production level. For that, constant monitoring of the bacterial populations is critical. Moreover, amidst the increased antibiotic resistance pattern, more focus on alternative treatment strategies like vaccines, probiotics, and bacteriophages is necessary. Future research focusing on strategies to mitigate APEC in broiler breeders would be one of the finest solutions for sustainable broiler production.

Extracellular vesicles produced by avian pathogenic Escherichia coli (APEC) activate macrophage proinflammatory response and neutrophil extracellular trap (NET) formation through TLR4 signaling

BACKGROUND

Avian pathogenic Escherichia coli (APEC) is the major pathogen causing important avian diseases in poultry. As an important subtype of extraintestinal pathogenic E. coli, APEC has zoonotic potential and is considered a foodborne pathogen. APEC extracellular vesicles (EVs) may play vital roles in the interaction of the pathogen with its host cells. However, the precise roles played by APEC EVs are still not completely clear, especially in immune cells.

RESULTS

In this study, we investigated the relationships between APEC EVs and immune cells. The production and characteristics of the EVs of APEC isolate CT265 were identified. Toll like receptor 4 (TLR4) triggered the cellular immune responses when it interacted with APEC EVs. APEC EVs induced a significant release of proinflammatory cytokines in THP-1 macrophages. APEC EVs induced the macrophage inflammatory response via the TLR4/MYD88/NF-κB signaling pathway, which participated in the activation of the APEC-EV-induced NLRP3 inflammasome. However, the loss of lipopolysaccharide (LPS) from APEC EVs reduced the activation of the NLRP3 inflammasome mediated by TLR4/MYD88/NF-κB signaling. Because APEC EVs activated the macrophage inflammatory response and cytokines release, we speculated that the interaction between APEC EVs and macrophages activated and promoted neutrophil migration during APEC extraintestinal infection. This study is the first to report that APEC EVs induce the formation of neutrophil extracellular traps (NETs) and chicken heterophil extracellular traps. Treatment with APEC EVs induced SAPK/JNK activation in neutrophils. The inhibition of TLR4 signaling suppressed APEC-EV-induced NET formation. However, although APEC EVs activated the immune response of macrophages and initiated NET formation, they also damaged macrophages, causing their apoptosis. The loss of LPS from APEC EVs did not prevent this process.

CONCLUSION

APEC-derived EVs induced inflammatory responses in macrophages and NETs in neutrophils, and that TLR4 was involved in the APEC-EV-activated inflammatory response. These findings provided a basis for the further study of APEC pathogenesis.

Antimicrobial Efficacy of Cinnamon Essential Oil against Avian Pathogenic Escherichia coli from Poultry

Colibacillosis, caused by E. coli, is responsible for economic losses in the poultry industry due to mortality, decreased production, and the cost of antibiotic treatments. Prevention of colibacillosis is based on improved biosecurity measures and the use of the vaccine performed with O78 E. coli strains, which is responsible for most cases of colibacillosis. Recently, there has been increased interest in other infection control methods, such as the use of natural compounds. The aim of this study was to evaluate the antimicrobial efficacy of cinnamon essential oil (CEO) against E. coli strains isolated from poultry. The MIC50 and MIC90 of CEO were determined by testing 117 strains belonging to serogroups O78, O2, O128, O139, isolated from laying hens (91 strains), broilers (10 strains), and turkeys (16 strains). The bacterial strains were tested at cell densities of 108 and 106 CFU/mL. At the cell density of 108 CFU/mL, MIC50 and MIC90 were 0.4 and 0.5 µL/mL for most of the tested strains, while they corresponded to 0.5 µL/mL for all strains isolated from broilers and for strains belonging to serogroup O139. At the cell density of 106 CFU/mL, MIC50 and MIC90 were 0.3 and 0.4 µL/mL, regardless of bird species of origin and for strains belonging to serogroups O78 and O2. In addition, a concentration of 0.04 µL/mL of CEO corresponded both to MIC50 and MIC90 for strains belonging to serogroups O139 and O128. Based on these results, cinnamon essential oil showed an effective antibacterial activity against E. coli strains from poultry and could find field application for the prevention of colibacillosis.

