An attenuated mutant of avian pathogenic Escherichia coli serovar O78: a possible live vaccine strain for prevention of avian colibacillosis

The Isolation and Characterization of Bacteriophages Infecting Avian Pathogenic Escherichia coli O1, O2 and O78 Strains

Avian pathogenic Escherichia coli (APEC), such as O1, O2 and O78, are important serogroups relating to chicken health, being responsible for colibacillosis. In this study, we isolated and characterized bacteriophages (phages) from hen feces and human sewage in Alberta with the potential for controlling colibacillosis in laying hens. The lytic profile, host range, pH tolerance and morphology of seven APEC-infecting phages (ASO1A, ASO1B, ASO2A, ASO78A, ASO2B, AVIO78A and ASO78B) were assessed using a microplate phage virulence assay and transmission electron microscopy (TEM). The potential safety of phages at the genome level was predicted using AMRFinderPlus and the Virulence Factor Database. Finally, phage genera and genetic relatedness with other known phages from the NCBI GenBank database were inferred using the virus intergenomic distance calculator and single gene-based phylogenetic trees. The seven APEC-infecting phages preferentially lysed APEC strains in this study, with ECL21443 (O2) being the most susceptible to phages (n = 5). ASO78A had the broadest host range, lysing all tested strains (n = 5) except ECL20885 (O1). Phages were viable at a pH of 2.5 or 3.5-9.0 after 4 h of incubation. Based on TEM, phages were classed as myovirus, siphovirus and podovirus. No genes associated with virulence, antimicrobial resistance or lysogeny were detected in phage genomes. Comparative genomic analysis placed six of the seven phages in five genera: Felixounavirus (ASO1A and ASO1B), Phapecoctavirus (ASO2A), Tequatrovirus (ASO78A), Kayfunavirus (ASO2B) and Sashavirus (AVIO78A). Based on the nucleotide intergenomic similarity (<70%), phage ASO78B was not assigned a genus in the siphovirus and could represent a new genus in class Caudoviricetes. The tail fiber protein phylogeny revealed variations within APEC-infecting phages and closely related phages. Diverse APEC-infecting phages harbored in the environment demonstrate the potential to control colibacillosis in poultry.

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.

Amino Acid Substitution Ser83Ile in GyrA of DNA Gyrases Confers High-Level Quinolone Resistance to Nontyphoidal Salmonella Without Loss of Supercoiling Activity

Aims: Quinolone-resistant nontyphoidal Salmonella having serine replaced by isoleucine at the 83rd amino acid in GyrA (GyrA-Ser83Ile) has recently been found in Asian countries. In this study, we aimed to examine the direct effect of substitution Ser83Ile on DNA gyrase activity and/or resistance to quinolones. Materials and Methods: Using 50% of the maximal inhibitory concentrations (IC₅₀s) of quinolones, recombinant wild type (WT) and seven mutant DNA gyrases having amino acid substitutions, including Ser83Ile, were screened for enzymatic activity that causes supercoils in relaxed plasmid DNA and resistance to quinolones. Results: Little differences in supercoiling activity were observed between WT and mutant DNA gyrases. By contrast, the IC₅₀s of ciprofloxacin and norfloxacin against GyrA-Ser83Ile/GyrB-WT were 11.6 and 73.3 μg/mL, respectively, which were the highest used against the DNA gyrases examined in this study. Conclusion: Ser83Ile in GyrA was shown to confer high-level quinolone resistance to DNA gyrases of nontyphoidal Salmonella, with no loss of supercoiling activity. Salmonella strain carrying GyrA with Ser83Ile may emerge under a high-concentration pressure of quinolones and easily spread even with no selection bias by quinolones. Hence, avoiding the overuse of quinolones is needed to prevent the spread of Salmonella with Ser83Ile in GyrA.

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.

Immunization With Outer Membrane Vesicles Derived From Major Outer Membrane Protein-Deficient Salmonella Typhimurium Mutants for Cross Protection Against Salmonella Enteritidis and Avian Pathogenic Escherichia coli O78 Infection in Chickens

