Virulence Gene Distribution of Salmonella Pullorum Isolates Recovered from Chickens in China (1953-2015)

Genome-wide association analysis reveals genetic loci and candidate genes for white diarrhea in Jingyuan chickens

In order to investigate the basic genetic structure of dysentery in Jingyuan chickens and to explore the genetic markers associated with dysentery resistance in chickens, the present study was based on the genome-wide association analysis (GWAS) technique to investigate the candidate SNPs and genes associated with dysentery resistance in Jingyuan chickens, and a total of 12 SNPs were associated with dysentery resistance in Jingyuan chickens. In addition, some important candidate genes inciuding frizzled class receptor 4 (FZD4), DDB1 and CUL4 associated factor 13(DCAF13), regulating synaptic membrane exocytosis 2 (RIMS2), transmembrane protein 8C (TMEM8C), and RIC1 homolog (RIC1) were identified by selection signal analysis, gene annotation, and enrichment analysis. These results can be used as potential molecular selection markers for chicken dysentery resistance in Jingyuan chickens in order to improve the breeding of disease resistance in Jingyuan chickens.

Efficient differentiation between Salmonella Pullorum and Salmonella Gallinarum by a fimH-based PCR-HRM

Salmonella Pullorum (S. Pullorum) and Salmonella Gallinarum (S. Gallinarum) are the biovars of Salmonella enterica serovar Gallinarum that are responsible for pullorum disease and fowl typhoid, respectively, in poultry. Traditional serological methods fail to quickly differentiate between these biovars due to their identical O antigenic factors (O9 and O12). Although single nucleotide polymorphism (SNP)-based methods have been used to distinguish between the biovars, they often lack the required accuracy and effectiveness. In this study, we developed a PCR high resolution melt (PCR-HRM) assay, which targeted a SNP at position 665 of the fimH gene, for rapid differentiation between S. Pullorum and S. Gallinarum. Our method showed 100% specificity and was able to detect as little as 0.033 pg of S. Pullorum DNA and 0.027 pg of S. Gallinarum DNA. The PCR-HRM results for 547 clinical isolates were in complete agreement with traditional serological methods. This PCR-HRM assay significantly reduced identification time and provided high throughput, efficient testing. This makes it a practical and reliable tool for accurate differentiation between S. Pullorum and S. Gallinarum in clinical settings.

Genome-Based Analysis of Genetic Diversity, Antimicrobial Susceptibility, and Virulence Gene Distribution in Salmonella Pullorum Isolates from Poultry in China

Pullorum disease, caused by Salmonella enterica serovar Pullorum (S. Pullorum) infection, is a major pathogenic threat to the poultry industry. In this study, 40 S. Pullorum isolates from seven provinces of China were comprehensively analyzed in terms of antigenic type and antimicrobial susceptibility, and their drug-resistance genes and virulence genes were identified with whole-genome sequencing (WGS). We show that all these isolates were standard antigenic types, with ST92 the predominant genotype (92.5%). Disk diffusion assays revealed high resistance rates to streptomycin (92.5%), ciprofloxacin (82.5%), and ampicillin (80%), and the resistance rates to streptomycin, gentamicin, ampicillin, and cefotaxime were higher in isolates from sick chickens than in those from healthy chickens. In addition, gyrA mutations and eight acquired resistance genes were identified, with aac(6')-Iaa the most prevalent, followed by blaTEM1β, sul2, and the GyrA S83F mutation. The resistance phenotypes to streptomycin, ampicillin, and ciprofloxacin correlated strongly with the presence of the aac(6')-Iaa resistance gene, blaTEM1β resistance gene, and gyrA mutations, respectively. Analysis of the virulence genes showed that the isolates expressed numerous factors associated with secretion systems, including SPI-1 and SPI-2. Overall, this study extends our understanding of the epidemiology and antibiotic resistance of S. Pullorum in China.

