Advances in vaccination against avian pathogenic Escherichia coli respiratory disease: potentials and limitations

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.

Vaccinating parent flocks against colibacillosis reduces broiler mortality - A retrospective observational study from 2016 to 2019 in Finland

Colibacillosis is one of the most important infectious diseases in modern poultry production. The complex nature of colibacillosis has made it challenging to produce an effective vaccine. As a control measure for colibacillosis outbreak in Finland, a vaccination program with a commercial colibacillosis vaccine and later also an autogenous vaccine was started for parent flocks in 2017. In this retrospective observational study from years 2016-2019, we evaluated first week and total mortality of broiler flocks (n= 6969) originating from parents with different colibacillosis vaccination status. Broiler flocks were divided into three groups according to vaccination status of their parent flocks. First group were flocks from parents with no colibacillosis vaccines; second group was flocks from parents vaccinated with commercial vaccine only; and third group was flocks from parents with both commercial and autogenous vaccine. Bayesian modelling was used to predict posterior distributions of first week mortality and total mortality of the broiler flocks. Results of the modelling revealed that broiler flocks from unvaccinated parents had the highest mortality rates (mean first week mortality 1.40 % and mean total mortality 4.33 %, respectively) whereas flocks from parents with a combination of commercial and autogenous vaccinations had the lowest mortality rates (mean first week mortality 0,91 % and mean total mortality 3,14 %). The mortalities from broilers flocks from parents with only commercial vaccine fell in between these groups. Also, standard deviations of mortality rates were lower in broilers from parents with commercial or both vaccines. This demonstrates that in addition to lowering the mean mortality rates, the vaccinations made high mortality broiler flocks less common. Best performance was obtained when autogenous vaccine was combined to the commercial vaccine. The autogenous vaccine consists of the same type of Escherichia coli strain that was causing most colibacillosis cases during the study period in Finland. This study adds to the evidence of benefits of colibacillosis vaccines during outbreaks. It also demonstrates the importance of the knowledge of the types of APEC strains causing outbreaks to produce effective autogenous vaccines.

Isolation and identification of specific Enterococcus faecalis phage C-3 and G21-7 against Avian pathogenic Escherichia coli and its application to one-day-old geese

Colibacillosis caused by Avian pathogenic Escherichia coli (APEC), including peritonitis, respiratory tract inflammation and ovaritis, is recognized as one of the most common and economically destructive bacterial diseases in poultry worldwide. In this study, the characteristics and inhibitory potential of phages were investigated by double-layer plate method, transmission electron microscopy, whole genome sequencing, bioinformatics analysis and animal experiments. The results showed that phages C-3 and G21-7 isolated from sewage around goose farms infected multiple O serogroups (O1, O2, O18, O78, O157, O26, O145, O178, O103 and O104) Escherichia coli (E.coli) with a multiplicity of infection (MOI) of 10 and 1, respectively. According to the one-step growth curve, the incubation time of both bacteriophage C-3 and G21-7 was 10 min. Sensitivity tests confirmed that C-3 and G21-6 are stable at 4 to 50 °C and pH in the range of 4 to 11. Based on morphological and phylogenetic analysis, phages C-3 and G21-7 belong to Enterococcus faecalis (E. faecalis) phage species of the genus Saphexavirus of Herelleviridae family. According to genomic analysis, phage C-3 and G21-7 were 58,097 bp and 57,339 bp in size, respectively, with G+C content of 39.91% and 39.99%, encoding proteins of 97 CDS (105 to 3,993 bp) and 96 CDS (105 to 3,993 bp), and both contained 2 tRNAs. Both phages contained two tail proteins and holin-endolysin system coding genes, and neither carried resistance genes nor virulence factors. Phage mixture has a good safety profile and has shown good survival probability and feed efficiency in both treatment and prophylaxis experiments with one-day-old goslings. These results suggest that phage C-3 and G21-7 can be used as potential antimicrobials for the prevention and treatment of APEC.

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.

Unveiling the traits of antibiotic resistance and virulence in Escherichia coli obtained from poultry waste

Antibiotic resistance and virulence factors in avian pathogenic Escherichia coli (APEC) have become significant concerns, contributing to adverse environmental effects. The extensive use of antibiotics in poultry farming has resulted in the emergence of antibiotic-resistant APEC strains. This study prioritizes the molecular screening of APEC to uncover their antibiotic resistance and virulence attributes, with specific attention to their environmental impact. To address the imperative of understanding APEC pathogenesis, our study analyzed 50 poultry waste samples including 10 poultry litter, 15 fecal matter, 15 wastewater, and 10 anatomical waste samples. For the presence of virulence genes, 35 Escherichia coli isolates were subjected to molecular characterization. Amongst these, 27 were APEC strains demonstrating the presence of at least four virulence genes each. Notably, virulence genes such as fimH, ompA, ybjX, waaL, cvaC, hlyF, iss, ompT, and iroN were observed among all the E. coli isolates. Furthermore, eleven of the APEC strains exhibited resistance to tetracycline, ampicillin, sulphonamides, and fluoroquinolones.These findings highlight the role of APEC as a potential source of environmental pollution serving as a reservoir for virulence and resistance genes. Understanding the dynamics of antibiotic resistance and virulence in APEC is essential due to its potential threat to broiler chickens and the broader population through the food chain, intensifying concerns related to environmental pollution. Recognizing the ecological impact of APEC is essential for developing effective strategies to mitigate environmental pollution and safeguard the health of ecosystems and human populations.

Comparison of the safety and efficacy of the wild-type and lpxL/lpxM mutant inactivated vaccine against the avian pathogenic Escherichia coli O1, O2, and O78 challenge

Avian pathogenic Escherichia coli (APEC) is primarily responsible for causing septicemia, pneumonitis, peritonitis, swollen head syndrome, and salpingitis in poultry, leading to significant losses in the poultry sector, particularly within the broiler industry. The removal of the lpxL and lpxM genes led to an eightfold decrease in the endotoxin levels of wild APEC strains. In this study, mutant strains of lpxL/lpxM and their O1, O2, and O78 wild-type strains were developed for an inactivated vaccine (referred to as the mutant vaccine and the wild-type vaccine, respectively), and the safety and effectiveness of these two prototype vaccines were assessed in white Leghorn chickens. Findings indicated that chickens immunized with the mutant vaccine showed a return of appetite sooner post-immunization and experienced earlier disappearance of nodules at the injection site compared to those immunized with the wild-type vaccine. Pathological examinations revealed that lesions were still present in the liver, lung, and injection site in chickens vaccinated with the wild-type vaccine 14 days post-vaccination (dpv), whereas no lesions were found in chickens vaccinated with the mutant vaccine at 14 dpv. There were no significant differences in antibody levels on the challenge day or in mortality or lesion scores between challenged birds immunized with either the mutant vaccine or the wild-type vaccine at the same dose. In this study, the safety of a single dose or overdose of the mutant vaccine and its efficacy at one dose were evaluated in broilers, and the results showed that the mutant vaccine had no adverse effects on or protected vaccinated broilers from challenge with the APEC O1, O2, or O78 strains. These results demonstrated that the mutant polyvalent inactivated vaccine is a competitive candidate against APEC O1, O2, and O78 infection compared to the wild-type vaccine.

Combined analysis of the microbiome, metabolome and transcriptome of silkie chickens in response to avian pathogenic E. coli (APEC)

Avian colibacillosis is a bacterial disease caused by avian pathogenic Escherichia coli (APEC) that results in great losses in the poultry industry every year. Individual Silkie chickens of the same breed that are given the same feed in the same feeding conditions have different levels of resistance or susceptibility to APEC. Differences in gut microbes, gut metabolites, and gene expression in the spleen of APEC-resistant and APEC-susceptible chickens were compared, and multiple omics associations were analyzed to explore the mechanism of resistance to APEC in Silkie chickens. Compared with those in the APEC-susceptible group, the APEC-resistant group showed significantly increased abundances of many gut microorganisms, including Bacillus, Thermoactinomyces, Arthrobacter, and Ureibacillus, which were positively correlated with norvaline, l-arginine, and valyl-glycine levels. Intestinal tryptophan, indole, and indole derivative-related differentially abundant metabolites played an active role in combatting APEC infection. In the spleen, "response to stimulus" was the most significantly enriched GO term, and "cytokine‒cytokine receptor interaction" was the most significantly enriched KEGG pathway. The arginine biosynthesis and PPAR signaling pathways were the KEGG pathways that were significantly enriched with differentially abundant metabolites and differentially expressed genes. This study provides new insight into the prevention and treatment of APEC infection in Silkie chickens and lays a foundation to study the mechanism of APEC infection in poultry.

