Acapsular Pasteurella multocida B:2 can stimulate protective immunity against pasteurellosis

Deleting qseC downregulates virulence and promotes cross-protection in Pasteurella multocida

QseC, a histidine sensor kinase of the QseBC two-component system, acts as a global regulator of bacterial stress resistance, biofilm formation, and virulence. The function of QseC in some bacteria is well understood, but not in Pasteurella multocida. We found that deleting qseC in P. multocida serotype A:L3 significantly down-regulated bacterial virulence. The mutant had significantly reduced capsule production but increased resistance to oxidative stress and osmotic pressure. Deleting qseC led to a significant increase in qseB expression. Transcriptome sequencing analysis showed that 1245 genes were regulated by qseC, primarily those genes involved in capsule and LPS biosynthesis and export, biofilm formation, and iron uptake/utilization, as well as several immuno-protection related genes including ompA, ptfA, plpB, vacJ, and sodA. In addition to presenting strong immune protection against P. multocida serotypes A:L1 and A:L3 infection, live ΔqseC also exhibited protection against P. multocida serotype B:L2 and serotype F:L3 infection in a mouse model. The results indicate that QseC regulates capsular production and virulence in P. multocida. Furthermore, the qseC mutant can be used as an attenuated vaccine against P. multocida strains of multiple serotypes.

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.

Development of OMP based indirect ELISA to gauge the antibody titers in bovines against Pasteurella multocida

Pasteurella multocida (P. multocida) is an important pathogen of various domestic animals. The outer membrane proteins (OMPs) play a major role in pathogenesis and immunogenicity of P. multocida. The aim of the study was to develop indirect enzyme linked immuno sorbant assay (ELISA) based on OMPs to ascertain the antibody titers in animals post-infection or to gauge the potency of vaccine. The OMPs were extracted and purified from P. multocida P:52 (vaccine strain) and P. multocida B:2 isolated from natural outbreak of Haemorrhagic septicaemia (HS) and analyzed on SDS PAGE and through western blot. The OMPs profile of the vaccine strain and the isolate from the natural outbreak of HS were found to be similar. Optimization of various components viz. coating antigens, anti-species conjugate, etc. were carried out against both anti-P. multocida hyper immune and pre immune serum. Validation of OMP based indirect ELISA assay to measure immune response against P. multocida in bovine revealed 91% diagnostic sensitivity (DSN) and about 100% diagnostic specificity (DSP) at 25% cut off. OMP based indirect ELISA was found to be more specific, but less sensitive as compared to WCL based assay.

Development of immunization trials against Pasteurella multocida

Pasteurellosis is one of the most important respiratory diseases facing economically valuable farm animals such as poultry, rabbit, cattle, goats and pigs. It causes severe economic loss due to its symptoms that range from primary local infection to fatal septicemia. Pasteurella multocida is the responsible pathogen for this contagious disease. Chemotherapeutic treatment of Pasteurella is expensive, lengthy, and ineffective due to the increasing antibiotics resistance of the bacterium, as well as its toxicity to human consumers. Though, biosecurity measures played a role in diminishing the spread of the pathogen, the immunization methods were always the most potent preventive measures. Since the early 1950s, several trials for constructing and formulating effective vaccines were followed. This up-to-date review classifies and documents such trials. A section is devoted to discussing each group benefits and defects.

Screening of 71 P. multocida proteins for protective efficacy in a fowl cholera infection model and characterization of the protective antigen PlpE

Background

There is a strong need for a recombinant subunit vaccine against fowl cholera. We used a reverse vaccinology approach to identify putative secreted or cell surface associated P. multocida proteins that may represent potential vaccine candidate antigens.

Principal Findings

A high-throughput cloning and expression protocol was used to express and purify 71 recombinant proteins for vaccine trials. Of the 71 proteins tested, only one, PlpE in denatured insoluble form, protected chickens against fowl cholera challenge. PlpE also elicited comparable levels of protection in mice. PlpE was localized by immunofluorescence to the bacterial cell surface, consistent with its ability to elicit a protective immune response. To explore the role of PlpE during infection and immunity, a plpE mutant was generated. The plpE mutant strain retained full virulence for mice.

Conclusion

These studies show that PlpE is a surface exposed protein and was the only protein of 71 tested that was able to elicit a protective immune response. However, PlpE is not an essential virulence factor. This is the first report of a denatured recombinant protein stimulating protection against fowl cholera.

A review of hemorrhagic septicemia in cattle and buffalo

Hemorrhagic septicemia (HS), an acute, fatal and septicemic disease of cattle and buffaloes caused by Pasteurella multocida, is important in tropical regions of the world, especially in African and Asian countries. The prevalence of disease has been well documented with predominant isolation of P. multocida serotypes B:2 and E:2. Conventional methods of identification such as serotyping, biotyping, antibiogram determination and pathogenicity as well as molecular methods (P. multocida-specific polymerase chain reaction (PCR), a serogroup B-specific PCR assay, multiplex capsular typing system and loop-mediated isothermal amplification techniques) and characterization (restriction endonuclease analysis, randomly amplified polymorphic DNA analysis, repetitive extragenic palidromic PCR and enterobacterial repetitive intergenic consensus PCR analysis) are applied in parallel for rapid epidemiological investigations of HS outbreaks. Although several vaccine formulations including alum precipitated, oil adjuvant and multiple emulsion vaccines are commercially available, the quest for suitable broadly protective HS vaccines with long-lasting immunity is on the upsurge. Concurrently, attempts are being made to unravel the mysteries of the pathogen and its virulence factors, pathogenesis and determinants of protective immunity as well as diversity among strains of P. multocida. This review highlights the advances in these various aspects of HS.