Evolution and genomic profile of Salmonella enterica serovar Gallinarum biovar Pullorum isolates from Brazil

Salmonella enterica subspecies enterica serovar Gallinarum biovar Pullorum (S. Pullorum) is a pathogenic bacterium that causes Pullorum disease (PD). PD is an acute systemic disease that affects young chickens, causing white diarrhea and high mortality. Although many sanitary programs have been carried out to eradicate S. Pullorum, PD outbreaks have been reported in different types of birds (layers, broilers, breeders) worldwide. This study aimed to evaluate the evolution and genetic characteristics of S. Pullorum isolated from PD in Brazil. Phylogenetic analysis of S. Pullorum genomes sequenced in this study and available genomic databases demonstrated that all isolates from Brazil are from sequence type 92 (ST92) and cluster into two lineages (III and IV). ColpVC, IncFIC(FII), and IncFII(S) were plasmid replicons frequently found in the Brazilian lineages. Two resistance genes (aac(6')-Iaa, conferring resistance to aminoglycoside, disinfecting agents, and antiseptics (mdf(A)) and tetracycline (mdf(A)) were detected frequently. Altogether, these results are important to understand the circulation of S. Pullorum and, consequently, to develop strategies to reduce losses due to PD.

Unravelling the role of anaerobic metabolism (pta-ackA) and virulence (misL and ssa) genes in Salmonella Heidelberg shedding using chicken infection model

The mechanism of colonisation of the chicken intestine by Salmonella remains poorly understood, while the severity of infections vary enormously depending on the serovar and the age of the bird. Several metabolism and virulence genes have been identified in Salmonella Heidelberg; however, information on their roles in infection, particularly in the chicken infection model, remains scarce. In the present publication, we investigated three Salmonella Heidelberg mutants containing deletions in misL, ssa, and pta-ackA genes by using signature-tagged mutagenesis. We found that mutations in these genes of S. Heidelberg result in an increase in fitness in the chicken model. The exception was perhaps the pta-ackA mutant where colonisation was slightly reduced (2, 7, 14, and 21 days post-infection) although some birds were still excreting at the end of the experiment. Our results suggest that for intestinal colonisation of the chicken caecum, substrate-level phosphorylation is likely to be more important than the MisL outer membrane protein or even the secretion system apparatus. These findings validate previous work that demonstrated the contribution of ackA and pta mutants to virulence in chickens, suggesting that the anaerobic metabolism genes such as pta-ackA could be a promising mitigation strategy to reduce S. Heidelberg virulence.

Unveiling the Potential Ways to Apply Citrus Oil to Control Causative Agents of Pullorum Disease and Fowl Typhoid in Floor Materials

This study investigates the potential role of Cold-pressed Valencia Terpeneless citrus oil (CO), as a natural antimicrobial, in controlling causative agents of pullorum disease and fowl typhoid in floor materials for poultry farming, specifically wooden chips. The study addresses the issues that have arisen as a result of the reduction in antibiotic use in poultry farming, which has resulted in the re-emergence of bacterial diseases including salmonellosis. CO efficiently inhibits the growth of pathogens including various serovars of Salmonella enterica (SE), including SE serovar Gallinarum (S. Gallinarum) and SE serovar Pullorum (S. Pullorum), in a dose-dependent manner. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of CO showed potential for controlling diverse S. Gallinarum and S. Pullorum isolates. Growth inhibition assays demonstrated that 0.4% (v/w) CO eliminated S. Pullorum and S. Gallinarum from 24 h onwards, also impacting poultry gut microbiota and probiotic strains. Floor material simulation, specifically wooden chips treated with 0.4% CO, confirmed CO's effectiveness in preventing S. Gallinarum and S. Pullorum growth on poultry house floors. This study also investigated the effect of CO on the expression of virulence genes in S. Gallinarum and S. Pullorum. Specifically, the study revealed that the application of CO resulted in a downregulation trend in virulence genes, including spiA, invA, spaN, sitC, and sifA, in both S. Pullorum and S. Gallinarum, implying that CO may alter the pathogenicity of these bacterial pathogens. Overall, this study reveals that CO has the potential to be used as a natural antimicrobial in the prevention and management of Salmonella-related infections in chicken production, offering a viable alternative to control these re-emerging diseases.