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.

Differential responses to avian pathogenic E. coli and the regulatory role of splenic miRNAs in APEC infection in Silkie chickens

Avian pathogenic Escherichia coli (APEC) is a bacterial disease that harms the poultry industry worldwide, but its effect on Chinese Silkie has not been reported. Studies on whether there are differences in Silkie individual resistance to APEC and the regulatory role of spleen miRNAs lay the foundation for strategies against APEC. Therefore, 270 Silkie chickens were infected with the median lethal dose of an E. coli O1, O2, and O78 mixture. These chickens were divided into a susceptible group (Group S) and a recovery group (Group R) according to whether they survived 15 days postinfection (dpi). Moreover, 90 uninfected APEC Silkie served as controls (Group C). The splenic miRNA expression profile was examined to evaluate the role of miRNAs in the APEC infection response. Of the 270 Silkies infected with APEC, 144 were alive at 15 dpi. Cluster analysis and principal component analysis (PCA) of splenic miRNAs revealed that the four Group R replicates were clustered with the three Group C replicates and were far from the three Group S replicates. Differentially expressed (DE) miRNAs, especially gga-miR-146b-5p, play essential roles in immune and inflammatory responses to APEC. Functional enrichment analyses of DEmiRNAs suggested that suppression of immune system processes (biological processes) might contribute to susceptibility to APEC and that FoxO signaling pathways might be closely associated with the APEC infection response and postinfection repair. This study paves the way for screening anti-APEC Silkies and provides novel insights into the regulatory role of miRNAs in APEC infection.

Virulome analysis of Escherichia coli ST117 from bovine sources identifies similarities and differences with strains isolated from other food animals

Escherichia coli ST117 is a pandemic extraintestinal pathogenic E. coli (ExPEC) causing significant morbidity globally. Poultry are a known reservoir of this pathogen, but the characteristics of ST117 strains from other animal sources have not been adequately investigated. Here we characterize the genomes of 36 ST117 strains recovered primarily from preweaned dairy calves, but also from older postweaned calves and lactating cows, in the context of other bovine-associated strains and strains from poultry, swine, and humans. Results of this study demonstrate that bovine-associated ST117 genomes encode virulence factors (VFs) known to be involved in extraintestinal infections, but also occasionally encode the Shiga toxin, a virulence factor (VF) involved in severe gastrointestinal infections and more frequently identified in E. coli from ruminants than other animals. Bovine-associated ST117 genomes were also more likely to encode afa-VIII (adhesins), pap (P-fimbriae), cdt (cytolethal distending toxin), and stx (Shiga toxins) than were poultry and swine-associated genomes. All of the ST117 genomes were grouped into seven virulence clusters, with bovine-associated genomes grouping into Clusters 1, 2, 4, 5, but not 3, 6, or 7. Major differences in the presence of virulence factors between clusters were observed as well. Antimicrobial resistance genes were detected in 112 of 122 (91%) bovine-associated genomes, with 103 of these being multidrug-resistant (MDR). Inclusion of genomes that differed from ST117 by one multi-locus sequence type (MLST) allele identified 31 STs, four of these among the bovine-associated genomes. These non-ST117 genomes clustered with the ST117 genomes suggesting that they may cause similar disease as ST117. Results of this study identify cattle as a reservoir of ST117 strains, some of which are highly similar to those isolated from other food animals and some of which have unique bovine-specific characteristics.

Veterinary Autogenous Vaccines for Poultry in Europe-Many Ways to Crack an Egg

In the past decade, European animal farming has increasingly used autogenous vaccines for the prevention of nonnotifiable diseases. In Europe, these vaccines are exclusively inactivated bacterial and viral vaccines, with a set of specific regulations that differentiate them from conventional vaccines. The highest number of applications most likely occurs in poultry, as these animal species are farmed in the highest numbers compared with other types of food-producing animals. In 2019, autogenous vaccines came within the scope of harmonized European regulation for the first time, although many important aspects are still missing and need to be further developed. Consequently, several important legal provisions remain in national legislations and can vary tremendously between different member states of the European Union. The inclusion of autogenous vaccines in the management of certain diseases of poultry is justified by the nonavailability of licensed vaccines and the evolution and diversity of antigens in the field that are not covered by licensed vaccines. In addition, these vaccines aid in reducing the use of antibiotics. The methods for isolating and typing pathogenic isolates to obtain relevant antigens are pathogen specific and require a careful approach based on clinical evidence. Manufacturing processes are optimized according to regulatory standards, and they represent the most critical factor influencing the quality of autogenous vaccines and their placement on the market. This review presents the important requirements for manufacturing autogenous vaccines for poultry in addition to the relevant regulatory considerations. The results from a survey of several European Union member states regarding specific provisions within their national legislations are also presented.

Analysis of alternative splicing in chicken macrophages infected with avian pathogenic E. coli (APEC)

Colibacillosis is a complex disease that caused by avian pathogenic Escherichia coli (APEC), resulting in huge economic loss to the global poultry industry and threatening to human health. Alternative splicing (AS) is a universal post-transcriptional regulatory mechanism, which can simultaneously produce many proteins from a single gene to involve in various diseases and individual development. Herein, we characterized genome-wide AS events in wild type macrophages (WT) and APEC infected macrophages (APEC) by high-throughput RNA sequencing technology. A total of 751 differentially expressed (DE) AS genes were identified in the comparison of APEC vs. WT, including 587 of SE, 114 of MXE, 25 of RI, 17 of A3 and 8 of A5 event. Functional analysis showed that these identified DE AS genes were involved in 'Endocytosis', 'p53 signaling pathway', 'MAPK signaling pathway', 'NOD-like receptor signaling pathway', 'Ubiquitin mediated proteolysis' and 'Focal adhesion' immune related pathways. In summary, we comprehensively investigate AS events during APEC infection. This study has expanded our understanding of the process of APEC infection and provided new insights for further treatment options for APEC infection.

Recombinant Salmonella gallinarum (S. gallinarum) Vaccine Candidate Expressing Avian Pathogenic Escherichia coli Type I Fimbriae Provides Protections against APEC O78 and O161 Serogroups and S. gallinarum Infection

Avian pathogenic Escherichia coli (APEC) is one of the leading pathogens that cause devastating economic losses to the poultry industry. Type I fimbriae are essential adhesion factors of APEC, which can be targeted and developed as a vaccine candidate against multiple APEC serogroups due to their excellent immunogenicity and high homology. In this study, the recombinant strain SG102 was developed by expressing the APEC type I fimbriae gene cluster (fim) on the cell surface of an avirulent Salmonella gallinarum (S. gallinarum) vector strain using a chromosome-plasmid-balanced lethal system. The expression of APEC type I fimbriae was verified by erythrocyte hemagglutination assays and antigen-antibody agglutination tests. In vitro, the level of the SG102 strain adhering to leghorn male hepatoma (LMH) cells was significantly higher than that of the empty plasmid control strain, SG101. At two weeks after oral immunization, the SG102 strain remained detectable in the livers, spleens, and ceca of SG102-immunized chickens, while the SG101 strain was eliminated in SG101-immunized chickens. At 14 days after the secondary immunization with 5 × 109 CFU of the SG102 strain orally, highly antigen-specific humoral and mucosal immune responses against APEC type I fimbriae protein were detected in SG102-immunized chickens, with IgG and secretory IgA (sIgA) concentrations of 221.50 μg/mL and 1.68 μg/mL, respectively. The survival rates of SG102-immunized chickens were 65% (13/20) and 60% (12/20) after challenge with 50 LD50 doses of APEC virulent strains O78 and O161 serogroups, respectively. By contrast, 95% (19/20) and 100% (20/20) of SG101-immunized chickens died in challenge studies involving APEC O78 and O161 infections, respectively. In addition, the SG102 strain effectively provided protection against lethal challenges from the virulent S. gallinarum strain. These results demonstrate that the SG102 strain, which expresses APEC type I fimbriae, is a promising vaccine candidate against APEC O78 and O161 serogroups as well as S. gallinarum infections.

