Outer membrane proteins of bovine Pasteurella multocida serogroup A isolates

Differences in pathogenicity and virulence-associated gene expression among Pasteurella multocida strains with high and low virulence in a lung tissue model

Pasteurella multocida capsular type A can cause a pulmonary infection, leading to serious pecuniary losses in cattle. The heterogeneity of infection outcome of P. multocida strains showing different virulence may be related to divergent expression of virulence genes. In this study, we compared the transcriptional response of virulence-associated genes in high (PMPAN001) and low (PMPAN007) virulence P. multocida capsular type A strains in lung tissues and in vitro. These clinical isolates differ in their organ bacterial loads, mRNA abundance of the same virulence genes between lung and culture medium, and extent of lung damage. Among the eight virulence-associated genes (fimA, tbpA, exbD, fur, oma87, pmHAS, nanH, and tonB), seven genes showed higher expression in lung compared with in vitro at 16 h (P ≤ 0.05) in PMPAN001, but not in PMPAN007. FimA, exbD, fur, oma87, pmHAS, and tonB gene transcripts showed significantly higher expression in PMPAN001 than in PMPAN007 in the lung tissues at 16 h post-infection (P ≤ 0.05). Specially, the virulence gene, nanH, in both strains was associated with poor expression in vitro and lung tissue (mean relative mRNA abundance values < 0.6). Strain PMPAN001 had a higher proliferation rate in vivo than strain PMPAN007. The bacterial loads of PMPAN001 in the organs increased from 12 h post-infection, with maximum bacteria count ranging from 1 million to 20 million/mg. In addition, lungs treated with PMPAN001 produced serious and extensive lesions marked with inflammation at 20 h. Overall, our results reveal that the highly expressed virulence-associated genes, fimA, exbD, fur, oma87, pmHAS, and tonB can be used as markers for assessing the virulence of P. multocida capsular type A strains.

Genome Sequence of a Bovine Isolate of Pasteurella multocida Strain 232

We present here the genome sequence of Pasteurella multocida 232, a bacterium that is associated with pneumonia in humans as well as in many animal species. The genome of Pasteurella multocida 232 has an N₅₀ value of 187.32 kb and a total size of 2.34 Mb.

We present here the genome sequence of Pasteurella multocida 232, a bacterium that is associated with pneumonia in humans as well as in many animal species. The genome of Pasteurella multocida 232 has an N₅₀ value of 187.32 kb and a total size of 2.34 Mb.

Expression patterns and role of SDF-1/CXCR4 axis in boar spermatogonial stem cells

The signaling of chemokine stromal cell-derived factor (SDF)-1 and its receptor C-X-C motif chemokine receptor 4 (CXCR4) is involved in the cellular proliferation, survival, and migration of various cell types. Although SDF-1/CXCR4 has been implicated in the maintenance of the spermatogonial population during mouse testis development, their expression patterns and functions in boar testis remain unclear. In the present study, the expression pattern of SDF-1 and CXCR4 was determined during pre-pubertal and post-pubertal stage boar testes and in vitro cultured porcine spermatogonial stem cells (pSSCs). The role of these proteins in colony formation in cultured pSSCs was also investigated. Interestingly, SDF-1 expression was observed in PGP 9.5-positve spermatogonia in all developing stages of boar testis; however, CXCR4 expression was only detected in spermatogonia from 5-day-old boar testis. In addition, SDF-1 and CXCR4 expression was observed in cultured pSSCs from 5-day-old boar testes, and inhibition of the CXCR4 receptor signaling pathway by AMD3100 significantly decreased the colony formation of pSSCs. These results suggest that SDF-1 and CXCR4 are useful markers for detecting stage-specific spermatogonia in boar testis. Our results reveal the role of the SDF-1/CXCR4 axis in pSSC in vitro culture.

