Virulence of Escherichia coli Isolates Obtained from Layer Chickens with Colibacillosis Associated with Pericarditis, Perihepatitis, and Salpingitis in Experimentally Infected Chicks and Embryonated Eggs

Phenotypic virulence characterization of avian pathogenic Escherichia coli (APEC) isolates from broiler breeders with colibacillosis in Mississippi

AIMS

In this study, we evaluated the phenotypic virulence characteristics of avian pathogenic Escherichia coli (APEC) isolates from broiler breeders with colibacillosis in Mississippi. Also, the relationship between phenotypic and genotypic virulence patterns was determined.

METHODS AND RESULTS

Twenty-eight APEC isolated from lesions of broiler breeders diagnosed with colibacillosis were used for embryo lethality assay and chick challenge study. The percentage of embryo mortality following embryo lethality assay and pathogenicity score following the chick challenge study were used to categorize the isolates based on virulence. Pearson correlation analysis was performed to determine the relationship between embryo mortality, chick pathogenicity, and the presence of virulence-associated genes in the isolates. Overall, 39.3% of the isolates were highly virulent and 3.5% were avirulent, following both assays. There existed a positive correlation between embryo mortality and chick pathogenicity (r = 0.73, P < .01), as well as percentage embryo mortality and pathogenicity score with the presence of some virulence genes.

CONCLUSIONS

Even though all the APEC were isolated from lesions of diseased breeders, the virulence potential varied from being avirulent to highly virulent. Further, we identified a positive relationship between phenotypic virulence and the frequency of virulence-associated genes.

Control of Escherichia coli in Poultry Using the In Ovo Injection Technique

Pathogens, such as Escherichia coli (E. coli), have been identified as significant causes of poultry mortality. Poultry can serve as potential sources of E. coli transmission, even when asymptomatic, posing a substantial threat to food safety and human health. The in ovo administration of antimicrobials is crucial for preventing and/or effectively combating acute and chronic infections caused by poultry pathogens. To achieve this goal, it is critical that antimicrobials are properly injected into embryonic fluids, such as the amnion, to reach target tissues and trigger robust antimicrobial responses. Several protocols based on antimicrobials were evaluated to meet these requirements. This review analyzed the impacts of antimicrobial substances injected in ovo on the control of E. coli in poultry. The reduction in infection rates, resulting from the implementation of in ovo antimicrobials, combined with efforts aimed at hygienic-sanitary action plans in poultry sheds, reinforces confidence that E. coli can be contained before causing large scale damage. For example, antimicrobial peptides and probiotics have shown potential to provide protection to poultry against infections caused by E. coli. Issues related to the toxicity and bacterial resistance of many synthetic chemical compounds represent challenges that need to be overcome before the commercial application of in ovo injection protocols focused on microbiological control.

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.

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.

Lotus leaf extract can attenuate salpingitis in laying hens by inhibiting apoptosis

This study aimed to determine whether the lotus leaf extract (LLE) had the effect of treating salpingitis in laying hens. First, the salpingitis model was established by the method of bacterial infection. Differential genes between salpingitis and healthy laying hens were identified by transcriptome sequencing, and GO and KEGG enrichment analyses were performed. Groups of treatment of antibiotics and LLE were established to verify the feasibility of the lotus leaf extract in treating salpingitis. Furthermore, the active component and pharmacological effects of LLE were identified using the UPLC-Q-TOF-MS and network pharmacology technique. At last, the mechanism of LLE treating salpingitis was further evaluated by DF-1 cells infected with bacteria. The results showed that LLE significantly reduced the levels of TLR4 and IFN-γ (P < 0.05), accelerated the levels of IgA and IgG (P < 0.05), regulated the levels of SOD and MDA (P < 0.05) in laying hens with salpingitis. A total of 1,874 differential genes were obtained according to the transcriptome sequencing. It was revealed a significant role in cell cycle and apoptosis by enrichment analysis. In addition, among the 28 components identified by UPLC-Q-TOF-MS, 20 components acted on 58 genes, including CDK1, BIRC5, and CA2 for treating salpingitis. After bacterial infection, cells were damaged and unable to complete the normal progression of the cell cycle, leading to cell cycle arrest and further apoptosis formation. However, with the intervention of LLE, bacterial infection was resisted. The cells proliferation was extensively restored, and the expression of NO was increased. The addition of LLE significantly decreased cell apoptosis. The G1 phase increased, the S phase and the G2 phase decreased in the model group; after the intervention of LLE, the G1 phase gradually returned to the average level, and G2 and S phases increased. The mRNA expression levels of BIRC5, CDK1, and CA2 were consistent with the predicted results in network pharmacology. At the same time, the mRNA expression levels of Caspase-3 and Caspase-7 were reduced after added with LLE. The mRNA expression levels of TNF-α, TRADD, FADD, Caspase-8, Caspase-10, and Caspase-9 (P < 0.05), which would inhibit death receptor activation and decrease the apoptotic cascade, were upregulated after bacterial infection. However, the results in LLE groups were downregulated (P < 0.05). Meanwhile, the mRNA expression levels of BCL-2 in LLE groups were increased significantly compared with it in model group (P < 0.05). Notably, LLE administration inhibited apoptosis and regulated the cell cycle distribution in the salpingitis induced by bacterial infection. These results indicated that the LLE attenuated bacterial-induced salpingitis by modulating apoptosis and immune function in laying hens.