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.

Complete genome sequence of an avian pathogenic Escherichia coli strain isolated from poultry

Avian pathogenic Escherichia coli found in the avian intestinal tract can cause systemic disease in birds and act as a foodborne zoonotic pathogen associated with human disease. Here, we report the complete genome sequence of E. coli strain H1998 isolated from a chicken with colisepticemia.

High resistance of fluoroquinolone and macrolide reported in avian pathogenic Escherichia coli isolates from the humid subtropical regions of Pakistan

OBJECTIVES

This study aimed to assess the antimicrobial resistance profile, virulence potential, and genetic characterization of avian pathogenic Escherichia coli (APEC) that cause colibacillosis in poultry.

METHODS

Antibiotic susceptibility testing (AST) was measured via the Kirby-Bauer disc diffusion method against 27 commonly used antibiotics. Phylogrouping, virulence-associated gene detection, and hybrid strain detection via multiplex polymerase chain reaction (PCR) and genetic diversity were analysed via ERIC-PCR fingertyping method.

RESULTS

AST analysis showed 100% of isolates were multidrug-resistant (MDR) and highest resistance was against penicillin, tetracycline, and macrolide classes of antibiotics. The mcr-1 gene was present in 40% of the isolates, though only 4% of isolates were showing phenotypic resistance. Despite the scarce use of fluoroquinolone, carbapenem, and cephalosporin in the poultry sector, resistance was evident because of the high prevalence of extended-spectrum β-lactamase (ESBL) (53.7%) and other β-lactamases in APEC isolates. β-lactamase genotyping of APEC isolates revealed that 85.7% of isolates contained either blaCTX or blaTEM and around 38% of isolates were complement resistant. Growth in human urine was evident in 67.3% of isolates. Phylogroup B1 (51%) was the most prevalent group followed by phylogroups A (30.6%), D (13.61%), and B2 (4.76%). The most prevalent virulence-associated genes were fimH, iss, and tatT. Results showed that 26 isolates (17.69%) can be termed hybrid strains and APEC/EHEC (enterohemorrhagic E. coli) was the most prevalent hybrid E. coli pathotype. ERIC-PCR fingerprinting genotype analysis clustered APEC isolates in 40 groups (E1-E40). This study provides insights into the antibiotic resistance and virulence profiling of the APEC isolates in Pakistan.

CONCLUSIONS

The findings of this study provide insights into that the antibiotic resistance and virulence profiling of the APEC isolates in Pakistan. This data can inform future studies designed to better estimate the severity of the colibacillosis in poultry farms.

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.

Umbilical Outpouchings in two Danish herds raising pigs with minimal use of antibiotics – Results from a field trial evaluating the efficacy of autogenous vaccines and iodine application

In Denmark, a Pure Pork concept for raising pigs without antibiotics was initiated in 2015 by the Danish Crown slaughterhouse cooperative. Pure Pork herds are characterised by minimal use of antibiotics and pigs are mainly treated individually. An increased prevalence of pigs suffering from umbilical outpouchings (UO) is a considerable challenge for Pure Pork producers. Umbilical outpouchings in pigs are challenging due to reduced welfare and increased workload and cost for the farmer. Therefore, Pure Pork producers require means other than antibiotic treatment to prevent UO. The primary objective of this study was therefore to evaluate the effect of autogenous sow vaccines based on bacteria isolated from the inflamed umbilici of piglets and a 7% iodine treatment at birth on the risk of pigs developing UO during the first 12 weeks of life. In addition, umbilical clinical and necropsy findings were presented, including variation over time and an identification of risk factors. A total of 5852 live-born piglets were included at birth from two Pure Pork herds. In this study, UO was defined as the presence of a rounded outpouching and/or a small firm protrusion at the umbilical area. Among 5614 pigs examined at weeks 5 and 12 and/or at death a total of 534 (9.5%) pigs were recorded with UO. The incidence of outpouchings was 10.2% for Herd A and 8.8% for Herd B. In the present field trial, neither autogenous vaccination of sows nor a 7% iodine spray on the umbilical area of new-born piglets had a statistically significant effect on the incidence of UO, but there was a tendency for a lower risk of UO in pigs treated with iodine spray at birth in one herd (OR = 0.7, p = 0.07), which might be worth investigating further. The risk factors for UO identified in this study included sow parity in one herd with more UO pigs from second parity sows and older compared to gilts (OR = 2.0, p = 0.02), batch in the second herd, and sex in both herds with male pigs at lower risk of UO development compared to female pigs (OR = 0.8, p = 0.006). Furthermore, antibiotic treatment as an indicator of the presence of other diseases resulted in a higher risk of UO compared to untreated pigs (OR = 1.9, p<0.0001). The presence of UO in one pig varied over time; For UO pigs examined alive at both week 5 and 12, 136 pigs (2.4%) had an UO record at week 5 but not at week 12 and 179 pigs (3.2%) did not have an UO at week 5 but a UO record at week 12. For 115 pigs (2.0%) an UO was recorded both at week 5 and week 12.

Integrated analysis of mRNA and microRNA expression pattern reveals differential transcriptome signatures in RIPK2 over-expressing chicken macrophages infected with avian pathogenic E. coli

1. As RIPK2 (receptor interacting serine/threonine kinase 2) has been shown to to alleviate excessive inflammatory responses, the following study conducted a systematic and in-depth analysis of the mRNA-seq and miRNA-seq data from chicken macrophages with/without over-expression of RIPK2 (oeRIPK2) combined with/without avian pathogenic E. coli (APEC) infection to identify the miRNA-mRNA interaction network and potential signalling pathways involved.2. A total of 9,201 differentially expressed (DE) mRNAs and 300 DE miRNA were identified in both oeRIPK2+APEC vs. APEC and oeRIPK2 vs. the wild-type (WT). Moreover, 4,269 instances of co-expression between miRNAs and mRNAs were seen involving 1,652 DE mRNAs and 164 DE miRNAs.3. Functional analysis of the DE mRNAs in the miRNA-mRNA interaction network showed that 223 biological processes and five KEGG pathways were significantly enriched in the two comparisons. In total, 128 pairs of miRNA-mRNA interactions were involved in the identified MAPK signalling pathway and focal adhesion immune related pathways.4. Significantly, these screened miRNAs (gga-miR-222b-5p and gga-miR-214) and their target genes were highly correlated with APEC infection and RIPK2. These recognised key genes, miRNA and the overall miRNA-mRNA regulatory network, enables better understanding of the molecular mechanism of host response to APEC infection, especially related to RIPK2.

Aerosol delivered irradiated Escherichia coli confers serotype-independent protection and prevents colibacillosis in young chickens

Escherichia coli causes colibacillosis in chickens, which has severe economic and public health consequences. For the first time, we investigated the efficacy of gamma-irradiated E. coli to prevent colibacillosis in chickens considering different strains and application routes. Electron microscopy, alamarBlue assay and matrix assisted laser desorption/ionization time-of- flight mass spectrometry showed that the cellular structure, metabolic activity and protein profiles of irradiated and non-treated E. coli PA14/17480/5-ovary (serotype O1:K1) were similar. Subsequently, three animal trials were performed using the irradiated E. coli and clinical signs, pathological lesions and bacterial colonization in systemic organs were assessed. In the first animal trial, the irradiated E. coli PA14/17480/5-ovary administered at 7 and 21 days of age via aerosol and oculonasal routes, respectively, prevented the occurrence of lesions and systemic bacterial spread after homologous challenge, as efficient as live infection or formalin-killed cells. In the second trial, a single aerosol application of the same irradiated strain in one-day old chickens was efficacious against challenges with a homologous or a heterologous strain (undefined serotype). The aerosol application elicited better protection as compared to oculonasal route. Finally, in the third trial, efficacy against E. coli PA15/19103-3 (serotype O78:K80) was shown. Additionally, previous results of homologous protection were reconfirmed. The irradiated PA15/19103-3 strain, which also showed lower metabolic activity, was less preferred even for the homologous protection, underlining the importance of the vaccine strain. In all the trials, the irradiated E. coli did not provoke antibody response indicating the importance of innate or cell mediated immunity for protection. In conclusion, this proof-of-concept study showed that the non-adjuvanted single aerosol application of irradiated "killed but metabolically active" E. coli provided promising results to prevent colibacillosis in chickens at an early stage of life. The findings open new avenues for vaccine production with E. coli in chickens using irradiation technology.