The relationship between capsular type and OmpA of Pasteurella multocida is associated with the outcome of disease

The genes encoding OmpA of Pasteurella multocida recovered from diseased and apparently healthy animals have been characterized. The nucleotide sequence revealed ORFs of 1047-1077 bp encoding proteins of 349-360 amino acids. Domain analysis of OmpA showed signal peptide, N-terminal ompA domain and C-terminal ligand binding domain. The transmembrane topology of OmpA showed short turns at the periplasmic end and longer irregular loops at the extracellular end. The phylogenetic analysis based on OmpA showed affiliation of isolates to 7 groups representing different alleles. The identical segments in OmpA also suggested assortative recombination within classes IV, V and VI of distinct lineages. Principal component analysis separated isolates into groups based on capsular type and PmompA alleles. The alleles belonging to class VI exclusively associated with capsular type A, whereas class I-IV were associated with capsular type B. PmompA alleles in class V were recorded in both serogroups. PmompA6.1, 6.4 were distributed among strains with capsular type A, and PmompA6.2 and 6.3 among capsular type B. Despite internal OmpA variabilty, restrictive and well defined distribution was seen amongst P. multocida. A definitive association of "OmpA-capsular type" was observed with clinical status of animals. A cohort of pasteurellae comprising of OmpA(I-IV)-capB was recovered from diseased animals and OmpA(VI)-capA from healthy subjects. This study concludes that P. multocida with serogroup A and B from healthy and diseased animals represent distinct clusters also differentiated based on their OmpA-types and OmpA-capsular type relationship possibly determine the virulence and disease outcome.

Virulence genotyping of Pasteurella multocida isolated from multiple hosts from India

In this study, 108 P. multocida isolates recovered from various host animals such as cattle, buffalo, swine, poultry (chicken, duck, and emu) and rabbits were screened for carriage of 8 virulence associated genes. The results revealed some unique information on the prevalence of virulence associated genes among Indian isolates. With the exception of toxA gene, all other virulence associated genes were found to be regularly distributed among host species. Association study between capsule type and virulence genes suggested that pfhA, nanB, and nanH genes were regularly distributed among all serotypes with the exception of CapD, whereas toxA gene was found to be positively associated with CapD and CapA. The frequency of hgbA and nanH genes among swine isolates of Indian origin was found to be less in comparison to its equivalents around the globe. Interestingly, very high prevalence of tbpA gene was observed among poultry, swine, and rabbit isolates. Likewise, very high prevalence of pfhA gene (95.3%) was observed among Indian isolates, irrespective of host species origin.

Serum antibody responses in horses and mice following immunization with Actinobacillus equuli outer membrane proteins and recombinant Aqx toxin

The immune responsiveness of mice (without prior natural exposure) and mares (with naturally acquired antibodies) was determined following vaccination with Actinobacillus equuli outer membrane proteins (OMPs) and/or recombinant A. equuli toxin (rAqx). Mice were vaccinated subcutaneously on days 0 and 21 with one of three doses (5, 25 or 50μg) of A. equuli OMPs, rAqx or both, together with Freund's incomplete adjuvant (FIA). Antibodies against formalin-killed whole bacterial cells (WBCs), OMPs and Aqx were determined on days 0, 21 and 42. Mares were vaccinated subcutaneously on days 0 and 21 with 100μg OMPs, 100μg rAqx or a combination of 50μg of each antigen, together with FIA. Antibodies against WBCs, OMPs and Aqx were determined at 7day intervals for the first 42days, as well as on days 56, 70, 154 and 238. Vaccination of mice stimulated an apparent dose response to OMPs and Aqx. Antibodies against OMPs and Aqx were enhanced following vaccination of mares that had naturally acquired pre-existing antibodies. There was no evidence of interference with antibody responses to the individual antigens when OMPs and rAqx were combined prior to vaccination.