Genomic Diversity, Antimicrobial Resistance, Plasmidome, and Virulence Profiles of Salmonella Isolated from Small Specialty Crop Farms Revealed by Whole-Genome Sequencing

Salmonella is the leading cause of death associated with foodborne illnesses in the USA. Difficulty in treating human salmonellosis is attributed to the development of antimicrobial resistance and the pathogenicity of Salmonella strains. Therefore, it is important to study the genetic landscape of Salmonella, such as the diversity, plasmids, and presence antimicrobial resistance genes (AMRs) and virulence genes. To this end, we isolated Salmonella from environmental samples from small specialty crop farms (SSCFs) in Northeast Ohio from 2016 to 2021; 80 Salmonella isolates from 29 Salmonella-positive samples were subjected to whole-genome sequencing (WGS). In silico serotyping revealed the presence of 15 serotypes. AMR genes were detected in 15% of the samples, with 75% exhibiting phenotypic and genotypic multidrug resistance (MDR). Plasmid analysis demonstrated the presence of nine different types of plasmids, and 75% of AMR genes were located on plasmids. Interestingly, five Salmonella Newport isolates and one Salmonella Dublin isolate carried the ACSSuT gene cassette on a plasmid, which confers resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, and tetracycline. Overall, our results show that SSCFs are a potential reservoir of Salmonella with MDR genes. Thus, regular monitoring is needed to prevent the transmission of MDR Salmonella from SSCFs to humans.

Prevalence and Characterization of Salmonella Isolated from Chickens in Anhui, China

Salmonella is one of the most important zoonotic pathogens that can cause both acute and chronic illnesses in poultry flocks, and can also be transmitted to humans from infected poultry. The purpose of this study was to investigate the prevalence, antimicrobial resistance, and molecular characteristics of Salmonella isolated from diseased and clinically healthy chickens in Anhui, China. In total, 108 Salmonella isolates (5.66%) were successfully recovered from chicken samples (n = 1908), including pathological tissue (57/408, 13.97%) and cloacal swabs (51/1500, 3.40%), and S. Enteritidis (43.52%), S. Typhimurium (23.15%), and S. Pullorum (10.19%) were the three most prevalent isolates. Salmonella isolates showed high rates of resistance to penicillin (61.11%), tetracyclines (47.22% to tetracycline and 45.37% to doxycycline), and sulfonamides (48.89%), and all isolates were susceptible to imipenem and polymyxin B. In total, 43.52% isolates were multidrug-resistant and had complex antimicrobial resistance patterns. The majority of isolates harbored cat1 (77.78%), blaTEM (61.11%), and blaCMY-2 (63.89%) genes, and the antimicrobial resistance genes in the isolates were significantly positively correlated with their corresponding resistance phenotype. Salmonella isolates carry high rates of virulence genes, with some of these reaching 100% (invA, mgtC, and stn). Fifty-seven isolates (52.78%) were biofilm-producing. The 108 isolates were classified into 12 sequence types (STs), whereby ST11 (43.51%) was the most prevalent, followed by ST19 (20.37%) and ST92 (13.89%). In conclusion, Salmonella infection in chicken flocks is still serious in Anhui Province, and not only causes disease in chickens but might also pose a threat to public health security.

Graphene oxide-assisted optimized narrow-thermal-cycling amplification for accurate detection of Salmonella spp

Salmonella is a rod-shaped, Gram-negative zoonotic pathogen that poses a serious global socioeconomic and public health threat. Rapid and accurate detection of Salmonella spp. is critical for effective control of its infection. In this study, an accurate, sensitive and specific graphene oxide-assisted accelerated strand exchange amplification (GO-ASEA) method for rapid detection of Salmonella spp. was developed and validated. The detection limit of the GO-ASEA method was 8.6 × 10¹ fg μL^-1 of Salmonella genomic DNA or 1 × 10¹ CFU g^-1 of Salmonella in spiked chicken faeces free of pre-enrichment. And the GO-ASEA method could specifically detect Salmonella spp. without cross-reactivity with other enteric pathogens. In addition, the novel method achieved Salmonella detection within 30 min and was validated using 209 clinical samples, showing its good clinical applicability. Therefore, the GO-ASEA method is a new optional tool for the rapid detection of pathogenic microorganisms, which is ideal for food safety monitoring and high-throughput detection.