Colibacillosis is an economically important infectious disease in poultry, caused by avian pathogenic Escherichia coli (APEC). Salmonella enterica serovar Enteritidis (S. Enteritidis) is a major cause of food-borne diseases in human circulated through poultry-derived products, including meat and chicken eggs. Vaccine control is the mainstream approach for combating these infections, but it is difficult to create a vaccine for the broad-spectrum protection of poultry due to multiple serotypes of these pathogens. Our previous studies have shown that outer membrane vesicles (OMVs) derived from S. enterica serovar Typhimurium mutants with a remodeled outer membrane could induce cross-protection against heteroserotypic Salmonella infection. Therefore, in this study, we further evaluated the potential of broad-spectrum vaccines based on major outer membrane protein (OMP)-deficient OMVs, including ΔompA, ΔompC, and ΔompD, and determined the protection effectiveness of these candidate vaccines in murine and chicken infection models. The results showed that ΔompA led to an increase in the production of OMVs. Notably, ΔompAΔompCΔompD OMVs showed significantly better cross-protection against S. enterica serovar Choleraesuis, S. Enteritidis, APEC O78, and Shigella flexneri 2a than did other omp-deficient OMVs, with the exception of ΔompA OMVs. Subsequently, we verified the results in the chicken model, in which ΔompAΔompCΔompD OMVs elicited significant cross-protection against S. Enteritidis and APEC O78 infections. These findings further confirmed the feasibility of improving the immunogenicity of OMVs by remodeling the outer membrane and provide a new perspective for the development of broad-spectrum vaccines based on OMVs.

An Assessment of the Level of Protection Against Colibacillosis Conferred by Several Autogenous and/or Commercial Vaccination Programs in Conventional Pullets upon Experimental Challenge

The prevention of avian colibacillosis has historically been investigated through vaccination, with variable outcomes. Commercial live (attenuated) and inactivated vaccines are reported to have limited efficacy in the context of heterologous challenge. Autogenous vaccination, using field isolates, is widely used, but scarcely documented. Different vaccination programs, including a live commercial vaccine and/or an inactivated autogenous vaccine, were compared for three different avian pathogenic Escherichia coli (APEC) strain (serotypes O78, O18 and O111) challenges. On the pullet farm, four groups of conventional pullets received different vaccination protocols. Group A was kept unvaccinated (control group). Group B was vaccinated three times with a live commercial O78 E. coli vaccine (at one day old, 59 and 110 days of age). Group C was immunized twice (at 79 and 110 days) with a three-valence autogenous vaccine (O78, O18 and O111). Group D was vaccinated first with the commercial vaccine (at one day old and 59 days), then with the autogenous vaccine (110 days). Birds were transferred to the experimental facility at 121 days of age and were challenged 10 days later. In each group, 20 birds were challenged with one of the three APEC strains (O78, O18, O111); in total, 80 birds were challenged by the same strains (20 per group). The recorded outcomes were: mortality rate, macroscopic lesion score in target organs and the bacterial recovery of the challenge strain from bone marrow and pooled organs. When challenged with O78 or O111 strains, birds from groups C and D proved to be significantly better protected, in terms of lesion scoring and bacteriological isolation, than those of groups A and B. With the O18 challenge, only birds of group D presented a statistically significant reduction of their lesion score. To the authors’ knowledge, this is the first report on the efficacy of an immunization program in poultry that combines commercial and autogenous vaccines.

Common bacterial, viral, and parasitic diseases in pigeons (Columba livia): A review of diagnostic and treatment strategies

Pigeons (Columba livia) have been associated with humans for a long time now. They are raised for sport (pigeon race), exhibition (display of fancy breeds), food, and research. Most of the pigeons kept are Racing Homers, trained to compete in the pigeon race. Other breeds, such as Rollers, Nose Divers, Doneks are bred for their aerial abilities. Incorporation of a good preventive medicine program is one of the most critical factors in averting infectious diseases in pigeon flocks. This review summarizes the common bacterial, viral, and parasitic infections in pigeons. The different clinical signs, symptoms, diagnostic strategies, prevention, and treatments were described in this review. Current researches, molecular diagnostic assays, and treatment strategies such as vaccines and drug candidates were included. The information found in this review can provide insights for veterinarians and researchers studying pigeons to develop effective and efficient immunoprophylactic and diagnostic tools for pigeon diagnosis and therapeutics.