Analysis of thePasteurella multocida outer membrane sub-proteome and its response to thein vivo environment of the natural host

This study describes the identification of outer membrane proteins (OMPs) of the bacterial pathogen Pasteurella multocida and an analysis of how the expression of these proteins changes during infection of the natural host. We analysed the sarcosine-insoluble membrane fractions, which are highly enriched for OMPs, from bacteria grown under a range of conditions. Initially, the OMP-containing fractions were resolved by 2-DE and the proteins identified by MALDI-TOF MS. In addition, the OMP-containing fractions were separated by 1-D SDS-PAGE and protein identifications were made using nano LC MS/MS. Using these two methods a total of 35 proteins was identified from samples obtained from organisms grown in rich culture medium. Six of the proteins were identified only by 2-DE MALDI-TOF MS, whilst 17 proteins were identified only by 1-D LC MS/MS. We then analysed the OMPs from P. multocida which had been isolated from the bloodstream of infected chickens (a natural host) or grown in iron-depleted medium. Three proteins were found to be significantly up-regulated during growth in vivo and one of these (Pm0803) was also up-regulated during growth in iron-depleted medium. After bioinformatic analysis of the protein matches, it was predicted that over one third of the combined OMPs predicted by the bioinformatics sub-cellular localisation tools PSORTB and Proteome Analyst, had been identified during this study. This is the first comprehensive proteomic analysis of the P. multocida outer membrane and the first proteomic analysis of how a bacterial pathogen modifies its outer membrane proteome during infection.

Vaccination against fowl cholera with acapsular Pasteurella multocida A:1

We have previously constructed an acapsular Pasteurella multocida X-73 (serogroup A) mutant strain which was attenuated in virulence for chickens (Chung JY, Wilkie IW, Boyce JD, Townsend KM, Frost AJ, Ghodussi M, Adler B. Role of capsule in the pathogenesis of fowl cholera caused by Pasteurella multocida serogroup A. Infect. Immun. 2001;69:2487-2492). In this study, we have assessed the ability of this acapsular strain (PBA930) to induce protection against wild-type challenge in mice and the natural host chickens. Intramuscular administration of PBA930 to mice stimulated significant protection against X-73 and the heterologous strain P-1059 (A:3), but not against challenge with P-1662 (A:4). No protection was observed when PBA930 was introduced by the intraperitoneal or subcutaneous routes in mice. Significantly, the acapsular strain PBA930 was able to induce protection against challenge with wild type X-73 in chickens.

Safety, efficacy and cross-protectivity of a live intranasal aerosol haemorrhagic septicaemia vaccine

The safety, efficacy and cross-protectivity of a live intranasal aerosol haemorrhagic septicaemia vaccine containing Pasteurella multocida serotype B:3,4 were tested in young cattle and buffaloes in Myanmar, where more than 1.5 million animals had been inoculated with this vaccine between 1989 and 1999. A recommended dose of 2 x 10(7) viable organisms was used for the efficacy test. The administration of 100 times the recommended dose to 50 cattle and 39 buffalo calves was innocuous. Seven months after they were vaccinated, three of three buffaloes were protected and 12 months after they were vaccinated, three of four buffaloes were protected against a subcutaneous challenge with serotype B:2 which killed three of three unvaccinated buffaloes. Twelve months after they were vaccinated, eight of eight cattle survived a serotype B:2 challenge, which killed four of four unvaccinated controls. The vaccinated cattle had developed serum antibodies detectable by the passive mouse protection test. Indirect haemagglutination tests on sera taken from cattle 10 days and five weeks after they were vaccinated showed high titres of antibodies. The serum of vaccinated cattle cross-protected passively immunised mice against infection with P. multocida serotypes E:2, F:3,4 and A:3,4.

Characterisation of bovine strains of Pasteurella multocida and comparison with isolates of avian, ovine and porcine origin

One hundred and fifty-three bovine Pasteurella multocida strains recovered primarily from cases of pneumonia and mastitis in England and Wales over an 11-year period were characterised by capsular PCR typing, comparison of outer membrane protein (OMP) profiles, and multilocus sequence analysis. All of the strains were of capsular type A with the exception of a single capsular type F isolate. Thirteen distinct OMP profiles (OMP-types) were identified based mainly on molecular mass heterogeneity of the heat-modifiable (OmpA) and porin (OmpH) proteins. However, 85% of the isolates were represented by just five OMP-types and 39% of the strains were of a single OMP-type. Multilocus sequence analysis revealed a limited degree of genetic diversity among bovine P. multocida isolates; strains of the same OMP-type have identical genetic backgrounds and represent distinct clones. Analysis of OMP variation was more discriminating than multilocus sequence analysis because strains of different OMP-types had the same, or similar, genetic backgrounds. The association of a small number of clones with the majority of cases of bovine pneumonia suggests that these clones have an increased capacity to cause disease compared to less frequently recovered clones. Molecular mass heterogeneity of OmpA and OmpH, in strains of the same or similar genetic background, suggests that these proteins are subject to diversifying selection within the host and might play important roles in host-pathogen interactions. Comparison of the OMP profiles of bovine isolates with those of avian, ovine and porcine strains showed that a high proportion of the respiratory tract infections in each of these species are caused by different strains of P. multocida. However, the presence of small numbers of closely related strains in more than one host species suggests that transmission of bacteria between different host species is also a factor in the population biology of P. multocida.