Molecular characterization of virulence genes in poultry-originated Salmonella Enteritidis and Salmonella Typhimurium

Salmonella Enteritidis and Salmonella Typhimurium are the most common serovars observed in human salmonellosis while contaminated poultry products are the major source of Salmonella transmission to humans. Therefore, high pathogenicity of poultry-originated S. Enteritidis and S. Typhimurium strains poses a serious risk to human health. This study analyzed the virulence genes of broiler chicken-originated S. Enteritidis and S. Typhimurium strains. SipA, sipD, sopB, sopD, sopE, sopE2, sitC, sifA, ssaR, spvC and pefA genes were investigated in a total of 137 strains consisting of 105 S. Enteritidis and 32 S. Typhimurium. Nine strains (6.6%) had all genes. No negative strain was detected for all genes. SopE was found in all strains (100%). SitC (89.1%), ssaR (83.9%), sipA (70.1%), sipD (73.0%), sopE2 (68.6%), spvC (68.6%) and pefA (73.0%) were also highly prevalent. Noticeable differences were observed between serovars in terms of sopE2, spvC and pefA prevalence: 77.1%, 80% and 82.9%, respectively, of S. Enteritidis strains were sopE2, spvC and pefA positive while 40.6%, 31.3% and 40.6% of S. Typhimurium strains were positive. This finding indicates that S. Enteritidis is more frequent than S. Typhimurium in poultry populations thanks to higher virulence. Based on virulence gene distribution, the strains were divided into 44 different virulence genotypes, with the major genotype 4 (15.3%) carrying 8 of the 11 genes. The majority of strains (75.9%) were positive for at least 6 genes. S. Enteritidis and S. Typhimurium strains were highly virulent and pose a threat as a zoonotic infection.

Molecular Detection of Virulence Factors in Salmonella serovars Isolated from Poultry and Human Samples

Salmonellosis is a common infectious disease in humans caused by Salmonella spp., which in recent years has shown an increase in its incidence, with products of avian origin being a common source of transmission. To present a successful infective cycle, there are molecular mechanisms such as virulence factors that provide characteristics that facilitate survival, colonization, and damage to the host. According to this, the study aims to characterize the virulence factors of Salmonella spp. strains isolated from broilers (n = 39) and humans (n = 10). The presence of 24 virulence genes was evaluated using end-point PCR. All the strains of Salmonella spp. isolated from broiler chickens revealed presence of 7/24 (29, 16%) virulence genes (lpfA, csgA, sitC, sipB, sopB, sopE, and sivH). Regarding the strains isolated from cases of gastroenteritis in humans, all strains contained (14/24, 58, 33%) virulence genes (lpfA, csgA, pagC, msgA, spiA, sitC, iroN, sipB, orgA, hilA, sopB, sifA, avrA, and sivH). In summary, the presence of virulence genes in different strains of Salmonella isolated from broilers and humans could be described as bacteria with potential pathogenicity due to the type and number of virulence genes detected. These findings are beneficial for the pathogenic monitoring of Salmonella in Colombia.

Lacticaseibacillus rhamnosus alleviates intestinal inflammation and promotes microbiota-mediated protection against Salmonella fatal infections

The fatal impairment of the intestinal mucosal barrier of chicks caused by Salmonella significantly resulting economic losses in the modern poultry industry. Probiotics are recognized for beneficially influencing host immune responses, promoting maintenance of intestinal epithelial integrity, antagonistic activity against pathogenic microorganisms and health-promoting properties. Some basic studies attest to probiotic capabilities and show that Lacticaseibacillus rhamnosus could protect intestinal mucosa from injury in animals infected with Salmonella Typhimurium. However, the mechanisms underlying its protective effects in chicks are still not fully understood. Here, we used the chick infection model combined with histological, immunological, and molecular approaches to address this question. The results indicated that L. rhamnosus significantly reduced the diarrhea rate and increased the daily weight gain and survival rate of chicks infected with S. Typhimurium. Furthermore, we found that L. rhamnosus markedly improved the immunity of gut mucosa by reducing apoptotic cells, hence effectively inhibiting intestinal inflammation. Notably, pre-treatment chicks with L. rhamnosus balanced the expression of interleukin-1β and interleukin-18, moderated endotoxin and D-lactic acid levels, and expanded tight junction protein levels (Zonula occluden-1 and Claudin-1), enhanced the function of the intestinal mucosal epithelial cells. Additionally, investigations using full-length 16S rRNA sequencing also demonstrated that L. rhamnosus greatly weakened the adhesion of Salmonella, the mainly manifestation is the improvement of the diversity of intestinal microbiota in infected chicks. Collectively, these results showed the application of L. rhamnosus against Salmonella fatal infection by enhancing barrier integrity and the stability of the gut microbiota and reducing inflammation in new hatch chicks, offering new antibiotic alternatives for farming animals.