Efficacy of quorum sensing and growth inhibitors alone and in combination against avian pathogenic Escherichia coli infection in chickens

Avian pathogenic E. coli (APEC), a causative agent of colibacillosis, is associated with high mortality and morbidity which results in severe economic losses to the poultry industry worldwide. APEC can be transmitted to humans through the consumption of contaminated poultry products. The limited effect of the current vaccines and the advent of drug-resistant strains have necessitated the development of alternative therapies. Previously, we identified 2 small molecules (SMs; [quorum sensing inhibitor; QSI-5] and [growth inhibitor; GI-7]) with high efficacy in vitro and in chickens subcutaneously challenged with APEC O78. Here, we optimized the oral challenge dose of APEC O78 in chickens to mimic the infection in the natural settings, evaluated the efficacy of the GI-7, QSI-5, and combination of GI-7 and QSI-5 (GI7+ QSI-5) in chickens orally infected with APEC, and compared their efficacy to sulfadimethoxine (SDM), an antibiotic currently used to treat APEC. Using the optimized dose of each SM in drinking water, GI-7, QSI-5, GI7+ QSI-5, and SDM were evaluated in chickens challenged with the optimized dose of APEC O78 (1 × 10⁹ CFU/chicken; orally; d 2 of age) and grown on built-up floor litter. Reduction in mortality was 90, 80, 80, and 70% in QSI-5, GI-7+QSI-5, GI-7, and SDM treated groups compared to the positive control (PC), respectively. GI-7, QSI-5, GI-7+QSI-5, and SDM reduced the APEC load in the cecum by 2.2, 2.3, 1.6, and 0.6 logs and in the internal organs by 1.3, 1.2, 1.4, and 0.4 logs compared to PC (P < 0.05), respectively. The cumulative pathological lesions scores were 0.51, 0.24, 0.0, 0.53, and 1.53 in GI-7, QSI-5, GI-7+QSI-5, SDM, and PC groups, respectively. Overall, GI-7 and QSI-5 individually have promising effects as a potential antibiotic-independent approach to control APEC infections in chickens.

Identification of Subunits for Novel Universal Vaccines against Three Predominant Serogroups and the Emerging O145 among Avian Pathogenic Escherichia coli by Pan-RV Pipeline

Avian pathogenic Escherichia coli, a causative agent of avian colibacillosis, has been causing serious economic losses in the poultry industry. The increase in multidrug-resistant isolates and the complexity of the serotypes of this pathogen, especially the recently reported emergence of a newly predominant serogroup of O145, make the control of this disease difficult. To address this challenge, a high-throughput screening approach, called Pan-RV (Reverse vaccinology based on pangenome analysis), is proposed to search for universal protective antigens against the three traditional serogroups and the newly emerged O145. Using this approach, a total of 61 proteins regarded as probable antigens against the four important serogroups were screened from the core genome of 127 Avian pathogenic Escherichia coli (APEC) genomes, and six were verified by Western blots using antisera. Overall, our research will provide a foundation for the development of an APEC subunit vaccine against avian colibacillosis. Given the exponential growth of whole-genome sequencing (WGS) data, our Pan-RV pipeline will make screening of bacterial vaccine candidates inexpensive, rapid, and efficient. IMPORTANCE With the emergence of drug resistance and the newly predominant serogroup O145, the control of Avian pathogenic Escherichia coli is facing a serious challenge; an efficient immunological method is urgently needed. Here, for the first time, we propose a high-throughput screening approach to search for universal protective antigens against the three traditional serogroups and the newly emerged O145. Importantly, using this approach, a total of 61 proteins regarded as probable antigens against the four important serogroups were screened, and three were shown to be immunoreactive with all antisera (covering the four serogroups), thereby providing a foundation for the development of APEC subunit vaccines against avian colibacillosis. Further, our Pan-RV pipeline will provide immunological control strategies for pathogens with complex and variable genetic backgrounds such as Escherichia coli and will make screening of bacterial vaccine candidates more inexpensive, rapid, and efficient.

Evaluation of immunogenicity and efficacy of the enterobactin conjugate vaccine in protecting chickens from colibacillosis

Colibacillosis is one of the most common and economically devastating infectious diseases in poultry production worldwide. Innovative universal vaccines are urgently needed to protect chickens from the infections caused by genetically diverse avian pathogenic Escherichia coli (APEC). Enterobactin (Ent) is a highly conserved siderophore required for E. coli iron acquisition and pathogenesis. The Ent-specific antibodies induced by a novel Ent conjugate vaccine significantly inhibited the in vitro growth of diverse APEC strains. In this study, White Leghorn chickens were immunized with the Ent conjugate vaccine using a crossed design with two variables, vaccination (with or without) and APEC challenge (O1, O78, or PBS control), resulting in six study groups (9 to 10 birds/group). The chickens were subcutaneously injected with the vaccine (100 μg per bird) at 7 days of age, followed by booster immunization at 21 days of age. The chickens were intratracheally challenged with an APEC strain (10⁸ CFU/bird) or PBS at 28 days of age. At 5 days post infection, all chickens were euthanized to examine lesions and APEC colonization of the major organs. Immunization of chickens with the Ent vaccine elicited a strong immune response with a 64-fold increase in the level of Ent-specific IgY in serum. The hypervirulent strain O78 caused extensive lesions in lung, air sac, heart, liver, and spleen with significantly reduced lesion scores observed in the vaccinated chickens. Interestingly, the vaccination did not significantly reduce APEC levels in the examined organs. The APEC O1 with low virulence only caused sporadic lesions in the organs in both vaccination and control groups. The Ent conjugate vaccine altered the bacterial community of the ileum and cecum. Taken together, the findings from this study showed the Ent conjugate vaccine could trigger a strong specific immune response and was promising to confer protection against APEC infection.

Characteristics, pathogenic mechanism, zoonotic potential, drug resistance, and prevention of avian pathogenic Escherichia coli (APEC)

Although most Escherichia coli (E. coli) strains are commensal and abundant, certain pathogenic strains cause severe diseases from gastroenteritis to extraintestinal infections. Extraintestinal pathogenic E. coli (ExPEC) contains newborn meningitis E. coli (NMEC), uropathogenic E. coli (UPEC), avian pathogenic E. coli (APEC), and septicemic E. coli (SEPEC) based on their original host and clinical symptom. APEC is a heterogeneous group derived from human ExPEC. APEC causes severe respiratory and systemic diseases in a variety of avians, threatening the poultry industries, food security, and avian welfare worldwide. APEC has many serotypes, and it is a widespread pathogenic bacterium in poultry. In addition, ExPEC strains share significant genetic similarities and similar pathogenic mechanisms, indicating that APEC potentially serves as a reservoir of virulence and resistance genes for human ExPEC, and the virulence and resistance genes can be transferred to humans through food animals. Due to economic losses, drug resistance, and zoonotic potential, APEC has attracted heightened awareness. Various virulence factors and resistance genes involved in APEC pathogenesis and drug resistance have been identified. Here, we review the characteristics, epidemiology, pathogenic mechanism zoonotic potential, and drug resistance of APEC, and summarize the current status of diagnosis, alternative control measures, and vaccine development, which may help to have a better understanding of the pathogenesis and resistance of APEC, thereby reducing economic losses and preventing the spread of multidrug-resistant APEC to humans.

