Identification of the Avian Pasteurella multocida phoP Gene and Evaluation of the Effects of phoP Deletion on Virulence and Immunogenicity

Whole genome characterization of a multidrug-resistant hypervirulent Pasteurella multocida with a new drug-resistant plasmid

Pasteurella multocida (P. multocida) is a zoonotic bacterium that can cause diseases in a variety of animals. It was divided into 5 serogroups, and serogroup A is mainly prevalent in avian hosts. We isolated a virulent and multidrug-resistant P. multocida strain from Guangdong duck liver and named it PMWSG-4 (GenBank accession no. CP077723.1). To understand the pathogenicity of this strain, the pathogenicity test was carried out with mice and ducks. The results showed that PMSWG-4 was highly pathogenic to ducks and mice, and the LD50 is 4.5 and 73 CFU, respectively. In order to study its genetic characteristics, pathogenicity, and relationship with the host, we performed a whole genome sequencing. The genome size of the isolated PMWSG-4 was 2.38 Mbp, with a G+C content of 40.3%, and coding 2,313 Coding DNA Sequence (CDS). The genome carries 162 potential virulence-associated genes, 32 different drug resistance phenotypes, 102 genes possibly involved in pathogen-host interaction, 2 gene island groups, and 4 prophages. In addition, we also found a new drug-resistant plasmid from strain PMWSG-4, named pXL001 (GenBank accession no. CP077724.1). After verified, the plasmid is a new plasmid carrying the floR florfenicol resistance gene. The whole genome is of great significance for further studying the pathogenesis and genetic characteristics of duck-derived P. multocida.

Immunogenicity and protective efficacy of the recombinant Pasteurella multocida lipoproteins VacJ and PlpE, and outer membrane protein H from P. multocida A:1 in ducks

Duck cholera (duck hemorrhagic septicemia) is a highly contagious disease caused by Pasteurella multocida, and is one of the major bacterial diseases currently affecting the duck industry. Type A is the predominant pathogenic serotype. In this study, the genes encoding the lipoproteins VacJ, PlpE, and the outer membrane protein OmpH of P. multocida strain PMWSG-4 were cloned and expressed as proteins in E. coli. The recombinant VacJ (84.4 kDa), PlpE (94.8 kDa), and OmpH (96.7 kDa) proteins were purified, and subunit vaccines were formulated with a single water-in-oil adjuvant, while killed vaccines were prepared using a single oil-coated adjuvant. Antibody responses in ducks vaccinated with recombinant VacJ, PlpE, and OmpH proteins formulated with adjuvants were significantly antigenic (p<0.005). Protectivity of the vaccines was evaluated via the intraperitoneal challenge of ducks with 20 LD50 doses of P. multocida A: 1. The vaccine formulation consisting of rVacJ, rPlpE, rOmpH, and adjuvant provided 33.3%, 83.33%, and 83.33% protection, respectively, the vaccine formulation consisting of three recombinant proteins, rVacJ, rPlpE, rOmpH and adjuvant, was 100% protective, and the killed vaccine was 50% protective. In addition, it was shown through histopathological examination and tissue bacterial load detection that all vaccines could reduce tissue damage and bacterial colonization to varying (p<0.001). These findings indicated that recombinant PlpE or OmpH fusion proteins formulated with oil adjuvants have the potential to be used as vaccine candidates against duck cholera subunits.

Virulence, immunogenicity and live vaccine potential of aroA and phoP mutants of Edwardsiella piscicida in zebrafish

Vaccination remains the most effective approach for prevention and control of infectious diseases in aquaculture. Edwardsiella piscicida is a causative agent of edwardsiellosis leading to mass mortality in a variety of fish species, leading to huge economic losses in the aquaculture industry. In this study, we have deleted the aroA and phoP genes in E. piscicida and investigated the phenotype, degrees of attenuation, immunogenicity, and ability to confer immune protection in zebrafish host. Our vaccine strain χ16028 with genotype ΔaroA11 ΔphoP12, showed significantly reduced growth, motility, biofilm formation and intracellular replication compared to the wild-type strain J118. In this regard, χ16028 exhibited retarded colonization and attenuation phenotype in zebrafish. Studies showed that χ16028 induced TLR4 and TLR5 mediated NF-kB pathway and upregulated cytokine gene expression i.e., TNF-α, IL-1β, IL-6, IL-8 and type-I IFN in zebrafish. Zebrafish immunized by intracoelomic injection (i.c.) with χ16028 showed systemic and mucosal IgM responses and protection against the wild-type E. piscicida i.c. injection challenge. However, the protection was only 25% in zebrafish following i.c. challenge. We speculate that our vaccine strain might be very attenuated; a booster dose may trigger better immune response and increase the percentage of survival to a more significant level.

