Expression of Escherichia coli antigens in Salmonella typhimurium as a vaccine to prevent airsacculitis in chickens

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.

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.

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.

Characterization of Spleen Transcriptome and Immunity Against Avian Colibacillosis After Immunization With Recombinant Attenuated Salmonella Vaccine Strains

Avian pathogenic Escherichia coli (APEC) causes extraintestinal infections in poultry. Vaccines targeting APEC in chickens have been partially successful, but many lack heterologous protection. Recombinant attenuated Salmonella vaccine (RASV) strains can induce broad immunity against Salmonella and be modified to deliver E. coli antigens. Along with vaccine characteristics, understanding the host response is crucial for developing improved vaccines. The objectives of this study were to evaluate host responses to vaccination with an RASV producing E. coli common pilus (ECP) and assess protection against APEC infection in chickens. Four-day-old White Leghorn chickens were unvaccinated or orally vaccinated and boosted 2 weeks later with RASV χ8025(pYA3337), RASV χ8025(pYA4428) carrying ecp operon genes, or a combination of χ8025(pYA3337) and χ8025(pYA4428) (Combo). To assess host responses, serum IgY and intestinal IgA antibody titers were measured, and spleen samples (n = 4/group) were collected from unvaccinated and Combo vaccinated 4-week-old chickens for RNA-seq. Vaccine protection potential against Salmonella and APEC was evaluated in vitro using bacterial inhibition assays. Five-week-old chickens were challenged via air sac with either an APEC O2 or O78 strain. E. coli was enumerated from internal organs, and gross colibacillosis lesions were scored at necropsy. RASV immunized chickens elicited anti-E. coli antibodies. The spleen transcriptome revealed that 93% (89/96) of differentially expressed genes (DEG) were more highly expressed in Combo vaccinated compared to unvaccinated chickens, with signal as the most significantly impacted category. RNA-seq analysis also revealed altered cellular and metabolic processes, response to stimulus after vaccination, and immune system processes. Six DEG including genes linked to transcription regulation, actin cytoskeleton, and signaling were highly positively correlated with antibody levels. Samples from RASV immunized chickens showed protection potential against Salmonella strains using in vitro assays, but a variable response was found for APEC strains. After APEC challenges, significant differences were not detected for bacterial loads or gross lesions scores, but χ8025(pYA3337) immunized and χ8025(pYA4428) immunized chickens had significantly fewer number of APEC-O2-positive samples than unvaccinated chickens. This study shows that RASVs can prime the immune system for APEC infection, and is a first step toward developing improved therapeutics for APEC infections in chickens.

Plague Vaccines: Status and Future

Three major plague pandemics caused by the gram-negative bacterium Yersinia pestis have killed nearly 200 million people in human history. Due to its extreme virulence and the ease of its transmission, Y. pestis has been used purposefully for biowarfare in the past. Currently, plague epidemics are still breaking out sporadically in most of parts of the world, including the United States. Approximately 2000 cases of plague are reported each year to the World Health Organization. However, the potential use of the bacteria in modern times as an agent of bioterrorism and the emergence of a Y. pestis strain resistant to eight antibiotics bring out severe public health concerns. Therefore, prophylactic vaccination against this disease holds the brightest prospect for its long-term prevention. Here, we summarize the progress of the current vaccine development for counteracting plague.

An experimental infection model for Escherichia coli egg peritonitis in layer chickens