Seroprevalence of pullorum disease in chicken across mainland China from 1982 to 2020: A systematic review and meta-analysis

Pullorum disease (PD), caused by the bacterium Salmonella pullorum, severely threatens the health of chickens worldwide, especially in China, and generating concerns for public health safety. Greater awareness of the seroprevalence may facilitate the prevention and control of this disease. We conducted systematic review and meta-analysis on the seroprevalence of PD in chicken flocks across mainland China. The results show that the overall pooled estimates of PD seroprevalence in chicken flocks was 18.2%. Furthermore, during 38-year period the seroprevalence of PD was markedly high in all seven regions, being at least 14.9% in central China. Our results suggest PD was highly prevalent in autumn, followed by winter. Chickens older than 120 days (22.6%, CI₉₅: 14.5%-31.9%) had a significantly higher positive rate of PD than those <120 days in age (9.4%, CI₉₅: 3.7%-17.4%). Additionally, the rearing mode used is a risk factor associated with the seroprevalence of PD, it being considerably lower for caged chickens (13.7%, CI₉₅: 7.1%-22.0%) than free-range chickens (30.4%, CI₉₅: 17.3-45.4%). Our findings demonstrate that PD still poses a major threat to poultry industries in mainland China, and therefore comprehensive and stringent strategies are needed to prevent and control this disease.

Emergence, Dissemination and Antimicrobial Resistance of the Main Poultry-Associated Salmonella Serovars in Brazil

Salmonella infects poultry, and it is also a human foodborne pathogen. This bacterial genus is classified into several serovars/lineages, some of them showing high antimicrobial resistance (AMR). The ease of Salmonella transmission in farms, slaughterhouses, and eggs industries has made controlling it a real challenge in the poultry-production chains. This review describes the emergence, dissemination, and AMR of the main Salmonella serovars and lineages detected in Brazilian poultry. It is reported that few serovars emerged and have been more widely disseminated in breeders, broilers, and layers in the last 70 years. Salmonella Gallinarum was the first to spread on the farms, remaining as a concerning poultry pathogen. Salmonella Typhimurium and Enteritidis were also largely detected in poultry and foods (eggs, chicken, turkey), being associated with several human foodborne outbreaks. Salmonella Heidelberg and Minnesota have been more widely spread in recent years, resulting in frequent chicken/turkey meat contamination. A few more serovars (Infantis, Newport, Hadar, Senftenberg, Schwarzengrund, and Mbandaka, among others) were also detected, but less frequently and usually in specific poultry-production regions. AMR has been identified in most isolates, highlighting multi-drug resistance in specific poultry lineages from the serovars Typhimurium, Heidelberg, and Minnesota. Epidemiological studies are necessary to trace and control this pathogen in Brazilian commercial poultry production chains.

The activity of Meniran (Phyllanthus niruri Linn.) extract on Salmonella pullorum infected broilers