Chicken embryo lethality assay for determining the lethal dose, tissue distribution and pathogenicity of clinical Enterococcus cecorum isolates from poultry

Enterococcus cecorum is a well-known component of the normal poultry intestinal microbiota and an important bacterial pathogen. Infections caused by E. cecorum have negative effects on the poultry production worldwide. In this study we used the SPF-chicken embryo lethality assay (ELA) to assess the pathogenic potential of E. cecorum. A total of 23 isolates were used: 19 clinical isolates from field outbreaks in different poultry groups (CB – broiler chickens, BB – broiler breeders, CL – layers, T– turkeys, W – waterfowl) and 4 commensal isolates. The cumulative mortality caused by all clinical isolates was higher (53.4%) than that of the commensals (38.9%). The highest mortality was induced by CB isolates (68.9%), followed by CL (60.4%), all chicken isolates (59.2%; CB, BB, CL), BB (45.8%), T (41.7%), non-chicken isolates (40.7%; T, W), and W isolates (39.8%). Most of the embryos that died, did die on the 1st day post-infection (dpi), except those infected with CB, CL (on 2 dpi). The median lethal dose (LD₅₀) of E. cecorum ranged from 6.07 × 10² cfu/ml (CB isolates) and 1.42 × 10⁴ cfu/ml (all clinical isolates) to 4.8 × 10⁵ cfu/ml (commensal isolates). This study provides the first evidence of a wide tissue distribution and multiplication of E. cecorum in embryos. Dead embryos showed scattered petechiae, hemorrhages, aggregates of bacteria in blood vessels, multiple organ necrosis, and encephalomalacia. Our data indicate that surviving embryos were able to elicit innate immune response to infection. On the other hand, reisolation of viable bacteria from surviving embryos may suggest that E. cecorum could evade or resist immune mechanisms in order to persist in organs. Furthermore, body mass of surviving embryos was affected by the strain type, not the dose (bacterial concentration) used, and was lower for the infection with clinical strains. The results indicated the highest pathogenicity of clinical E. cecorum isolates from CB and CL flocks.

Relationship between Phylogenetic Groups of Escherichia coli and Pathogenicity Among Isolates from Chickens with Colibacillosis and Healthy Chickens