Efficacy of zinc oxide and copper oxide nanoparticles on virulence genes of avian pathogenic E. coli (APEC) in broilers

BACKGROUND

Colibacillosis is one of the broilers' most dominant bacterial diseases, either as a primary or a secondary infection. As E. coli antimicrobial drug resistance is rising; there is a need to develop new approaches to its control. In light of this, a comparative study of the in-vitro antibacterial activity of Arabic gum stabilized zinc and copper nanoparticles (AG-ZnNPs and AG-CuNPs) against PCR-identified field avian pathogenic E. coli (APEC) strains and virulence genes (ibeA, hlyA, iss, pap C and ompA) was applied to study the therapeutic effect of zinc and copper nanoparticles to be used as an antibiotic alternative (Nanobiotic). Furthermore, the in-vivo effects of CuNPs were evaluated. Additionally, the CuNPs liver and muscle residues with or without infection were examined. The eighty broilers were divided into four groups; G1: negative control, G2: infected control with E. coli O17, G3: non-infected treated (AG-CuNPs 50 mg/kg body weight), and G4: infected treated (AG-CuNPs 50 mg/kg body weight). AG-CuNPs treatment was given to broilers for five days in drinking water.

RESULTS

E. coli was isolated from diseased broilers at an average incidence rate of 20% from intestinal and liver samples. All identified serotypes (O17, O78, O91, O121, and O159) were resistant to AG-ZnNPs and sensitive to AG-CuNPs. AG-CuNPs minimal inhibitory and bactericidal concentrations (MIC and MBC) for O17 were 7.5 and 60 mg/ml, respectively. Conventional uniplex PCR results showed that strain O17 contained virulence genes (ibeA, hlyA, iss, and papC), where AG-CuNPs significantly reduced the expression of all target genes when examined by Real-time quantitative PCR. Additionally, the bactericidal activity of AG-CuNPs on O17 was 100% at 20 minutes and 40 mg/ml and confirmed by transmission electron microscopy. Furthermore, no mortality was recorded in treated groups compared to G2. Subsequently, no E. coli was re-isolated from the liver in the G4 after treatment. The total protein, albumin, globulin, and lysozyme activity were significantly increased in G4 compared to G2, while the activities of liver enzymes (alanine aminotransferase (ALT), Gamma-glutamyl transferase (GGT), and alkaline phosphatase (ALP)) were markedly decreased in G4 compared to G2. Additionally, uric acid, creatinine, and C-reactive protein levels were decreased in G4 compared to G2. However, the liver enzymes, kidney functions, C-reactive protein levels, and Cu residues were non-significantly changed in G4 compared to G1.

CONCLUSION

Green synthesized AG-CuNPs are recommended as an effective antimicrobial alternative against APEC strains.

Characterization of two novel lytic bacteriophages having lysis potential against MDR avian pathogenic Escherichia coli strains of zoonotic potential

Avian pathogenic E. coli (APEC) is associated with local and systemic infections in poultry, ducks, turkeys, and many other avian species, leading to heavy economical losses. These APEC strains are presumed to possess zoonotic potential due to common virulence markers that can cause urinary tract infections in humans. The prophylactic use of antibiotics in the poultry sector has led to the rapid emergence of Multiple Drug Resistant (MDR) APEC strains that act as reservoirs and put human populations at risk. This calls for consideration of alternative strategies to decrease the bacterial load. Here, we report isolation, preliminary characterization, and genome analysis of two novel lytic phage species (Escherichia phage SKA49 and Escherichia phage SKA64) against MDR strain of APEC, QZJM25. Both phages were able to keep QZJM25 growth significantly less than the untreated bacterial control for approximately 18 h. The host range was tested against Escherichia coli strains of poultry and human UTI infections. SKA49 had a broader host range in contrast to SKA64. Both phages were stable at 37 °C only. Their genome analysis indicated their safety as no recombination, integration and host virulence genes were identified. Both these phages can be good candidates for control of APEC strains based on their lysis potential.