Novel multi-strain probiotics reduces Pasteurella multocida induced fowl cholera mortality in broilers

Pasteurella multocida causes fowl cholera, a highly contagious poultry disease of global concern, causing significant ecological and economic challenges to the poultry industry each year. This study evaluated the effects of novel multi-strain probiotics consisting of Lactobacillus plantarum, L. fermentum, Pediococcus acidilactici, Enterococcus faecium and Saccharomyces cerevisiae on growth performance, intestinal microbiota, haemato-biochemical parameters and anti-inflammatory properties on broilers experimentally challenged with P. multocida. A total of 120 birds were fed with a basal diet supplemented with probiotics (10⁸ CFU/kg) and then orally challenged with 10⁸ CFU/mL of P. multocida. Probiotics supplementation significantly (P < 0.05) improved growth performance and feed efficiency as well as reducing (P < 0.05) the population of intestinal P. multocida, enterobacteria, and mortality. Haemato-biochemical parameters including total cholesterol, white blood cells (WBC), proteins, glucose, packed cell volume (PCV) and lymphocytes improved (P < 0.05) among probiotic fed birds when compared with the controls. Transcriptional profiles of anti-inflammatory genes including hypoxia inducible factor 1 alpha (HIF1A), tumor necrosis factor- (TNF) stimulated gene-6 (TSG-6) and prostaglandin E receptor 2 (PTGER2) in the intestinal mucosa were upregulated (P < 0.05) in probiotics fed birds. The dietary inclusion of the novel multi-strain probiotics improves growth performance, feed efficiency and intestinal health while attenuating inflammatory reaction, clinical signs and mortality associated with P. multocida infection in broilers.

The lipopolysaccharide outer core transferase genes pcgD and hptE contribute differently to the virulence of Pasteurella multocida in ducks

Fowl cholera caused by Pasteurella multocida exerts a massive economic burden on the poultry industry. Lipopolysaccharide (LPS) is essential for the growth of P. multocida genotype L1 strains in chickens and specific truncations to the full length LPS structure can attenuate bacterial virulence. Here we further dissected the roles of the outer core transferase genes pcgD and hptE in bacterial resistance to duck serum, outer membrane permeability and virulence in ducks. Two P. multocida mutants, ΔpcgD and ΔhptE, were constructed, and silver staining confirmed that they all produced truncated LPS profiles. Inactivation of pcgD or hptE did not affect bacterial susceptibility to duck serum and outer membrane permeability but resulted in attenuated virulence in ducks to some extent. After high-dose inoculation, ΔpcgD showed remarkably reduced colonization levels in the blood and spleen but not in the lung and liver and caused decreased injuries in the spleen and liver compared with the wild-type strain. In contrast, the ΔhptE loads declined only in the blood, and ΔhptE infection caused decreased splenic lesions but also induced severe hepatic lesions. Furthermore, compared with the wild-type strain, ΔpcgD was significantly attenuated upon oral or intramuscular challenge, whereas ΔhptE exhibited reduced virulence only upon oral infection. Therefore, the pcgD deletion caused greater virulence attenuation in ducks, indicating the critical role of pcgD in P. multocida infection establishment and survival.

l-Serine Lowers the Inflammatory Responses during Pasteurella multocida Infection

Pasteurella multocida causes a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found that l-serine levels were significantly decreased in murine lungs infected with P. multocida.

Pasteurella multocida causes a variety of infectious diseases in various species of mammals and birds, resulting in enormous economic loss to the modern livestock and poultry industry. However, the mechanism of host-pathogen interaction is unclear. Here, we found that l-serine levels were significantly decreased in murine lungs infected with P. multocida. Exogenous l-serine supplementation significantly increased the survival rate of mice and decreased the colonization of P. multocida in the lungs of mice. Notably, l-serine decreased the macrophage- and neutrophil-mediated inflammatory responses in mice during P. multocida infection.