Comparison of genotypic and phenotypic characterization methods for Pasteurella multocida isolates from fatal cases of bovine respiratory disease

Bovine respiratory disease (BRD) is the most costly disease of beef cattle in North America. Because Pasteurella multocida is a commensal of the upper respiratory tract, it is generally considered an opportunistic pathogen. However, studies in swine indicated that there may be a limited number of strains associated with disease, suggesting that some are more virulent than others. Although this may also be true of isolates from cattle, appropriate typing methods must be established before this possibility can be investigated. The purpose of this study was to compare effectiveness of polymerase chain reaction (PCR) fingerprinting to more traditional approaches for typing bovine P. multocida isolates. Isolates were obtained from 41 cases of fatal BRD and subjected to random amplified polymorphic DNA PCR (RAPD-PCR), whole cell protein (WCP) profiles, outer membrane protein (OMP) profiles, and serotyping. The discrimination index was calculated for each typing method and combinations of each using Simpson's index of diversity. Correlation coefficients were calculated to assess concordance between classification results achieved through genotypic (RAPD-PCR) and phenotypic (WCP, OMP, and serotyping) approaches. All characterization methods were capable of discriminating between isolates. However, there was poor concordance between techniques. There were also few significant associations between typing results and epidemiologic data. Random amplified polymorphic DNA PCR was validated as being a repeatable and reliable means of discriminating between P. multocida isolates obtained from cattle. Isolates obtained from fatal cases of BRD in calves in a commercial feedlot demonstrated significant diversity, justifying additional investigation into whether P. multocida is a strictly opportunistic pathogen in cattle.

Pasteurella multocidaand bovine respiratory disease

Pasteurella multocidais a pathogenic Gram-negative bacterium that has been classified into three subspecies, five capsular serogroups and 16 serotypes.P. multocidaserogroup A isolates are bovine nasopharyngeal commensals, bovine pathogens and common isolates from bovine respiratory disease (BRD), both enzootic calf pneumonia of young dairy calves and shipping fever of weaned, stressed beef cattle.P. multocidaA:3 is the most common serotype isolated from BRD, and these isolates have limited heterogeneity based on outer membrane protein (OMP) profiles and ribotyping. Development ofP. multocida-induced pneumonia is associated with environmental and stress factors such as shipping, co-mingling, and overcrowding as well as concurrent or predisposing viral or bacterial infections. Lung lesions consist of an acute to subacute bronchopneumonia that may or may not have an associated pleuritis. Numerous virulence or potential virulence factors have been described for bovine respiratory isolates including adherence and colonization factors, iron-regulated and acquisition proteins, extracellular enzymes such as neuraminidase, lipopolysaccharide, polysaccharide capsule and a variety of OMPs. Immunity of cattle against respiratory pasteurellosis is poorly understood; however, high serum antibodies to OMPs appear to be important for enhancing resistance to the bacterium. Currently availableP. multocidavaccines for use in cattle are predominately traditional bacterins and a live streptomycin-dependent mutant. The field efficacy of these vaccines is not well documented in the literature.

Serum antibodies in mares and foals to Actinobacillus equuli whole cells, outer membrane proteins, and Aqx toxin

Actinobacillus equuli is carried in the alimentary tract of mares and can cause severe septicemia of neonatal foals. A hemolytic subspecies, A. equuli subsp. haemolyticus, and a non-hemolytic subspecies, A. equuli subsp. equuli, have been identified. Hemolytic strains produce the RTX toxin Aqx. The purpose of this study was to demonstrate sequentially in two sets of mare-foal pairs antibodies to A. equuli whole bacterial cells, outer membrane proteins, and recombinant Aqx and to compare the transfer of antibodies to these antigens between mares and their foals. Two mare/foal sets of sera were evaluated. Cohort A consisted of 18 mare-foal pairs obtained in the spring of 2005. Cohort B consisted of 10 mare-foal pairs obtained in the spring of 2006. For both sets, mare and foal sera were obtained immediately after foaling and prior to nursing (time 0) as well as at 12 and 24h and daily thereafter for 7 days. For Cohort B, sera were also obtained 30 days after birth. At parturition all mares had detectable antibodies to A. equuli whole cells and outer membranes; however, of those mares, two in Cohort A had undetectable antibodies to Aqx and their foals likewise had undetectable anti-Aqx antibodies. Antibodies against whole cells, outer membrane proteins, and Aqx were readily transferred from mares to foals. In most cases, there were significant correlations (p<0.05) between antibodies against whole cells, outer membrane proteins, and Aqx in mares' sera at the time of parturition and foal sera 24 after birth. Antibodies against the three antigen preparations had declined insignificantly (p>0.05) by day 30.