Inactivation of Airborne Avian Pathogenic E. coli (APEC) via Application of a Novel High-Pressure Spraying System

Infectious diseases of livestock caused by novel pathogenic viruses and bacteria are a major threat to global animal health and welfare and their effective control is crucial for agronomic health and for securing global food supply. It has been widely recognized that the transmission of infectious agents can occur between people and/or animals in indoor spaces. Therefore, infection control practices are critical to reduce the transmission of the airborne pathogens. ViKiller®-high-pressure sprayer and Deger®-disinfectant are newly developed spraying systems that can produce an optimal size of disinfectants to reduce airborne microbes. The system was evaluated to reduce the infection caused by avian pathogenic Escherichia coli (APEC), an airborne bacterium which survives in indoor spaces. pH-neutral electrolyzed water (NEW) containing 100 ppm of free chlorine, laboratory-scale chambers, a recently developed sprayer, and a conventional sprayer were used in the study. A total of 123 day-of-hatch male layer chicks (Hy-Line W-36) were randomly classified into five groups (negative control (NC): no treatment; treatment 1 (Trt 1): spraying only NEW without APEC; treatment 2 (Trt 2): spraying NEW + APEC using a high-pressure sprayer; treatment 3 (Trt 3): spraying NEW + APEC using a conventional sprayer; positive control (PC): spraying only APEC). Experimental chicks in the chambers were daily exposed to 50 mL of NEW and/or APEC (1.0 × 106 cfu/mL) until the end of the experiment (day 35). APEC strains were sprayed by ViKiller®. At least four chicks in each group were evaluated weekly to monitor APEC infection and determine the lesion. Data showed that our spraying system significantly reduced airborne APEC concentrations, mortality rate, respiratory infection, and APEC lesions in birds in the chamber space (p < 0.05). The results demonstrate that the antibacterial effect of the novel spraying sprayer with NEW on APEC was far superior compared to the conventional sprayer. This study provides a new insight for preventive measures against airborne microorganisms in indoor spaces.

Analysis of circRNA expression in chicken HD11 cells in response to avian pathogenic E.coli

Avian pathogenic E. coli (APEC), one of the widespread zoonotic-pathogen, can cause a series of diseases collectively known as colibacillosis. This disease can cause thousands of million dollars economic loss each year in poultry industry and threaten to human health via meat or egg contamination. However, the detailed molecular mechanism underlying APEC infection is still not fully understood. Circular RNAs, a new type of endogenous noncoding RNA, have been demonstrated to involve in various biological processes. However, it is still not clear whether the circRNAs participate in host response against APEC infection. Herein, we utilized the high-throughput sequence technology to identify the circRNA expression profiles in APEC infected HD11 cells. A total of 49 differentially expressed (DE) circRNAs were detected in the comparison of APEC infected HD11 cells vs. wild type HD11 cells, which were involved in MAPK signaling pathway, Endocytosis, Focal adhesion, mTOR signaling pathway, and VEGF signaling pathway. Specifically, the source genes (BRAF, PPP3CB, BCL2L13, RAB11A, and TSC2) and their corresponding DE circRNAs may play a significant role in APEC infection. Moreover, based on ceRNA regulation, we constructed the circRNA-miRNA network and identified a couple of important regulatory relationship pairs related to APEC infection, including circRAB11A-gga-miR-125b-3p, circRAB11A-gga-miR-1696, and circTSC2-gga-miR-1649-5p. Results indicate that the aforementioned specific circRNAs and circRNA-miRNA network might have important role in regulating host immune response against APEC infection. This study is the first time to investigate the circRNAs expression profile and the biological function of the source genes of the identified DE circRNAs after APEC infection of chicken HD11 cells. These results would contribute to a better understanding of the molecular mechanisms in host response against APEC infection.

Production of interferon gamma and interleukin 17A in chicken T-cell subpopulations hallmarks the stimulation with live, irradiated and killed avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) causes colibacillosis with different clinical manifestations. The disease is associated with compromised animal welfare and results in substantial economic losses in poultry production worldwide. So far, immunological mechanisms of protection against colibacillosis are not comprehensively resolved. Therefore, the present study aimed to use an ex vivo model applying chicken mononuclear cells stimulated by live and inactivated APEC. For this purpose, an 8-color flow cytometry panel was set up to target viable chicken immune cells including CD45⁺, CD8α⁺, CD4⁺, TCR-γδ⁺, Bu-1⁺ cells and monocytes/macrophages along with the cytokines interferon gamma (IFN-γ) or interleukin 17A (IL-17A). The 8-color flow cytometry panel was applied to investigate the effect of live and two different types of inactivated APEC (formalin-killed APEC and irradiated APEC) on the cellular immune response. For that, mononuclear cells from spleen, lung and blood of 10-week-old specific pathogen-free layer birds were isolated and stimulated with live, irradiated or killed APEC. Intracellular cytokine staining and RT-qPCR assays were applied for the detection of IFN-γ and IL-17A protein level, as well as at mRNA level for spleenocytes. Ex vivo stimulation of isolated splenocytes, lung and peripheral blood mononuclear cells (PBMCs) from chickens with live, irradiated or killed APEC showed an increasing number of IFN-γ and IL-17A producing cells at protein and mRNA level. Phenotyping of the cells from blood and organs revealed that IFN-γ and IL-17A were mainly produced by CD8α⁺, TCR-γδ⁺ T cells as well as CD4⁺ T cells following stimulation with APEC. Expression level of cytokines were very similar following stimulation with live and irradiated APEC but lower when killed APEC were applied. Consequently, in the present study, an ex vivo model using mononuclear cells of chickens was applied to investigate the cellular immune response against APEC. The results suggest the relevance of IFN-γ and IL-17A production in different immune cells following APEC infection in chickens which needs to be further investigated in APEC primed birds.

Dietary essential oils improves the growth performance, antioxidant properties and intestinal permeability by inhibiting bacterial proliferation and altering the gut microbiota of yellow-feather broilers

This experiment was conducted to investigate the antibacterial effects of essential oils (EO) in vitro and the influence of EO on growth performance, intestinal morphology and oxidation resistance and cecal microflora of yellow-feathered broilers. A total of 720 one-day-old male yellow feather broilers were randomly assigned into 4 treatments with 6 replicate cages of 30 broilers each. The groups were as follows: CON group (basal diet), EO200 group (basal diet + 200 mg/kg EO), EO400 group (basal diet + 400 mg/kg EO), and EO600 group (basal diet + 600 mg/kg EO). The experiment lasted for 48 d. Results showed that the growth and biofilm formation of avian pathogenic E. coli O78 and Salmonella pullorum were limited by adding EO to the diet (P < 0.05). Besides, birds fed with EO had greater (P < 0.05) average daily feed intake (ADFI), average daily gain (ADG), and body weight (BW) during d 1 to 21, 22 to 42, and 1 to 48 and lower (P < 0.05) feed: gain (F:G) than those fed with basal diet during d 22 to 42 and 1 to 48. Moreover, the activity of antioxidant enzyme and the intestinal permeability were improved in the EO400 and EO600 groups rather than the CON group on d 21 (P < 0.05). There were significant differences in cecal microbial composition and enrichment of metabolic pathways of birds among all groups by 16S-based sequencing. In summary, some dose of EO improved bacteriostatic ability, antioxidant ability, and intestinal health of broilers which contributed to the growth performance improvement of yellow-feathered broilers, which can be a promising antibiotic alternative for improving poultry production.

Evaluation of Novel Quorum Sensing Inhibitors Targeting Auto-Inducer 2 (AI-2) for the Control of Avian Pathogenic Escherichia coli Infections in Chickens

Avian pathogenic Escherichia coli (APEC) associated with colibacillosis results in high morbidity and mortality, and severe economic losses to the poultry industry. APEC is a zoonotic pathogen and can infect humans through contaminated poultry products. Vaccination and antibiotic treatment are currently used to control APEC infections; however, the limited effect of vaccines and the emergence of antibiotic-resistant strains have necessitated the development of novel therapeutics. Here, we evaluated seven quorum sensing inhibitors (QSI) identified in our previous study, in APEC-infected chickens. QSIs were administered orally (~92 to 120 μg/bird) and chickens were challenged subcutaneously with APEC. Among them, QSI-5 conferred the best protection (100% reduction in mortality, 82% to 93% reduction in lesions [airsacculitis, perihepatitis, lung congestion, pericarditis] severity, and 5.2 to 6.1 logs reduction in APEC load). QSI-5 was further tested in chickens raised on built-up floor litter using an optimized dose (1 mg/L) in drinking water. QSI-5 reduced the mortality (88.4%), lesion severity (72.2%), and APEC load (2.8 logs) in chickens, which was better than the reduction observed with currently used antibiotic sulfadimethoxine (SDM; mortality 35.9%; lesion severity up to 36.9%; and APEC load up to 2.4 logs). QSI-5 was detected in chicken's blood after 0.5 h with no residues in muscle, liver, and kidney. QSI-5 increased the body weight gain with no effect on the feed conversion ratio and cecal microbiota of the chickens. Metabolomic studies revealed reduced levels of 5'-methylthioadenosine in QSI-5-treated chicken serum. In conclusion, QSI-5 displayed promising effects in chickens and thus, represents a novel anti-APEC therapeutic. IMPORTANCE Avian pathogenic Escherichia coli (APEC), a subgroup of ExPEC, is a zoonotic pathogen with public health importance. Quorum sensing is a mechanism that regulates virulence, biofilm formation, and pathogenesis in bacteria. Here, we identified a novel quorum sensing autoinducer-2 inhibitor, QSI-5, which showed higher anti-APEC efficacy in chickens compared to the currently used antibiotic, sulfadimethoxine at a much lower dose (up to 4,500 times). QSI-5 is readily absorbed with no residues in the tissues. QSI-5 also increased the chicken's body weight gain and did not impact the cecal microbiota composition. Overall, QSI-5 represents a promising lead compound for developing novel anti-virulence therapies with significant implications for treating APEC infections in chickens as well as other ExPEC associated infections in humans. Further identification of its target(s) and understanding the mechanism of action of QSI-5 in APEC will add to the future novel drug development efforts that can overcome the antimicrobial resistance problem.