The present study describes an experimental infection model for avian pathogenic Escherichia coli (APEC)-induced egg peritonitis in layer chickens. First, a pilot study which consisted of two separate experiments was carried out to compare two routes of inoculations of APEC to induce peritonitis and to examine if the presence of egg yolk in the peritoneum would facilitate APEC-induced peritonitis. This study showed that the presence of egg yolk in the peritoneum facilitated the development of egg peritonitis when the APEC was inoculated via the intra-uterine (IU) route. Based on the results of the pilot study, 56-wk-old white leghorn hens were divided into two groups of five chickens, Group G (inoculated with E. coli APECO78 strain) and Group H (control). Both groups were inoculated with 2-3 ml of egg yolk via the intraperitoneal route (IP). Subsequently, hens in Group H were inoculated with only egg yolk whereas the hens in Group G were inoculated with 1 x 10(9) colony-forming units of APECO78 bacteria via the IU route. Parameters such as mortality, clinical signs (anorexia, depression, and egg production efficiency), gross lesion scores, bacterial loads in internal organs, and histopathology of ovary and oviduct were assessed to evaluate the success of the infection model. Group G showed 40% acute mortality, severe depression, and anorexia with markedly reduced egg production and developed peritonitis-associated lesions such as accumulation of yellowish caseous fluid in the peritoneum, salpingitis, and oophoritis. Histopathologically, ovarian and oviduct tissues from group G exhibited severe inflammatory changes such as infiltration of mononuclear cells and edema. Group G also showed significant bacterial loads in the peritoneum, ovary, and oviduct. Interestingly, deceased birds from group G had also developed mild perihepatitis and pericarditis with heavy bacterial loads in the internal organs. On the other hand, group H birds did not exhibit any of the clinical signs and remained healthy until the end of the experiment. To summarize, our results demonstrate that IP administration of egg yolk followed by IU inoculation of APECO78 induced peritonitis in laying hens. Experimental infection models are often required to understand the mechanisms of disease pathogenesis. Therefore, the present infection model will aid in the studies of pathogenesis of layer peritonitis caused by APEC and in evaluating vaccine candidates to control the disease.

Construction of an attenuated Salmonella delivery system harboring genes encoding various virulence factors of avian pathogenic Escherichia coli and its potential as a candidate vaccine for chicken colibacillosis

An attenuated Salmonella (deltalon, deltacpxR, and deltaasdA16) delivery system containing the genes encoding P-fimbriae (papa and papG), aerobactin receptor (iutA), and CS31A surface antigen (clpG) of avian pathogenic Escherichia coli (APEC) was constructed, and its potential as a vaccine candidate against APEC infection in chickens was evaluated. The birds were divided into three groups designated group A (nonvaccinated control), group B (given a single immunization), and group C (administered prime and boost immunizations). Prime and booster vaccinations with the constructions were administered to 1-day-old and 14-day-old birds, respectively. Immune responses were measured postimmunization, and the birds were challenged via an intra-air sac route with a virulent APEC strain at the second, third, and fourth weeks of age. Group B birds were partially protected against the challenge and showed increased levels of plasma immunoglobulin (Ig)G, mucosal IgA antibodies, and lymphocyte proliferation. Group C birds showed greater protection against the challenge, with significantly stronger immune responses compared with the birds in the other groups. Overall, our data suggest that the Salmonella delivery system with recombinant constructs is capable of inducing robust immune responses and induces effective protection against colibacillosis caused by APEC.

Mucosal vaccination with a codon-optimized hemagglutinin gene expressed by attenuated Salmonella elicits a protective immune response in chickens against highly pathogenic avian influenza

The purpose of this study was to evaluate clinical protection from challenge conferred by two attenuated Salmonella enteria serovar typhimurium vaccine strains expressing the hemagglutinin (HA1) gene from a highly pathogenic avian influenza (HPAI) H5N1 (A/whooper swan/Mongolia/3/2005), under control of the anaerobically inducible nir15 promoter. Two-week-old White Leghorn chickens were immunized by oral gavage with one milliliter doses of >109 Salmonella colony-forming units once weekly for 4 weeks prior to challenge. Expression of recombinant protein was confirmed via Western blot. Serum and mucosal gavage samples were collected prior to, and following immunization and antibodies against avian influenza HA were confirmed by Western blot and hemagglutination-inhibition (HI) assay. Chickens were challenged with homologous (A/whooper swan/Mongolia/3/2005), or heterologous (A/Chicken/Queretaro/14588-19/95) HPAI virus strains. Chickens immunized with attenuated Salmonella strains containing plasmid expression vector (pTETnir15HA) demonstrated a statistically significant increase in survival compared to control groups. Results provide evidence of effectiveness of attenuated Salmonella strains for delivery of recombinant avian influenza HA antigens and induction of mucosal and systemic immune responses protective against lethal challenge with HPAI.