Immunization with Outer Membrane Proteins of Pasteurella multocida (6:B) Provides Protection in Mice

The immunoprotective efficacy of Pasteurella multocida (6:B) outer membrane proteins (OMPs) was examined in the mouse model. Bacterial OMPs were extracted using sarkosyl method and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting. Prototype vaccines were prepared using OMPs with adjuvants including dioleoyl phosphatidyl choline-based liposome and Montanide ISA206 water-in oil-in water emulsion. Antibody response to the vaccine was monitored using indirect enzyme linked immunosorbent assay. The results of the study showed that immunized mice had high titre with both the formulations. The vaccinated mice were able to survive a live virulent bacterial challenge. Based on the findings of the study it can be inferred that OMPs are important determinants of immunoprotection hence can serve as vaccine candidates against haemorrhagic septicaemia.

Binding of Bartonella henselae to extracellular molecules: Identification of potential adhesins

Bartonella henselae, the etiologic agent of cat scratch disease, bacillary angiomatosis and other clinical syndromes initiates infection through a trauma or wound to the skin suggesting involvement of extracellular matrix molecules. We have demonstrated in this study that B. henselae bound strongly fibronectin, collagen IX and X, but comparatively less laminin and collagen IV. B. henselae bound primarily the N- and C-terminal heparin (Hep-1 and Hep-2, respectively) and the gelatin-binding domains of fibronectin (Fn) but not the cell-binding domain. Binding to the Hep-binding domain was significantly inhibited by Hep suggesting common binding sites on the Fn molecule. Furthermore, glycosaminoglycans-mediated binding of B. henselae to soluble Fn showed that Hep but not dextran sulfate inhibited the bacterium binding to Fn. Unlike Fn, B. henselae bound strongly vitronectin only in the presence of Hep or dextran sulfate. Also, the binding of B. henselae to host cells could be inhibited by anti-B. henselae surface-reactive antibodies, the exogenous Fn or the anti-Fn polyclonal antibodies. Ligand blots, batch affinity purification and MALDI-TOF peptide fingerprinting identified B. henselae Pap31, Omp43 and Omp89 as the three major putative Fn-binding proteins (FnBPs) in B. henselae outer membrane proteins. We hypothesized that B. henselae wound associated infections involved interactions with extracellular matrix molecules. Taken together, the above data suggest that interactions between B. henselae and ECM molecules such as Fn may play an important role in the bacterium adherence to and invasion of host cells.

Maternally and naturally acquired antibodies to Mannheimia haemolytica and Pasteurella multocida in beef calves

The dynamics and duration of maternally derived antibodies as well as the onset of acquired immunity against Mannheimia haemolytica and Pasteurella multocida in range-pastured beef calves were investigated. Two groups of unvaccinated cattle were used in this study. Serum antibody responses were measured by enzyme-linked immunoassay for antibodies of the IgG1, IgG2 and IgM isotypes binding M. haemolytica whole cells (WC) or leukotoxin (LKT) and P. multocida outer membrane proteins (OMPs). Comparisons of mean antibody responses to M. haemolytica LKT and WC and P. multocida OMPs were made within each group. Maternally derived antibodies against M. haemolytica and P. multocida reached lowest levels at 30-90 days after birth. Calves began production of antibodies against M. haemolytica and P. multocida between 60 and 90 days of age in both groups. Based on the results of this study, in beef herds vaccinated against M. haemolytica and/or P. multocida, it may be best to vaccinate calves around 3 months of age. In contrast, beef calves from unvaccinated herds might benefit from vaccination at 4 months of age.