Background and Aim: Pullorum is an acute and chronic disease caused by Salmonella pullorum, often infecting chicken farms. Pullorum disease treatment using antibiotics that do not follow the control dose can cause bacteria to become antibiotic-resistant. Meniran contributes to inhibiting and antagonizing bacteria and can increase the efficiency of chicken feed because of its bioactive compounds, including alkaloids, flavonoids, tannins, and saponins. This study aimed to determine the activity of Meniran extract (Phyllanthus niruri Linn.) in broilers infected with S. pullorum. Materials and Methods: In vitro study that was conducted includes phytochemical test, diffusion, and dilution methods using Meniran extract at 5%, 10%, 20%, and 40% concentrations and tylosin at 2% concentration. The data of the dilution method (minimum inhibitory concentration [MIC] and minimum bactericidal concentration [MBC]) were processed using probit analysis to determine LC50. In vivo study was conducted by randomly dividing 20 broilers into five treatment groups, four per group. The chickens (except in group P0–) were infected with S. pullorum aged 14 days. Then, the treatment was conducted according to the divided groups when the chickens were aged 21-34 days. The said treatments are P0– (uninfected S. pullorum and unadministered with Meniran extract), P0+ (infected with S. pullorum and unadministered with Meniran extract), and P1, P2, and P3 (infected with S. pullorum and administered with Meniran extract with 5%, 10%, and 20% concentrations, respectively). Data from the phytochemical test were analyzed as descriptive. The data from the diffusion method were analyzed using one-way analysis of variance (ANOVA) and Duncan's test. Then, the results of broilers' performance were analyzed using ANOVA and Duncan's test. Results: The phytochemical test showed positive for alkaloid, tannin, saponin, flavonoid, and steroid/triterpenoid. The diffusion method formed the largest zone at 40% concentration with 15.6 mm, while 20%, 10%, and 5% had average of 13.15 mm, 8.38 mm, and 5.8 mm, respectively. The dilution method (MIC and MBC) exhibited the antibacterial ability of Meniran extract against S. pullorum at 20% dose and LC50 14.118% concentration. The Meniran extract administration in broilers exhibited improved performance of chickens infected with S. pullorum, with the administration of 20% dose of Meniran extract showing the best result. Conclusion: About 20% concentration Meniran extract can serve as an antibacterial agent and showed the best results in broilers infected with S. pullorum.

Safety and protective efficacy of Salmonella Pullorum spiC and rfaH deletion rough mutant as a live attenuated DIVA vaccine candidate

Salmonella enterica serovar Pullorum (S. Pullorum) causes pullorum disease (PD), which is an acute systemic disease, in chickens, and leads to serious economic losses in many developing countries because of its high morbidity and mortality rate in young chicks. The live-attenuated vaccine is considered to be an effective measure to control the Salmonella infection. In addition, the DIVA (differentiation of infected and vaccinated animals) feature without the interference of serological monitoring of Salmonella infection is an important consideration in the development of the Salmonella vaccine. In this study, we evaluated the immunogenicity and protective efficacy of a S. Pullorum rough mutant S06004ΔspiCΔrfaH as a live attenuated DIVA vaccine candidate in chickens. The S06004ΔspiCΔrfaH exhibited a significant rough lipopolysaccharides (LPS) phenotype which was agglutinated with the acriflavine, not with the O₉ mono antibody. Compared to the wild-type, 50% lethal dose (LD₅₀) of the rough mutant increased 100-fold confirmed its attenuation. The mutant strain also showed a decreased bacterial colonization in the spleen and liver. The immunization with the mutant strain had no effect on the body weight and no tissue lesions were observed in the liver and spleen. The high level of the S. Pullorum-specific IgG titers in the serum indicated that significant humoral immune responses were induced in the immunization group. The cellular immune responses were also elicited from the analysis of lymphocyte proliferation and expression of cytokines in the spleen. In addition, the S06004ΔspiCΔrfaH immunized group exhibited a negative response for the serological test, while the wild-type S06004 infection group was strongly positive for the serological test showing a DIVA capability. The survival rates in the vaccinated chickens were 87% after intramuscular challenge with wild-type S. Pullorum, while the survival rates were 20% in the control groups. Overall, these results have demonstrated that the rough mutant S06004ΔspiCΔrfaH strain can be developed as an efficient live attenuated DIVA vaccine candidate to control the systemic S. Pullorum infection without the interference of salmonellosis monitoring program in poultry.

Virulence Comparison of Salmonella enterica Subsp. enterica Isolates from Chicken and Whole Genome Analysis of the High Virulent Strain S. Enteritidis 211