Identification of Fur in Pasteurella multocida and the Potential of Its Mutant as an Attenuated Live Vaccine

Pasteurella multocida is a pathogenic microorganism that causes a variety of serious diseases in humans and animals worldwide. The global regulator gene, fur, plays an important role in pathogenesis and regulates the virulence of many bacteria. Here, we identified a fur gene in P. multocida by complementing a Salmonella Choleraesuis Δfur mutant, and characterized a fur mutant strain of P. multocida. The P. multocida Δfur mutant strain exhibited no significant differences in growth and outer membrane protein (OMP) profiles when the complemented strain was compared to the parent. Ducks were used as the model organism to determine the virulence and protection efficacy induced by Δfur mutant strain. Animal experiments showed that colonization by the mutant was decreased by oral infection of live Δfur mutant strain. The LD₅₀ of the ducks infected with the Δfur mutant was 146-fold higher than that of the ducks infected with the wild-type strain when administered through the oral route. Evaluation of the immunogenicity and protective efficacy of the Δfur mutant of P. multocida revealed strong serum IgY and bile IgA immune responses following oral inoculation with the Δfur strain. Ducks that were orally inoculated with the Δfur mutant strain demonstrated 62% protection efficacy against severe lethal challenge with the wild-type P. multocida. This study provides new insights into P. multocida virulence and the potential use of an attenuated vaccine against P. multocida.

A biologically conjugated polysaccharide vaccine delivered by attenuated Salmonella Typhimurium provides protection against challenge of avian pathogenic Escherichia coli O1 infection

Avian pathogenic Escherichia coli (APEC) causes avian airsacculitis and colibacillosis, resulting in significant economic loss to the poultry industry. O1, O2 and O78 are the three predominant serotypes. O-antigen of lipopolysaccharide is serotype determinant and highly immunogenic, and O-antigen polysaccharide-based vaccines have great potential for preventing bacterial infections. In this study, we utilized a novel yeast/bacterial shuttle vector pSS26 to clone the 10.8 kb operon synthesizing APEC O1 O-antigen polysaccharide. The resulting plasmid was introduced into attenuated Salmonella vaccines to deliver this O-antigen polysaccharide. O1 O-antigen was stably synthesized in attenuated Salmonella Typhimurium, demonstrated by slide agglutination, silver staining and western blot. Our results also showed that APEC O1 O-antigen produced in the Salmonella vaccines was attached to bacterial cell surfaces, and the presence of heterologous O-antigen did not alter the resistance to surface-acting agents. Furthermore, birds immunized orally or intramuscularly provided protection against the virulent O1 APEC challenge. Salmonella vaccines carrying APEC O1 O-antigen gene cluster also induced high IgG and IgA immune responses against lipopolysaccharide from the APEC O1 strain. The use of our novel shuttle vector facilitates cloning of large DNA fragments, and this strategy could pave the way for production of Salmonella-vectored vaccines against prevalent APEC serotypes.

The Enhancement of the Pasteurella's Bacterin by Propolis Extracts

BACKGROUND

Pasteurella multocida continues to pose a danger to prone farm and wild animals all over the world. Chemotherapeutic treatments are progressively losing their effectiveness, last for long time, and cost a lot of money, as well as being toxic to human consumers. Therefore, clearing the way for immunization as a big-wheel alternative against the economic grain. Yet, the vaccines available in the market do not confer the necessary protection against the pathogen. The integration of the well adjuvanted killed vaccine with the attenuated vaccines proved to offer an effective protection to the host animals. However, the bare use of the killed bacterin to provide protection from the possible harm of the live attenuated vaccine was doubtful.

METHODS

In the present study, propolis extracts were used to ameliorate the immunogenicity of the Pasteurella bacterin. The cellular and humoral activities were assessed for the different bacterin formulations.

RESULTS

Propolis extracts adjuvants proved to broaden and extend the IgG potency, as well as to induce a unique mucosal protection against the bacterium. Simultaneously it offered an anti-inflammatory effect that increased the tolerability to the bacterin. While the cellular activity was relatively reduced with propolis extracts.

CONCLUSION

These results confirm the effectiveness of the formulation of the bacterin with propolis to offer a potent homologous primary protection to the animals against the long-life use of the attenuated Pasteurella vaccines.

Recombinant attenuated Salmonella Typhimurium with heterologous expression of the Salmonella Choleraesuis O-polysaccharide: high immunogenicity and protection