Aerosol vaccination of chicken pullets with irradiated avian pathogenic Escherichia coli induces a local immunostimulatory effect

The present study investigated the expression of cytokines and cellular changes in chickens following vaccination with irradiated avian pathogenic Escherichia coli (APEC) and/or challenge. Four groups of 11-week-old pullets, each consisting of 16 birds were kept separately in isolators before they were sham inoculated (N), challenged only (C), vaccinated (V) or vaccinated and challenged (V+C). Vaccination was performed using irradiated APEC applied via aerosol. For challenge, the homologous strain was administered intratracheally. Birds were sacrificed on 3, 7, 14 and 21 days post challenge (dpc) to examine lesions, organ to body weight ratios and bacterial colonization. Lung and spleen were sampled for investigating gene expression of cytokines mediating inflammation by RT-qPCR and changes in the phenotype of subsets of mononuclear cells by flow cytometry. After re-stimulation of immune cells by co-cultivation with the pathogen, APEC-specific IFN-γ producing cells were determined. Challenged only birds showed more severe pathological and histopathological lesions, a higher probability of bacterial re-isolation and higher organ to body weight ratios compared to vaccinated and challenged birds. In the lung, an upregulation of IL-1β and IL-6 following vaccination and/or challenge at 3 dpc was observed, whereas in the spleen IL-1β was elevated. Changes were observed in macrophages and TCR-γδ⁺ cells within 7 dpc in spleen and lung of challenged birds. Furthermore, an increase of CD4⁺ cells in spleen and a rise of Bu-1⁺ cells in lung were present in vaccinated and challenged birds at 3 dpc. APEC re-stimulated lung and spleen mononuclear cells from only challenged pullets showed a significant increase of IFN-γ⁺CD8α⁺ and IFN-γ⁺TCR-γδ⁺ cells. Vaccinated and challenged chickens responded with a significant increase of IFN-γ⁺CD8α⁺ T cells in the lung and IFN-γ⁺TCR-γδ⁺ cells in the spleen. Re-stimulation of lung mononuclear cells from vaccinated birds resulted in a significant increase of both IFN-γ⁺CD8α⁺ and IFN-γ⁺TCR-γδ⁺ cells. In conclusion, vaccination with irradiated APEC caused enhanced pro-inflammatory response as well as the production of APEC-specific IFN-γ-producing γδ and CD8α T cells, which underlines the immunostimulatory effect of the vaccine in the lung. Hence, our study provides insights into the underlying immune mechanisms that account for the defense against APEC.

The transcriptional regulator EtrA mediates ompW contributing to the pathogenicity of avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) causes avian colibacillosis and leads to high mortality in poultry and huge economic losses. Therefore, it is important to investigate the pathogenic mechanisms of APEC. Outer membrane protein OmpW is involved in the environmental adaptation and pathogenesis of Gram-negative bacteria. OmpW is regulated by many proteins, including FNR, ArcA, and NarL. In previous studies, regulator EtrA is involved in the pathogenicity of APEC and affects the transcript levels of ompW. However, the function of OmpW in APEC and its regulation remain unclear. In this study, we constructed mutant strains with altered etrA and/or ompW genes to evaluate the roles of EtrA and OmpW in the biological characteristics and pathogenicity of APEC. Compared with wild-type strain AE40, mutant strains ∆etrA, ∆ompW, and ∆etrA∆ompW showed significantly lower motility, lower survival under external environmental stress, and lower resistance to serum. Biofilm formation by ∆etrA and ∆etrA∆ompW was significantly enhanced relative to that of AE40. The transcript levels of TNF-α, IL1β, and IL6 were also significantly enhanced in DF-1 cells infected with these mutant strains. Animal infection assays showed that deletion of etrA and ompW genes attenuated the virulence of APEC in chick models, and damage to the trachea, heart, and liver caused by these mutant strains was attenuated relative to that caused by the wild-type strain. RT-qPCR and β-galactosidase assay showed that EtrA positively regulates the expression of the ompW gene. These findings demonstrate that regulator EtrA positively regulates the expression of OmpW, and that they both contribute to APEC motility, biofilm formation, serum resistance, and pathogenicity.