Background: Salmonellaenterica is one of the common pathogens in both humans and animals that causes salmonellosis and threatens public health all over the world. Methods and Results: Here we determined the virulence phenotypes of nine Salmonellaenterica subsp. enterica (S. enterica) isolates in vitro and in vivo, including pathogenicity to chicken, cell infection, biofilm formation and virulence gene expressions. S. Enteritidis 211 (SE211) was highly pathogenic with notable virulence features among the nine isolates. The combination of multiple virulence genes contributed to the conferring of the high virulence in SE211. Importantly, many mobile genetic elements (MGEs) were found in the genome sequence of SE211, including a virulence plasmid, genomic islands, and prophage regions. The MGEs and CRISPR-Cas system might function synergistically for gene transfer and immune defense. In addition, the neighbor joining tree and the minimum spanning tree were constructed in this study. Conclusions: This study provided both the virulence phenotypes and genomic features, which might contribute to the understanding of bacterial virulence mechanisms in Salmonella enterica subsp. enterica. The first completed genomic sequence for the high virulent S. Enteritidis isolate SE211 and the comparative genomics and phylogenetic analyses provided a preliminary understanding of S. enterica genetics and laid the foundation for further study.

Virulence Variation of Salmonella Gallinarum Isolates through SpvB by CRISPR Sequence Subtyping, 2014 to 2018

Simple Summary

Salmonella Gallinarum causes fowl typhoid in all ages of chickens, which results in economic loss of commercial chicken farms. The disease has been eradicated in many developed countries, but is still prevalent in Korea. In this study, we investigated virulence and genetic variation of S. Gallinarum from Korea, between 2014 and 2018. The results indicated that virulence was increased, which was associated with genetic change over time. Therefore, surveillance of genetic change associated with virulence increase is necessary for monitoring of S. Gallinarum isolates for dissemination.

Abstract

Salmonella Gallinarum is a Gram-negative bacteria that causes fowl typhoid, a septicemic disease with high morbidity and mortality that affects all ages of chickens. Although vaccines and antimicrobials have been used nationwide to eradicate the disease, the malady is still prevalent in Korea. In this study, we investigated the virulence and genetic variation of 116 S. Gallinarum isolates from laying hens between 2014 and 2018. A total of 116 isolates were divided into five Gallinarum Sequence Types (GST) through clustered regularly interspaced short palindromic repeats (CRISPR) subtyping method. The GSTs displayed changes over time. The 116 isolates showed no difference in virulence gene distribution, but the polyproline linker (PPL) length of the SpvB, one of the virulence factors of Salmonella spp., served as an indicator of S. Gallinarum pathogenicity. The most prevalent PPL length was 22 prolines (37.9%). The shortest PPL length (19 prolines) was found only in isolates from 2014 and 2015. However, the longest PPL length of 24 prolines appeared in 2018. This study indicates that PPLs of S. Gallinarum in Korea tend to lengthen over time, so the pathogenic potency of the bacteria is increasing. Moreover, the transition of GST was associated with PPL length extension over time. These results indicate that surveillance of changing GST and PPL length are necessary in the monitoring of S. Gallinarum isolates.

An Outbreak of Pullorum Disease in a Young Layer Parent Flock in Austria Presented with Central Nervous System Signs

The present report describes an outbreak of Pullorum disease in a young layer parent stock in Austria. The flock, which comprised 14,220 Lohmann brown layer chickens, experienced high mortality from the first week of life, reaching a total of 1905 chickens in the fifth week, when the flock was depopulated. Clinical signs included uneven size of the chicks, pasty vents, apathy, and diminished water and feed intake, with some birds presenting central nervous system signs such as tremors and torticollis. The postmortem investigation of 43 birds, of ages 1 to 4 weeks, revealed retained yolk sacs filled with caseous exudate, purulent airsacculitis, hepatitis with whitish pinpoint coalescing necrotic foci, splenitis with splenomegaly, hemorrhagic-mucoid enteritis in the small intestine, fibrinous typhlitis, nephromegaly, and urate deposits in the ureters and cloaca. Inflammation and/or necrosis were identified in liver, spleen, kidney, small intestine, and heart by histopathology. However, no histopathologic lesions were observed in the brain. Salmonella enterica was isolated from heart, liver, spleen, and brain in pure culture. Group-specific serotyping determined the presence of group D, with S. enterica subspecies enterica serovar Gallinarum being confirmed based on the Kauffmann-White scheme. A duplex PCR further identified S. enterica subspecies enterica serovar Gallinarum biovar Pullorum as the responsible agent for the outbreak. Subsequently, the grandparent flocks, from which the affected flock originated, were tested and found to be negative for Salmonella Pullorum, with no other progenies from the same grandparents developing disease. Although the source of the pathogen could not be identified, such findings highlight the importance of "old" pathogens such as Salmonella Pullorum causing sudden high mortality in chicks, even in a highly controlled environment.