A live oral recombinant Salmonella enterica serovar typhimurium vaccine expressing Clostridium perfringens antigens confers protection against necrotic enteritis in broiler chickens

Necrotic enteritis (NE) in broiler chickens is caused by Clostridium perfringens, and there is currently no effective vaccine for NE. We previously showed that in broiler chickens protection against NE can be achieved through intramuscular immunization with alpha toxin (AT) and hypothetical protein (HP), and we subsequently identified B-cell epitopes in HP. In the present study, we identified B-cell epitopes in AT recognized by chickens immune to NE. The gene fragments encoding immunodominant epitopes of AT as well as those of HP were codon optimized for Salmonella and cloned into pYA3493, and the resultant plasmid constructs were introduced into an attenuated Salmonella enterica serovar Typhimurium chi9352 vaccine vehicle. The expression of these Clostridium perfringens proteins, alpha toxoid (ATd) and truncated HP (HPt), was confirmed by immunoblotting. The protection of broiler chickens against experimentally induced NE was assessed at both the moderate and the severe levels of challenge. Birds immunized orally with Salmonella expressing ATd were significantly protected against moderate NE, and there was a nonsignificant trend for protection against severe challenge, whereas HPt-immunized birds were significantly protected against both severities of challenge. Immunized birds developed serum IgY and mucosal IgA and IgY antibody responses against Clostridium and Salmonella antigens. In conclusion, this study identified, for the first time, the B-cell epitopes in AT from an NE isolate recognized by chickens and showed the partial protective ability of codon-optimized ATd and HPt against NE in broiler chickens when they were delivered orally by using a Salmonella vaccine vehicle.

Identification of minimal predictors of avian pathogenic Escherichia coli virulence for use as a rapid diagnostic tool

To identify traits that predict avian pathogenic Escherichia coli (APEC) virulence, 124 avian E. coli isolates of known pathogenicity and serogroup were subjected to virulence genotyping and phylogenetic typing. The results were analyzed by multiple-correspondence analysis. From this analysis, five genes carried by plasmids were identified as being the most significantly associated with highly pathogenic APEC strains: iutA, hlyF, iss, iroN, and ompT. A multiplex PCR panel targeting these five genes was used to screen a collection of 994 avian E. coli isolates. APEC isolates were clearly distinguished from the avian fecal E. coli isolates by their possession of these genes, suggesting that this pentaplex panel has diagnostic applications and underscoring the close association between avian E. coli virulence and the possession of ColV plasmids. Also, the sharp demarcation between APEC isolates and avian fecal E. coli isolates in their plasmid-associated virulence gene content suggests that APEC isolates are well equipped for a pathogenic lifestyle, which is contrary to the widely held belief that most APEC isolates are opportunistic pathogens. Regardless, APEC isolates remain an important problem for poultry producers and a potential concern for public health professionals, as growing evidence suggests a possible role for APEC in human disease. Thus, the pentaplex panel described here may be useful in detecting APEC-like strains occurring in poultry production, along the food chain, and in human disease. This panel may be helpful toward clarifying potential roles of APEC in human disease, ascertaining the source of APEC in animal outbreaks, and identifying effective targets of avian colibacillosis control.

Immune Response to Recombinant Escherichia coli Iss Protein in Poultry

Colibacillosis accounts for significant losses to the poultry industry, and control efforts are hampered by limited understanding of the mechanisms used by avian pathogenic Escherichia coli (APEC) to cause disease. We have found that the presence of the increased serum survival gene (iss) is strongly associated with APEC but not with commensal E. coli, making iss, and the protein it encodes (Iss), candidate targets of colibacillosis control procedures. To assess the potential of Iss to elicit a protective response in chickens against APEC challenge, Iss fusion proteins were produced and administered subcutaneously to four groups of 2-wk-old specific-pathogen-free leghorn chickens. At 4 wk postimmunization, birds were challenged with APEC from serogroups 02 and 078 via intramuscular injection. At 2 wk postchallenge, birds were necropsied, and lesions consistent with colibacillosis were scored. Also, sera were collected from the birds pre- and postimmunization, and antibody titers to Iss were determined. Immunized birds produced a humoral response to Iss, and they had significantly lower lesion scores than the unimmunized control birds following challenge with both APEC strains. Birds that received the smallest amount of immunogen had the lowest lesion scores. Although further study will be needed to confirm the value of Iss as an immunoprotective antigen, these preliminary data suggest that Iss may have the potential to elicit significant protection in birds against heterologous E. coli challenge.