Efficacy of Live Attenuated Vaccine and Commercially Available Lectin Against Avian Pathogenic E. coli Infection in Broiler Chickens

In this study, the protective efficacy of an E. coli live attenuated vaccine was compared to the preventive administration of lectin preparation before the challenge. Two hundred broiler chicks were divided into eight equal groups. The first group was used as a negative control group. Three groups were vaccinated at day 1 with the avian colibacillosis live vaccine of which one group served as a vaccinated nonchallenged group. Another two groups were treated with lectin product (0.5 mL/L drinking water) for three days before the challenge. The last two groups served as challenge control for either E. coli O₇₈ or O₁₂₅ strains. The challenge was conducted at three weeks of age with either homologous O₇₈ or heterologous O₁₂₅E. coli strains, using 0.5 mL/bird of each avian pathogenic E. coli (APEC) strain (~10⁸ colony forming units “CFU”/mL)/subcutaneously. The bodyweight and feed conversion ratios (FCR) were calculated for four weeks. Clinical signs and gross and histopathological lesions were scored at two and seven days post inoculation (dpi). The heart and liver of euthanized chickens at 2 dpi were removed aseptically and homogenized to evaluate pathogenic E. coli colonization. Results showed that live avian colibacillosis vaccine reduced mortalities and APEC colonization in the homologous challenge group but not in the heterologous challenge group. Lectin-treated groups showed 20% and 16% mortality after challenge with E. coli O₇₈ and O₁₂₅, respectively, and both groups showed performance parameters, clinical signs, and histopathological lesion scores comparable to the negative control group, with variable E. coli colonization of heart and liver. The study demonstrated the efficacy of live attenuated avian colibacillosis vaccine against homologous but not heterologous APEC challenge in broiler chickens. The lectin-containing products can be used as a preventive medication to reduce the clinical impacts of colibacillosis regardless of the challenge strain. Standardization of the evaluation parameters for APEC vaccines is recommended.

Immunization with outer membrane vesicles of avian pathogenic Escherichia coli O78 induces protective immunity in chickens

Avian pathogenic Escherichia coli (APEC) typically causes colibacillosis and is a major concern for the poultry industry and public health. As a vaccine platform, the outer membrane vesicles (OMVs) derived from various gram-negative bacteria and even some gram-positive bacteria have been reported to be immunogenic in laboratories or upon commercial usage worldwide. Here, we purified OMVs from APEC serotype O78 strain by ultracentrifugation and gradient isolation. By SDS-PAGE and LC-MS/MS analysis, the 20 most abundant proteins located on OMVs were identified and analyzed; the lipopolysaccharide (LPS) profiles of OMVs were not different from those of the bacteria. Moreover, three groups of chickens were immunized with OMV-, outer membrane protein (OMP)- and PBS, with the latter two serving as positive and negative controls, respectively. By analyzing the anti-OMP and anti-LPS IgG titers stimulated by the tested vaccine candidates, the macrophage opsonophagocytic activity and the bactericidal activity mediated by serum antibodies in vaccinated chickens, we found that the OMV-vaccinated chicken group was superior to the two other groups. These findings were confirmed by additional chicken challenge tests, in which all OMV-vaccinated group chickens obtained complete protection but those of the other two groups were barely protected. Our data demonstrate that native APEC O78 OMVs can induce protective immunity in chickens and therefore be used as a candidate vaccine for APEC serotype O78 strain infections.

Efficacy of an avian colibacillosis live vaccine for layer breeder in Japan

Colibacillosis is one of an economically significant disease in the poultry industry, especially for meat breed chickens. Recently it has become a serious problem for layer especially when the birds start laying and also at the later stage of laying. In Japan, the productivity of field laying hens improved when the Δcrp avian colibacillosis live vaccine (“Gall N tect CBL”) was used. The survival rate and egg laying rate increased during almost all of the laying period when compared with the control group. The improvement in productivity was clearly demonstrated by comparing the number of eggs laid per day. The use of an avian colibacillosis live vaccine proved to be cost-effective in laying hens.

Avian pathogenic Escherichia coli ΔtonB mutants are safe and protective live-attenuated vaccine candidates

Avian pathogenic Escherichia coli (APEC) cause colibacillosis, a serious respiratory disease in poultry. Most APEC strains possess TonB-dependent outer membrane transporters for the siderophores salmochelin and aerobactin, which both contribute to their capacity to cause disease. To assess the potential of iron transport deficient mutants as vaccine candidates, the tonB gene was deleted in the APEC wild type strain E956 and a Δfur (ferric uptake repressor) mutant of E956. The growth of the ΔtonB and ΔtonB/Δfur mutants was impaired in iron-restricted conditions, but not in iron-replete media. Day old chicks were exposed to aerosols of the mutants to assess their efficacy as live attenuated vaccines. At day 18, the birds were challenged with aerosols of the virulent parent strain E956. Both mutants conferred protection against colibacillosis; weight gains and lesion scores were significantly different between the vaccinated groups and an unvaccinated challenged control group. Thus mutation of iron uptake systems can be used as a platform technology to generate protective live attenuated vaccines against extraintestinal E. coli infections, and potentially a range of Gram negative pathogens of importance in veterinary medicine.