Bartonella henselae Pap31, an extracellular matrix adhesin, binds the fibronectin repeat III13 module

Bartonella henselae wound-associated infections suggest involvement of extracellular matrix molecules in adhesion and invasion. Pap31 was previously identified as a hemin-binding protein. Our recent studies suggest the protein is an adhesin that is recognized by the host's immune systems. In this study we examined the interactions of B. henselae Pap31 with fibronectin (Fn), heparin (Hep), and human umbilical vein endothelial cells (HUVECs). The cloned gene was expressed in Escherichia coli, and the purified Pap31 protein elicited strong antibody responses in mice and was reactive with rabbit anti-live B. henselae and mouse anti-Pap31 antibodies by Western blotting. Pap31 bound to immobilized Fn and to HUVECs in a dose-dependent manner and to Hep. Fn fragment-binding assays identified the Hep-1 and Hep-2 binding domains of human Fn and in particular the (12-13)FnIII repeat module as primary binding sites for this adhesin. Furthermore, Pap31 binding to the above Fn fragments could be inhibited by Hep, suggesting a common binding site involving the 13FnIII repeat module on the Hep-2 domain of Fn. Adherence of intact B. henselae to HUVECs was inhibited by increasing concentrations of anti-Pap31 antibodies. In addition, purified Pap31 coprecipitated effectively with Fn and anti-Fn antibodies. Taken together, these data suggest that Pap31 is an Fn-binding protein mediating the B. henselae-host interaction(s), and they implicate the 13FnIII repeat module as an important binding site for this adhesin on the Fn molecule. These interactions may be important initial steps leading to bacterial attachment and colonization that promote the establishment of B. henselae infections in vivo.

Immunogenicity of iron-regulated outer membrane proteins of Pasteurella multocida A:3 in cattle: molecular characterization of the immunodominant heme acquisition system receptor (HasR) protein

The iron-regulated outer membrane proteins (IROMPs) of Pasteurella multocida A:3 strain 232 (Pm232), a bovine isolate, were investigated as potential immunogens in cattle. We addressed the ability of P. multocida IROMP-enriched fractions to induce antibody responses in cattle by different vaccination strategies and the protective efficacy of these antibodies using a P. multocida-induced pneumonia challenge model. Vaccination of cattle with outer membrane-enriched fractions derived from Pm232 grown on either iron-depleted (IROMPs) or iron-sufficient (OMPs) conditions induced significant antibody responses; however, the correlation with lung lesion scores was not significant (P = 0.01 and P < 0.07, respectively). SDS-PAGE, Western blots and densitometric analyses of Pm232 grown under iron-deficient conditions revealed five major IROMPs including an immunodominant 96 kDa protein band. Mass spectrometry analysis of the 96kDa protein band suggested homology with the heme acquisition system receptor (HasR) of avian P. multocida (strain Pm70) and was confirmed by DNA sequence analysis of the cloned Pm232 hasR gene. Further analyses indicated that Pm232 HasR is a surface-exposed OMP and conserved among most P. multocida isolates investigated. In addition, cattle vaccinated with live Pm232 or IROMPs had significantly higher antibody responses to the 96 kDa protein band and the correlation with lung lesion scores approached significance (P = 0.056). These results indicate that antibody responses in cattle are induced by P. multocida IROMPs, and that the 96 kDa HasR protein is an immunodominant IROMP.

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.