Isolation, Molecular Characterization, and Antibiotic Resistance of Avian Pathogenic Escherichia coli in Eastern China

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avians, resulting in considerable losses in the poultry industry. APEC showed zoonotic potential initially related to the fact that APEC serves as the reservoir of virulence genes and antibiotic resistance genes for other E. coli. Thus, we determine the serotypes, phylogenetic groups, virulence genes distribution, and antibiotic resistance profiles of APEC isolates in eastern China. A total of 230 APEC were isolated from diseased chicken and duck with typical colibacillosis symptoms. Serotyping identified that O78 (44.78%) was the predominant serotype. The majority of APEC isolates were classified into B2 (29.57%), A (26.96%), D (20.00%), and B1 (18.26%), respectively. Among the 15 virulence genes, a high prevalence of ibeB (99.57%), fimC (91.74%), mat (91.30%), ompA (83.04%), and iss (80.43%) genes was observed. Except for low resistance rates for imipenem (1.7%) and polymyxin B (0.4%), most of the APEC isolates were resistant to erythromycin (98.7%), enrofloxacin (96.1%), tetracycline (95.2%), doxycycline (93.9%), lincomycin (90.0%), and streptomycin (90.0%). Moreover, all APEC exhibit multi-drug resistance. This study indicated that APEC isolates harbor a variety of virulence genes and showed multi-antibiotic resistance profiles, providing proof for understanding the epidemiological background and zoonotic potential of APEC in poultry farms.

A Siderophore-Encoding Plasmid Encodes High-Level Virulence in Escherichia coli

A plasmid that harbored the virulence factors highly like those of the virulence plasmid commonly found in clinical hypervirulent Klebsiella pneumoniae strains was detected in a foodborne Escherichia coli strain EC1108 and designated p1108-IncFIB. This virulent-like plasmid was found to be common in E. coli from various sources. To understand the contribution of this plasmid to the virulence of E. coli, plasmid p1108-IncFIB in strain EC1108 was first cured to generate strain EC1108-PC. The virulence plasmid p15WZ-82_Vir in Klebsiella pneumoniae strain 15WZ-82 was then transmitted to EC1108-PC to produce the transconjugant, EC1108-PC-TC to assess the contribution of this virulence plasmid to the virulence level of E. coli. During the process of conjugation, p15WZ-82_Vir was found to be evolved into p15WZ-82_int, which underwent homologous recombination with a plasmid encoding a carbapenemase gene, bla_NDM-1, p1108-NDM, in EC1108-PC. Comparison between the level of virulence in the EC1108, EC1108-PC-TC, and EC1108-PC through serum and macrophage resistance assay, as well as animal experiments, confirmed that plasmid p1108-IncFIB encoded a high level of virulence in E. coli, yet the fusion plasmid derived from p15WZ-82_Vir did not encode virulence but instead imposed a high fitness cost in the E. coli strain EC1108-PC-TC. These findings indicate that E. coli strains carrying the virulence plasmid p1108-IncFIB in multidrug-resistant (MDR) strains may also impose serious public health threats like that of hypervirulent Klebsiella pneumoniae strains harboring the p15WZ-82_Vir plasmid.

IMPORTANCE Acquisition of pLVPK-like virulence plasmid by Klebsiella pneumoniae converts it to hypervirulent K. pneumoniae (HvKP), which has become one of the most important clinical bacterial pathogens. The potential of transmission of this virulence plasmid and its contribution to the virulence of other Enterobacteriaceae, such as E. coli, are not clear yet. In this study, we showed that pLVPK-like virulence plasmid exhibited fitness costs and did not contribute to the virulence in E. coli. However, we identified a novel virulence plasmid, p1108-IncFIB, that encodes similar siderophore genes as those of pLVPK from a foodborne E. coli strain and showed that p1108-IncFIB encoded a high level of virulence in E. coli. BLAST of E. coli genomes from GenBank showed that these siderophore genes were widespread in clinical E. coli strains. Further studies are warranted to understand the impact of this plasmid in the control of clinical infections caused by E. coli.

Transcriptional Regulation of RIP2 Gene by NFIB Is Associated with Cellular Immune and Inflammatory Response to APEC Infection

Avian pathogenic E. coli (APEC) can cause localized or systemic infection, resulting in large economic losses per year, and impact health of humans. Previous studies showed that RIP2 (receptor interacting serine/threonine kinase 2) and its signaling pathway played an important role in immune response against APEC infection. In this study, chicken HD11 cells were used as an in vitro model to investigate the function of chicken RIP2 and the transcription factor binding to the RIP2 core promoter region via gene overexpression, RNA interference, RT-qPCR, Western blotting, dual luciferase reporter assay, CHIP-PCR, CCK-8, and flow cytometry assay following APEC stimulation. Results showed that APEC stimulation promoted RIP2 expression and cells apoptosis, and inhibited cells viability. Knockdown of RIP2 significantly improved cell viability and suppressed the apoptosis of APEC-stimulated cells. Transcription factor NFIB (Nuclear factor I B) and GATA1 (globin transcription factor 1) binding site was identified in the core promoter region of RIP2 from −2300 bp to −1839 bp. However, only NFIB was confirmed to be bound to the core promoter of RIP2. Overexpression of NFIB exacerbated cell injuries with significant reduction in cell viability and increased cell apoptosis and inflammatory cytokines levels, whereas opposite results were observed in NFIB inhibition treatment group. Moreover, RIP2 was up-regulated by NFIB overexpression, and RIP2 silence mitigated the effect of NFIB overexpression in cell apoptosis, inflammation, and activation of NFκB signaling pathways. This study demonstrated that NFIB overexpression accelerated APEC-induced apoptosis and inflammation via up-regulation of RIP2 mediated downstream pathways in chicken HD11 cells.

Investigation of Serotype Prevalence of Escherichia coli Strains Isolated from Layer Poultry in Greece and Interactions with Other Infectious Agents

Colibacillosis is the most common bacterial disease in poultry and it is caused by avian pathogenic Escherichia coli (APEC), which is assigned to various O-serogroups. Previous studies have shown that APEC strains are more often related to certain O-serogroups such asO78, O2 and O1. E. coli has been reported to act either as a primary or secondary agent in complicating other infections. The aim of this study was to investigate the occurrence of and characterize the O-serogroups of E. coli strains isolated from commercial layer and layer breeder flocks showing macroscopic lesions of colibacillosis and increased or normal mortality in Greece. Furthermore, we attempted to assess the interaction between infectious agents such as Mycoplasma gallisepticum (MG), Mycoplasma synoviae (MS), infectious bronchitis (IBV) and infectious laryngotracheitis (ILT) with E. coli infections in layer flocks with increased mortality. Our study revealed that in addition to the common serogroups (O78, O2), many other, and less common serogroups were identified, including O111. The O78, O111 and O2 serogroups were frequently detected in flocks with lesions of colibacillosis and increased mortality whereas O2, O88 and O8 were reported more commonly in birds with colibacillosis lesions but normal mortality rates. These data provide important information for colibacillosis monitoring and define preventative measures, especially by using effective vaccination programs because E. coli vaccines are reported to mainly offer homologous protection. Finally, concerning the association of the four tested infectious agents with E. coli mortality, our study did not reveal a statistically significant effect of the above infectious agents tested with E. coli infection mortality.