Avian pathogenic Escherichia coli (APEC) is closely related to extraintestinal pathogenic E. coli, which are frequently assigned to specific phylogenetic groups (phylogroups). Therefore, we investigated the association between phylogroups of E. coli isolates and those recovered from commercial broiler and layer chickens with colibacillosis. We used 104 E. coli isolates from chickens with colibacillosis (hereafter referred to as “colibacillosis-related isolates”), 56 E. coli isolates obtained from fecal samples of clinically healthy broiler chickens, and 58 isolates obtained from environmental samples of layer chicken housing facilities where clinically healthy layer chickens were reared (hereafter referred to as “healthy chicken-related isolates”). The prevalence of phylogroup F among colibacillosis-related isolates was significantly (P < 0.05) higher than that among healthy chicken-related isolates, while phylogroups A and B1 were more frequently distributed in healthy chicken-related isolates. Fifty-seven (87%) of 65 colibacillosis-related isolates belonging to phylogroup F were defined as APEC based on the presence of virulence-associated genes according to a previously established criterion. In contrast, none of the healthy chicken-related isolates were defined as APEC. As evidenced by the chicken embryo lethality assay, 87 of the 92 healthy chicken-related isolates tested had embryo lethality rates of <30% and were considered avirulent, whereas 59 of the 104 colibacillosis-related isolates were considered virulent. Nonetheless, among isolates exhibiting embryo lethality rates of <30%, the mean lethality rate of embryos inoculated with colibacillosis-related isolates was significantly higher than that of embryos inoculated with healthy chicken-related isolates. These observations suggest that phylogroup F predicts colibacillosis among E. coli strains with virulence-associated genes.

Virulence-Associated Gene Profiles of Escherichia coli Isolated from Chickens with Colibacillosis in Japan and Their Correlation with Pathogenicity in Chicken Embryos

Colibacillosis, an infectious disease of chickens, is caused by avian pathogenic Escherichia coli (APEC); however, in addition to APEC, other pathogens are also frequently isolated from chickens affected with colibacillosis. Therefore, experimental infections in chickens are necessary to evaluate the pathogenicity of APEC isolates. Recent studies have shown that embryo lethality assays can be used as an alternative method to evaluate the pathogenicity of E. coli. In this study, to determine the important virulence genes associated with the pathogenicity of E. coli, 67 strains of E. coli that possessed different combinations of eight representative virulence genes (cva/cvi, vat, tsh, iucD, papC, irp2, iss, and astA) were isolated from broilers with colibacillosis in Japan, and the chicken embryo lethal assay was conducted. The genes vat, papC, and irp2 showed strong correlation with the level of virulence in E. coli. Our study provides useful information about the important virulence-associated genes in relation to the pathogenicity of E. coli in Japanese chickens.

Effects of aroA deleted E. coli vaccine on intestinal microbiota and mucosal immunity

E. coli infection of broilers can result in systemic diseases and productivity losses. Use of antimicrobials against this condition is common but other approaches, such as vaccination, are gaining ground. Anecdotal field reports indicate that intestinal health is improved unspecifically following E. coli live vaccination. We hypothesized that the intestine may be an important site for the functionality of the vaccine. Vaccine effects on the intestine were assessed. Spray vaccination induced marked alterations of the caecum microbiota of broilers within 3 days, and this effect gradually waned. However, T cell activation occurred in the spleen, but not in caecal tonsils, and anti-E. coli IgA was concentrated in the respiratory mucosae. Accordingly, IL-6 mRNA was produced in the lungs following immunization. Overall, these data are an initial indication that any vaccine-induced effects on the intestine are greatly associated with the microbiota. However, immunity conferred by vaccination is not primarily induced in gut-associated lymphoid tissues.

Pathogenicity of the avian Escherichia coli isolates from pericarditis and femoral head necrosis lesions of the colibacillosis in experimentally infected chicks

The aim of the present study was to evaluate the relationship between different combinations of seven (ompT, hlyF, iss, iutA, iroN, tsh and cvaC) Colicin V (ColV) plasmid associated virulence genes (VGs) and pathogenicity of avian E. coli isolates. After detection of the different patterns of VGs among 290 E. coli isolates from pericarditis and femoral head necrosis lesions of colibacillosis and the 70 isolates from feces of apparently healthy birds (AFEC), the day-old chick lethality test was conducted. Distribution of genetic patterns was different between the APECs and AFECs isolates, so that 67.3% of the APECs typed were represented by two specific genetic patterns (ompT+/hlyF+/iss+/iutA+/iroN+/tsh+/cvaC+; ompT+/hlyF+/iss+/iutA+/iroN+/tsh+/cvaC-). Furthermore, both the APECs and AFECs isolates with different genetic patterns were lethal for day-old chicks. The ColV plasmid or some of its VGs can provide helpful characteristics to describe APECs. Furthermore, extraintestinal environments may supply requirements for the pathogenicity of the avian E. coli isolates harboring different genetic background. However, further studies are needed to confirm the definite link between avian E. coli isolates pathogenicity and their genotype.