Molecular and immunological characterization of Pasteurella multocida serotype A:3 OmpA: evidence of its role in P. multocida interaction with extracellular matrix molecules

Pasteurella multocida OmpA-like gene (PmOmpA) was cloned and characterized. The mature protein had a molecular mass of 35,075 Da and significant similarity with Escherichia coli (E. coli) OmpA proteins. Membrane topology analyses predict that like E. coli OmpA, the N-terminal half of PmOmpA exists as an eight-stranded transmembrane antiparallel beta-barrel that displays four variable hydrophilic and surface-exposed regions with predicted antigenic peaks that may be involved in serum resistance or adherence. In addition, the Ala-Pro repeat region between the N-terminal beta-barrel and C-terminal periplasmic domains is completely missing in PmOmpA. PmOmpA was expressed in E. coli and immunoblots analysis revealed that the recombinant PmOmpA was immunogenic, and expressed in vivo. The binding of PmOmpA to biotinylated Madin Darby bovine kidney (MDBK) cells surface proteins, fibronectin and heparin was demonstrated. Furthermore, PmOmpA binds MDBK monolayers and pre-treatment of P. multocida whole cells with anti-PmOmpA significantly reduced adherence to fibronectin. Ligand blot analysis revealed that fibronectin binds to the native and heat modified forms of PmOmpA when heated at 37 and 100 degrees C, respectively. Collectively these data indicate that PmOmpA may be involved in P. multocida 232 adherence to host cells via heparin and/or fibronectin bridging.

Characterization of, and immune responses of mice to, the purified OmpA-equivalent outer membrane protein of Pasteurella multocida serotype A:3 (Omp28)

Pasteurella multocida A:3 is a major cause of bovine pneumonia. A major antigenic heat-modifiable 28kDa outer membrane protein (Omp28) was previously identified. The purpose of this study was to purify and characterize Omp28 immunologically and structurally. Omp28 was extracted from N-lauroylsarcosine-insoluble protein preparations by a combination of detergent fractionation with Zwittergent 3-14 and chromatography. Partial N-terminal amino acid sequence confirmed Omp28 as a member of the OmpA-porin family. However, porin activity could not be demonstrated in a lipid-bilayer assay. Heat modifiability of purified Omp28 was demonstrated, and Omp28 was found in outer membrane fraction of P. multocida. Surface exposure of Omp28 was demonstrated by partial protease digestion of intact bacteria, by binding of anti-Omp28 polyclonal ascites fluid to the bacterial surface, and by partial inhibition of anti-outer membrane antiserum binding by previous incubation of the bacteria with anti-Omp28 serum. CD-1 mice vaccinated with purified Omp28 developed a significant antibody titer (P<0.05) compared to the control treatment group but were not protected from a homologous intraperitoneal bacterial challenge. By contrast, treatment groups vaccinated with P. multocida outer membrane, formalin-killed P. multocida or a commercial vaccine were significantly protected from challenge. In vitro complement-mediated killing of P. multocida was observed in post-vaccination sera of outer membrane, formalin-killed P. multocida, and commercial vaccine-treatment groups, but not with sera from the Omp28-treatment group. In conclusion, although Omp28 is surface exposed and antigenic, it may not be a desirable immunogen for stimulating immunity to P. multocida.

Intranasal vaccination of rabbits with Pasteurella multocida A:3 outer membranes that express iron-regulated proteins

OBJECTIVE

To determine efficacy of intranasal vaccination of rabbits with Pasteurella multocida A:3 outer membrane proteins (OMP) expressing iron-regulated OMP (IROMP) in conferring protection against experimental challenge exposure.

ANIMALS

52 male New Zealand White rabbits.

PROCEDURE

Rabbits were vaccinated intranasally on days 0, 7, and 14; some vaccines included cholera toxin (CT) as an adjuvant. Concentrations of intranasal IgA and serum IgG antibodies against P multocida OMP were determined. In experiment A, rabbits were vaccinated with either phospate-buffered saline solution (PBSS), PBSS-CT, OMP-CT, or IROMP-CT, challenge-exposed intranasally on day 16, and euthanatized and necropsied on day 28. Rabbits were also vaccinated with OMP or IROMP without CT and were not challenge-exposed. In experiment B, rabbits were vaccinated with PBSS, PBSS-CT, IROMP, or IROMP-CT. On day 17, rabbits were challenge-exposed intranasally. Nasal bacteria and antibodies were determined on day 24.