Bacteriophage therapy as an alternative biocontrol against emerging multidrug resistant E. coli in broilers

Avian pathogenic Escherichia coli (APEC) is considered a severe issue to both poultry business and health of the general public. In that context, 50 samples from 250 diseased broiler chickens in 10 chicken farms were employed to Escherichia coli isolation. Microbiological techniques were employed to detect isolates of E. coli from 250 diseased broiler chickens which were examined by antimicrobial susceptibility profiles against 11 antimicrobial agents using disc diffusion technique as well as their biofilm forming capacity were detected. In addition to, study the isolation and purification of phages based on spot technique to verify that lytic phages are present in E. coli isolates and plaque assay for titration of bacteriophages. In the present research, we also looked at the ability of bacteriophages to inhibit and dissolve previously formed biofilms by E. coli O78 isolate. Moreover, experimental testing of E. coli O78 bacteriophages for colibacillosis prevention and control in one day old broiler chicks were done. The obtained results showed that twenty-six E. coli isolates out of 50 examined samples were isolated (10.4%). The most prevalent serotypes were O78, O121:H7, O146:H2, O124, O113:H4, O112:H2, O1:H7, O55:H7, O2:H6, O91:H21, O26:H11. Antibiogram results demonstrated the resistance of E. coli isolates with high percentage 100% were against, Ampicillin, Amoxicillin and Tetracycline. Biofilm quantification analysis showed that 24/26 (92.3%) isolates were considered biofilm producer isolates. The characterization and the lytic activity of bacteriophage were performed based on Transmission electron microscopy and showed the greatest lytic activity against the evaluated host strains with effective activity at concentration of 10⁷ at 24 h and strong significant reduction of the established E. coli O 78 biofilm within 12 h. The result of experimental infection showed that the performance indicators of phage in treated and challenged group showed high significant increase in body weight, weight gain and improved FCR than infected –antibiotic treated and infected bacteriophage and antibiotic treated. Total viable cell counts of E. coli in the lungs of birds revealed that there is highly significant difference between the six groups count results. We concluded that phage therapy found to be an attractive option to prevent and control multidrug resistant colibacillosis in broilers.

Challenges in Veterinary Vaccine Development

Animals provide food and clothing in addition to other value-added products. Changes in diet and lifestyle have increased the consumption and the use of animal products. Infectious diseases in animals are a major threat to global animal health and its welfare; their effective control is crucial for agronomic health, for safeguarding food security and also alleviating rural poverty. Development of vaccines has led to increased production of healthy poultry, livestock, and fish. Animal production increases have alleviated food insecurity. In addition, development of effective vaccines has led to healthier companion animals. However, challenges remain including climate change that has led to enhancement in vectors and pathogens that may lead to emergent diseases in animals. Preventing transmission of emerging infectious diseases at the animal-human interface is critically important for protecting the world population from epizootics and pandemics. Hence, there is a need to develop new vaccines to prevent diseases in animals. This review describes the broad challenges to be considered in the development of vaccines for animals.

Combining pangenome analysis to identify potential cross-protective antigens against avian pathogenic Escherichia coli

AbstractAvian pathogenic Escherichia coli (APEC) is the bacterial pathogen of poultry colibacillosis, which causes significant economic losses to the poultry industry. The lack of an effective vaccine against multiple serotypes and the emergence of multi-resistant isolates have made the control of avian colibacillosis troublesome. To identify conserved potential vaccine candidates, 58 genomes of APEC were obtained (54 sequenced by our laboratory and 4 downloaded from NCBI). A reverse vaccinology (RV) method based on the pangenome - called Pan-RV analysis - was performed in APEC-protective protein mining for the first time. Finally, four proteins were selected, and their immunoreactivity with anti-O1, O2, and O78 serum was verified by western blotting. Our in silico method of analysis will pave the way for rapid screening of vaccine candidates and will lay the foundation for the development of a highly effective subunit vaccine controlling APEC infection.

Novel Small Molecule Growth Inhibitor Affecting Bacterial Outer Membrane Reduces Extraintestinal Pathogenic Escherichia coli (ExPEC) Infection in Avian Model

Avian pathogenic Escherichia coli (APEC), a subgroup of extraintestinal pathogenic E. coli (ExPEC), causes colibacillosis in chickens and is reportedly implicated in urinary tract infections and meningitis in humans. A major limitation for the current ExPEC antibiotic therapy is the development of resistance, and antibacterial drugs that can circumvent this problem are critically needed. Here, we evaluated eight novel membrane-affecting anti-APEC small molecule growth inhibitors (GIs), identified in our previous study, against APEC infection in chickens. Among the GIs tested, GI-7 (the most effective), when administered orally (1 mg/kg of body weight), reduced the mortality (41.7%), severity of lesions (62.9%), and APEC load (2.6 log) in chickens. Furthermore, GI-7 administration at an optimized dose (60 mg/liter) in drinking water also reduced the mortality (14.7%), severity of lesions (29.5%), and APEC load (2.2 log) in chickens. The abundances of Lactobacillus and oleate were increased in the cecum and serum, respectively, of GI-7-treated chickens. Pharmacokinetic analysis revealed that GI-7 was readily absorbed with minimal accumulation in the tissues. Earlier, we showed that GI-7 induced membrane blebbing and increased membrane permeability in APEC, suggesting an effect on the APEC membrane. Consistent with this finding, the expression of genes essential for maintaining outer membrane (OM) integrity was downregulated in GI-7-treated APEC. Furthermore, decreased levels of lipopolysaccharide (LPS) transport (Lpt) proteins and LPS were observed in GI-7-treated APEC. However, the mechanism of action of GI-7 currently remains unknown and needs further investigation. Our studies suggest that GI-7 represents a promising novel lead compound that can be developed to treat APEC infection in chickens and related human ExPEC infections. IMPORTANCE APEC is a subgroup of ExPEC, and genetic similarities of APEC with human ExPECs, including uropathogenic E. coli (UPEC) and neonatal meningitis E. coli (NMEC), have been reported. Our study identified a novel small molecule growth inhibitor, GI-7, effective in reducing APEC infection in chickens with an efficacy similar to that of the currently used antibiotic sulfadimethoxine, notably with an 8-times-lower dose. GI-7 affects the OM integrity and decreases the Lpt protein and LPS levels in APEC, an antibacterial mechanism that can overcome the antibiotic resistance problem. Overall, GI-7 represents a promising lead molecule/scaffold for the development of novel antibacterial therapies that could have profound implications for treating APEC infections in chickens, as well as human infections caused by ExPECs and other related Gram-negative bacteria. Further elucidation of the mechanism of action of GI-7 and identification of its target(s) in APEC will benefit future novel antibacterial development efforts.

Protective Potential of an Autogenous Vaccine in an Aerogenous Model of Escherichia coli Infection in Broiler Breeders

In poultry, Escherichia coli is a common cause of high-cost infections. Consequently, autogenous vaccines are often used despite limited and conflicting evidence on their effectiveness have been presented. The present study aimed to investigate the efficacy of a commonly used autogenous vaccine, previously deemed ineffective, in an aerosol model of colibacillosis. Methods: Broiler breeders (n = 47) were randomly allocated to one of four groups (vaccinated and unvaccinated birds receiving an autogenous vaccine or sterile saline intramuscularly) and challenged with either aerosolised E. coli or vehicle at 29 weeks of age. Two days following inoculation, the birds were euthanised, thoroughly necropsied, and samples for bacteriology and histopathology were collected. Results: Vaccinated birds had a significantly lower bacteriology score compared to the unvaccinated group challenged with E. coli (p < 0.01) and a lower overall air sac lesion score (p < 0.05). Overall lung and spleen lesion scores only differed significantly between the unvaccinated E. coli challenged group compared to the vehicle inoculated groups. The overall gross pathology score was 2.8 and 1.95 in the unvaccinated and vaccinated E. coli challenge groups, respectively, whereas the vaccinated vehicle group had a score of 0.9 and the unvaccinated vehicle group a score of 1. Conclusions: A protective effect of an autogenous vaccine was found utilising an aerogenous model of colibacillosis through multiple methods of evaluation. The findings encourage the continued use of autogenous vaccines and underlines the necessity of discriminative experimental models with high predictive validity when evaluating vaccine interventions.