Evaluation of young chickens challenged with aerosolized Salmonella Pullorum

Salmonella enterica serovar Pullorum (S. Pullorum) is an important pathogen specific to avian species, which poses a serious threat to the poultry industry. The transmission of S. Pullorum occurs both horizontally and vertically but the airborne transmission of S. Pullorum has been neglected historically. In this study, the effects of aerosolized S. Pullorum on young chickens were investigated. The results showed that the colonization and morbidity induced by bioaerosol infection are dose dependent. The bacteria colonized in chicken lung for more than 14 days following the exposure to ≥ 1.25 × 10⁶ CFU/m³ of aerosolized S. Pullorum. Tachypnoea and depression were present in all the chickens between 5 and 7 days after infection, and some died, following the exposure to ≥1.25 × 10⁸ CFU/m³ of aerosolized S. Pullorum. RT-PCR results showed that significant expressions of inflammatory cytokines, including tumour necrosis factor α, interleukin 1β (IL-1β), IL-6, and IL-8 were noted in the lung and spleen. Histopathological examination showed lung swelling, with obvious lesions, including inflammatory cell infiltration, tissue injury, and acute haemorrhage. These results suggest that uncontrolled and detrimental inflammation is caused by a high dose of aerosolized S. Pullorum. These results further extend our understanding of the pathogenicity of air-transmitted S. Pullorum on chickens. RESEARCH HIGHLIGHTS Aerosolized S. Pullorum caused tachypnoea, depression, and lung swelling in chickens. The colonization and morbidity caused by aerosolized S. Pullorum are dose dependent. Detrimental inflammation is caused by high doses of aerosolized S. Pullorum in lung.

Occurrence and Characterization of Salmonella Isolated From Chicken Breeder Flocks in Nine Chinese Provinces

We investigated the prevalence of salmonellosis on 17 poultry breeding farms in nine Chinese provinces (Shandong, Jiangsu, Anhui, Zhejiang, Fujian, Guangdong, Yunnan, Sichuan, and Chongqing). Altogether, 3,508 samples from poultry breeding farms were collected in 2019, including 1,400 from cloaca swabs, 210 from feed, 1,688 from chicken embryos, and 210 from water. All the samples were subjected to bacterial isolation and culture, and bacterial species were identified by polymerase chain reaction. Serotyping, multilocus sequence typing (MLST), and drug-resistance phenotyping were performed on the isolates identified as Salmonella. Altogether, 126 Salmonella strains were detected in the 3,508 samples and the positivity rate for the samples was 3.59%. Among all the strains, 95 Salmonella isolates were selected for antimicrobial susceptibility test, resistance gene detection, serotyping, and genotyping. S. gallinarum-pullorum (57/95, 60.00%), S. enteritidis (22/95, 23.16%), and S. agona (16/95, 16.84%) serotypes were identified. The MLST classification showed that the 95 Salmonella strains fell into the following five sequence types (STs): ST92 (37/95, 38.95%), ST11 (22/95, 23.16%), ST2151 (19/95, 20.00%), ST13 (16/95, 16.84%), and ST470 (1/95, 1.05%). Apart from ST13, the other four STs shared close genetic relationships, and the genetic direction was ST11-ST470-ST92-ST2151. The resistance rates in the 95 isolates were 100% (95/95) for erythromycin, 68.42% (65/95) for tetracycline, and 53.68% (51/95) for streptomycin and ampicillin, respectively. The isolates were sensitive to polymyxin and sulfamethoxazole. Multi-drug resistance was seen in 70.53% (67/95) of the isolates. β-lactam-, aminoglycoside- and sulfonamide-encoding resistance genes were detected by PCR. The detection rate for bla _TEM and sul3 was 100% (95/95), whereas sul2 and aaC4 had rates of 52.63 and 23.16%, respectively. These results indicate that some of the salmonellosis seen in Chinese breeding chicken farms may be caused by infection with S. gallinarum-pullorum, S. enteritidis, and S. agona. They also show that some Salmonella isolates have multi-drug resistance phenotypes and carry multi-drug resistance genes.