Non-typhoidal Salmonella are associated with gastrointestinal disease worldwide and invasive disease in Africa. We constructed novel bivalent vaccines through the recombinant expression of heterologous O-antigens from Salmonella Choleraesuis in Salmonella Typhimurium. A recombinant Asd⁺ plasmid pCZ1 with the cloned Salmonella Choleraesuis O-antigen gene cluster was introduced into three constructed Salmonella Typhimurium Δasd mutants: SLT11 (ΔrfbP), SLT12 (ΔrmlB-rfbP) and SLT16 (ΔrfbP ∆pagL::TT araCP_BADrfbP). Immunoblotting demonstrated that SLT11 (pCZ1) and SLT12 (pCZ1) efficiently expressed the heterologous O-antigen. In the presence of arabinose, SLT16 (pCZ1) expressed both the homologous and heterologous O-antigens, whereas in the absence of arabinose, SLT16 (pCZ1) mainly expressed the heterologous O-antigen. We deleted the crp/cya genes in SLT12 (pCZ1) and SLT16 (pCZ1) for attenuation purposes, generating the recombinant vaccine strains SLT17 (pCZ1) and SLT18 (pCZ1). Immunization with either SLT17 (pCZ1) or SLT18 (pCZ1) induced specific IgG against the heterologous O-antigen, which mediated significant killing of Salmonella Choleraesuis and provided full protection against a lethal homologous challenge in mice. Furthermore, SLT17 (pCZ1) or SLT18 (pCZ1) immunization resulted in 83% or 50% heterologous protection against Salmonella Choleraesuis challenge, respectively. Our study demonstrates that heterologous O-antigen expression is a promising strategy for the development of multivalent Salmonella vaccines.

Feeding of waste milk to Holstein calves affects antimicrobial resistance of Escherichia coli and Pasteurella multocida isolated from fecal and nasal swabs

The use of milk containing antimicrobial residues in calf feeding programs has been shown to select for resistant fecal Escherichia coli in dairy calves. However, information is scarce about the effects of feeding calves waste milk (WM) on the prevalence of multidrug-resistant bacteria. The objective of this study was to determine the antimicrobial resistance patterns of fecal E. coli and nasal Pasteurella multocida isolates from calves fed either milk replacer (MR) or WM in 8 commercial dairy farms (4 farms per feeding program). Fecal and nasal swabs were collected from 20 ± 5 dairy calves at 42 ± 3.2 d of age, and from 10 of these at approximately 1 yr of age in each study farm to isolate the targeted bacteria. Furthermore, resistance of E. coli isolates from calf-environment and from 5 calves at birth and their dams was also evaluated in each study farm. Resistances were tested against the following antimicrobial agents: amoxicillin-clavulanic acid, ceftiofur, colistin, doxycycline (DO), enrofloxacin (ENR), erythromycin, florfenicol, imipenem, and streptomycin. A greater number of fecal E. coli resistant to ENR, florfenicol, and streptomycin and more multidrug-resistant E. coli phenotypes were isolated in feces of calves fed WM than in those fed MR. However, the prevalence of fecal-resistant E. coli was also influenced by calf age, as it increased from birth to 6 wk of age for ENR and DO and decreased from 6 wk to 1 yr of age for DO regardless of the feeding program. From nasal samples, an increase in the prevalence of colistin-resistant P. multocida was observed in calves fed WM compared with those fed MR. The resistance patterns of E. coli isolates from calves and their dams tended to differ, whereas similar resistance profiles among E. coli isolates from farm environment and calves were observed. The findings of this study suggest that feeding calves WM fosters the presence of resistant bacteria in the lower gut and respiratory tracts of dairy calves.

Identification of the crp gene in avian Pasteurella multocida and evaluation of the effects of crp deletion on its phenotype, virulence and immunogenicity

Background

Pasteurella multocida (P. multocida) is an important veterinary pathogen that can cause severe diseases in a wide range of mammals and birds. The global regulator crp gene has been found to regulate the virulence of some bacteria, and crp mutants have been demonstrated to be effective attenuated vaccines against Salmonella enterica and Yersinia enterocolitica. Here, we first characterized the crp gene in P. multocida, and we report the effects of a crp deletion.

Results

The P. multocida crp mutant exhibited a similar lipopolysaccharide and outer membrane protein profile but displayed defective growth and serum complement resistance in vitro compared with the parent strain. Furthermore, crp deletion decreased virulence but did not result in full attenuation. The 50 % lethal dose (LD₅₀) of the Δcrp mutant was 85-fold higher than that of the parent strain for intranasal infection. Transcriptome sequencing analysis showed that 92 genes were up-regulated and 94 genes were down-regulated in the absence of the crp gene. Finally, we found that intranasal immunization with the Δcrp mutant triggered both systematic and mucosal antibody responses and conferred 60 % protection against virulent P. multocida challenge in ducks.

Conclusion

The deletion of the crp gene has an inhibitory effect on bacterial growth and bacterial resistance to serum complement in vitro. The P. multocida crp mutant was attenuated and conferred moderate protection in ducks. This work affords a platform for analyzing the function of crp and aiding the formulation of a novel vaccine against P. multocida.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-016-0739-y) contains supplementary material, which is available to authorized users.