Avian Pathogenic Escherichia coli (APEC): An Overview of Virulence and Pathogenesis Factors, Zoonotic Potential, and Control Strategies

Avian pathogenic Escherichia coli (APEC) causes colibacillosis in avian species, and recent reports have suggested APEC as a potential foodborne zoonotic pathogen. Herein, we discuss the virulence and pathogenesis factors of APEC, review the zoonotic potential, provide the current status of antibiotic resistance and progress in vaccine development, and summarize the alternative control measures being investigated. In addition to the known virulence factors, several other factors including quorum sensing system, secretion systems, two-component systems, transcriptional regulators, and genes associated with metabolism also contribute to APEC pathogenesis. The clear understanding of these factors will help in developing new effective treatments. The APEC isolates (particularly belonging to ST95 and ST131 or O1, O2, and O18) have genetic similarities and commonalities in virulence genes with human uropathogenic E. coli (UPEC) and neonatal meningitis E. coli (NMEC) and abilities to cause urinary tract infections and meningitis in humans. Therefore, the zoonotic potential of APEC cannot be undervalued. APEC resistance to almost all classes of antibiotics, including carbapenems, has been already reported. There is a need for an effective APEC vaccine that can provide protection against diverse APEC serotypes. Alternative therapies, especially the virulence inhibitors, can provide a novel solution with less likelihood of developing resistance.

Ways to minimize bacterial infections, with special reference to Escherichia coli, to cope with the first-week mortality in chicks: an updated overview

On the commercial level, the poultry industry strives to find new techniques to combat bird's infection. During the first week, mortality rate increases in birds because of several bacterial infections of about ten bacterial species, especially colisepticemia. This affects the flock production, uniformity, and suitability for slaughter because of chronic infections. Escherichia coli (E. coli) causes various disease syndromes in poultry, including yolk sac infection (omphalitis), respiratory tract infection, and septicemia. The E. coli infections in the neonatal poultry are being characterized by septicemia. The acute septicemia may cause death, while the subacute form could be characterized through pericarditis, airsacculitis, and perihepatitis. Many E. coli isolates are commonly isolated from commercial broiler chickens as serogroups O₁, O₂, and O₇₈. Although prophylactic antibiotics were used to control mortality associated with bacterial infections of neonatal poultry in the past, the commercial poultry industry is searching for alternatives. This is because of the consumer's demand for reduced antibiotic-resistant bacteria. Despite the vast and rapid development in vaccine technologies against common chicken infectious diseases, no antibiotic alternatives are commercially available to prevent bacterial infections of neonatal chicks. Recent research confirmed the utility of probiotics to improve the health of neonatal poultry. However, probiotics were not efficacious to minimize death and clinical signs associated with neonatal chicks' bacterial infections. This review focuses on the causes of the increased mortality in broiler chicks during the first week of age and the methods used to minimize death.

Genetic resistance to avian pathogenic Escherichia coli (APEC): current status and opportunities

Infections with avian pathogenic Escherichia coli (APEC) can be extremely detrimental to poultry health and production. Investigating host genetic variation could identify the biological mechanisms that control resistance to this pathogen and allow selection for improved resistance in experimental and commercial poultry populations. In this review, the current knowledge of how host genetics contributes to APEC resistance and future opportunities that would benefit the understanding or application of genetic resistance are discussed. Phenotypes, such as antibody responses, lesion scores, and mortality, revealed that genetic background impacts APEC resistance and interacts with other factors including the environment and challenge conditions. Experiments have used divergent selection for APEC-specific antibody levels to facilitate genetic studies, estimated heritabilities in relevant traits, detected quantitative trait loci using microsatellites, and made associations with sequence variation in the major histocompatibility complex, which collectively suggest that improving APEC resistance through selection is feasible, although genetic control is partial, complex, and highly polygenic. Additionally, functional genomics techniques have identified antimicrobial responses, toll-like receptor and cytokine signalling, and the cell cycle as central pathways in the host response to APEC challenge. Opportunities for future research are discussed, including the expansion of existing lines of research and the application of new technologies that are relevant to the study of host genetics and APEC. This review closes with prospective strategies for improvement of host genetic resistance to APEC.

Regulated delayed attenuation improves vaccine efficacy in preventing infection from avian pathogenic Escherichia coli O78 and Salmonella typhimurium

Avian pathogenic Escherichia coli (APEC) O₇₈ and Salmonella typhimurium (S. Typhimurium) are two leading bacterial pathogens that cause significant economic loss in the poultry industry. O-antigen is an important immunogen of these two bacteria to induce host protective immune responses during infection. To develop a bivalent vaccine against APEC O₇₈ and S. Typhimurium, the attenuated Salmonella ST01 (Δasd ΔrfbP Δcrp) was genetically constructed to deliver APEC O₇₈ O-antigen polysaccharide (OPS), which stably expresses OPS with asd⁺ balanced-lethal system in vitro and in vivo. After oral immunization, the recombinant attenuated Salmonella vaccine (RASV) strain ST01 (pSS26-O₇₈) provided insufficient protection against the APEC O₇₈ challenge. Therefore, the regulated delayed attenuation strain ST02 (Δasd ΔrfbP ΔPcrp::TTaraC P_BADcrp) was further constructed by regulating cyclic AMP receptor protein (crp) with araC P_BAD cassette to better present the heterologous O-antigen to the host immune system. The innovative recombinant strain ST02 (pSS26-O₇₈) stimulated robust antibody responses against APEC O₇₈ and S. Typhimurium OPS, with serum titers over 1:800 for both IgG and IgA, thereby providing the complement-mediated bactericidal activity and stronger protection against APEC O₇₈ and S. Typhimurium infection. Collectively, this study demonstrates a biologically-conjugated polysaccharide vaccine candidate that can enhance homologous protection against APEC O₇₈ and S. Typhimurium.

Synthesis of a Pentasaccharide Repeating Unit of Lipopolysaccharide Derived from Virulent E. coli O1 and Identification of a Glycotope Candidate of Avian Pathogenic E. coli O1

Avian pathogenic Escherichia coli (APEC) is a common bacterial pathogen infecting chickens, resulting in economic losses to the poultry industry worldwide. In particular, APEC O1, one of the most common serotypes of APEC, is considered problematic due to its zoonotic potential. Therefore, many attempts have been made to develop an effective vaccine against APEC O1. In fact, the lipopolysaccharide (LPS) O-antigen of APEC O1 has been shown to be a potent antigen for inducing specific protective immune responses. However, the detailed structure of the O-antigen of APEC O1 is not clear. The present study demonstrates the first synthesis of a pentasaccharide repeating unit of LPS derived from virulent E. coli O1 and its conjugate with BSA. ELISA tests using the semi-synthetic glycoconjugate and the APEC O1 immune chicken serum revealed that the pentasaccharide is a glycotope candidate of APEC O1, with great potential as an antigen for vaccine development.

Design, development, and evaluation of the efficacy of a nucleic acid-free version of a bacterial ghost candidate vaccine against avian pathogenic E. coli (APEC) O78:K80 serotype

One of the major bacterial infectious diseases in the poultry industry is avian pathogenic Escherichia coli (APEC), which causes colibacillosis in chickens. To develop a novel nucleic acid-free bacterial ghost (BG) vaccine against the O78:K80 serotype of APEC, in this study we constructed a plasmid that harbored E-lysis and S nuclease (SNUC). Following the expression, the O78:K80 bacteria lost all of their cytoplasmic content and nucleic acids by enzymatic digestion. The functionality of these two proteins in the production procedure of bacterial ghosts was confirmed by monitoring the number of colonies, scanning electron microscopy imaging, gel electrophoresis of genomic DNA, and qPCR on the plasmid content of bacterial ghosts. The protective efficacy of the ghost vaccine generated from O78:K80 serotype of APEC was tested in chickens by injection and inhalation routes and compared with that in chickens that received the injection of a killed vaccine. The O78:K80 BG vaccine candidate, used as injection and inhalation, in comparison with the killed vaccine, triggered higher proinflammatory cytokine expression including IL-6, IL-1β, and TNFSF15; a higher level of antibody-dependent humoral (IgY and IgA) and cellular immune responses (IFNγ and lymphocyte proliferation); and lower lesion scores. According to the results of this study, we suggest that the bacterial ghost technology has the potential to be applied for the development of novel vaccines against avian colibacillosis. This technology provides an effective and reliable approach to make multivalent vaccines for more prevalent APEC strains involved in the establishment of this infectious disease in the poultry industry.