RESULTS

In experiment A, OMP-CT vaccination stimulated mucosal and systemic antibody responses to the bacterium and enhanced resistance against challenge exposure. Intranasal bacterial counts were not significantly reduced. Vaccination with IROMP-CT stimulated mucosal and systemic antibodies, enhanced resistance to challenge exposure, and significantly reduced nasal bacterial counts. In experiment B, natural infection was detected in several rabbits at challenge exposure; however, IROMP-CT-vaccinated rabbits had significantly higher serum and nasal antibody responses, compared with other rabbits IROMP-CT-vaccinated rabbits had significantly lower nasal bacterial counts compared to control rabbits.

CONCLUSIONS AND CLINICAL RELEVANCE

Intranasal vaccination of rabbits with P multocida outer membranes containing IROMP and CT stimulated immunity against experimental pneumonic pasteurellosis.

Single primer polymerase chain reaction fingerprinting for Pasteurella multocida isolates from laboratory rabbits

OBJECTIVE

To evaluate a rapid polymerase chain reaction (PCR) fingerprinting technique for discriminating among Pasteurella multocida isolates from laboratory rabbits.

SAMPLE POPULATION

33 P multocida isolates from rabbits with clinical pasteurellosis.

PROCEDURE

PCR assays were conducted with 2 minisatellites (core sequence and modified core sequence of phage M13) and 2 microsatellites ([GTG]5 and [GACA]4). Each bacterium was assigned to a PCR type for each of the primers used. Boiled bacterial extracts and purified genomic DNA were compared by use of PCR assays for phage M13 and (GACA)4. Plasmids were isolated from each bacterium, and their influence on PCR fingerprint was determined, using boiled extracts as a DNA source.

RESULTS

M13 core sequence and M13 modified core sequence yielded 5 and 8 PCR types, respectively. The microsatellites (GTG)5 and (GACA)4 yielded 4 and 9 PCR fingerprint types, respectively. Fingerprint patterns obtained by use of isolated DNA differed from those obtained by use of boiled extracts, although discrimination among P multocida isolates was similar. The presence or absence of plasmids did not affect PCR fingerprints.

CONCLUSION

Single primer PCR fingerprinting with minisatellite and microsatellite primers is an efficient and reproducible method for the discrimination of P multocida isolates from rabbits and can be performed directly, using boiled bacterial extracts as a source of template, although more bands were obtained from pure genomic DNA.

The virulence and protective efficacy for chickens of pasteurella multocida administered by different routes

The relative virulence for chickens of five strains of Pasteurella multocida was evaluated. Twenty groups, each of ten chickens, were inoculated with a standard dose of 10(5) of each of five strains by the intramuscular (I.m.), intravenous (I.v.), intratracheal (I.tr.) or conjunctival (Co) routes. The highest mortality occurred in the groups dosed I.m. and I.v., followed by I.tr. inoculation. The relative virulence of each strain did not change when inoculated by the different routes. The most virulent strain, VP161, caused 100% mortality by all except the Co route. The least virulent strain, VP17, caused a single mortality by the I.v. route, but gave a high level of protection to birds inoculated by both the I.m. and I.v. routes, when challenged by intramuscular injection with (VP161). There was no protection against I.m. challenge in the birds inoculated by the I.tr. or Co routes. Serum antibody levels measured by ELISA correlated with the level of protection against virulent challenge for groups inoculated I.m. or I.v., but not I.tr. Western blots of pooled sera from each group did not show any specific antigen recognition that might explain the observed differences in protection. Inoculation with strain VP17, (both I.m. and I.tr.) also gave a high level of protection to birds challenged with strain VP161 by intratracheal instillation.