Relationship between the iron regulated outer membrane proteins and the outer membrane proteins of in vivo grown Pasteurella multocida

Effect of conditioned media from Aeromonas caviae on the transcriptomic changes of the porcine isolates of Pasteurella multocida

Background

Pasteurella multocida is an opportunistic pathogen causing porcine respiratory diseases by co-infections with other bacterial and viral pathogens. Various bacterial genera isolated from porcine respiratory tracts were shown to inhibit the growth of the porcine isolates of P. multocida. However, molecular mechanisms during the interaction between P. multocida and these commensal bacteria had not been examined. 

Methods

This study aimed to investigate the interaction between two porcine isolates of P. multocida (PM2 for type D and PM7 for type A) with Aeromonas caviae selected from the previously published work by co-culturing P. multocida in the conditioned media prepared from A. caviae growth and examining transcriptomic changes using RNA sequencing and bioinformatics analysis. 

Results

In total, 629 differentially expressed genes were observed in the isolate with capsular type D, while 110 genes were significantly shown in type A. High expression of genes required for energy metabolisms, nutrient uptakes, and quorum sensing were keys to the growth and adaptation to the conditioned media, together with the decreased expression of those in the unurgent pathways, including translation and antibacterial resistance.

Conclusion

This transcriptomic analysis also displayed the distinct capability of the two isolates of P. multocida and the preference of the capsular type A isolate in response to the tough environment of the A. caviae conditioned media. Therefore, controlling the environmental sensing and nutrient acquisition mechanisms of P. multocida would possibly prevent the overpopulation of these bacteria and reduce the chance of becoming opportunistic pathogens.

Immunopotential of Pasteurella multocida bivalent outer membrane protein-based vaccine entrapped in aluminum hydroxide nanoparticles

Swine pasteurellosis is one of the most economically important diseases of pig caused by Pasteurella multocida (P. multocida) capsular types A and D. These organisms are commensals and opportunistic pathogens in the upper respiratory tract in pig. In the present study, we extracted whole outer membrane proteins (OMP) from P. multocida capsular types A and D and were mixed together in the ratio of 1:1 forming bivalent outer-membrane proteins. The bivalent OMP was adsorbed onto aluminum hydroxide nanoparticles. The size of aluminum hydroxide nanoparticles adsorbed outer membrane protein was found to be in the range of 125 to 130 nm. We observed that aluminum hydroxide nanoparticles adjuvanted bivalent OMP-based vaccine elicited quicker immune kinetics in terms of IgG response as compared to aluminum hydroxide microparticles adjuvanted bivalent bacterin vaccine against P. multocida capsular type A and D.

Development of novel iron-regulated Pasteurella multocida B: 2 bacterin and refinement of vaccine quality in terms of minimum variation in particle size and distribution vis-a-vis critical level of iron in media

To enhance the qualitative bacterial biomass per unit of media and to overcome the limitations of the existing haemorrhagic septicaemia (HS) vaccines, a comprehensive study was undertaken encompassing the role of iron on the bacterial biomass of Pasteurella multocida B: 2 to vaccine development. Trypsin digested hydrochloric acid-treated sheep blood (THSB) as a novel iron rich supplement had been devised for the first time for augmenting the qualitative bacterial biomass per unit of media which was evident with growth kinetic study. The higher recovery of iron from THSB became evident via atomic absorbance spectrophotometry. The critical level of iron in the media as well as mode of iron supplementation showed a major impact on the outer membrane protein profile of P. multocida B:2 and variation in droplet size and particle-size distribution of formulated vaccine. Immune response study against iron-regulated bacterin adjuvanted with aluminum hydroxide gel in mouse model showed that 3% THSB supplementation of casein sucrose yeast (CSY) not only augmented the growth of P. multocida B:2 significantly but conferred highest pre-challenged ELISA IgG titer and protection against pasteurellosis. Thus, THSB supplementation of CSY can resolve existing up-scaling and immunogenic potential problems of HS vaccine production.

Protection of chickens against fowl cholera by supernatant proteins of Pasteurella multocida cultured in an iron-restricted medium

Pasteurella multocida (P. multocida), a causative agent of fowl cholera, is an important pathogen in the poultry industry. In the present study, we found that the inactivated vaccine of P. multocida grown in an iron-restricted medium provided better protection than that grown in normal medium. Thus, we adopted a comparative proteomics approach, by using two-dimensional gel electrophoresis (2-DE), coupled with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/TOF MS), to profile the supernatant proteins associated with P. multocida under both conditions. Eleven upregulated proteins were identified, including aspartate ammonia-lyase (AspA), diacylglycerol kinase (DgK), 30S ribosomal protein S6 (RpsF), and eight outer membrane proteins (OMPs). To further characterize the three novel supernatant proteins identified under iron-restricted conditions, the AspA, DgK and RpsF proteins were expressed and purified, and used as immunogens to vaccinate chickens. The results showed that AspA, DgK and RpsF proteins induced 80.0%, 66.7%, and 80.0% immunity, respectively. These data indicate that the three novel proteins identified in the supernatant of the culture media might play important roles in the survival of bacteria under iron-restricted conditions, and thus protect chickens against P. multocida. These findings also suggest that the proteins identified can be used as subunit vaccines.

Efficacy of bacteriophage Lysed Pasteurella marker vaccine in laboratory animal models with a novel DIVA for haemorrhagic septicaemia

OBJECTIVE

The present study aimed at evaluating the efficacy of an improved phage lysate marker vaccine for haemorrhagic septicaemia in mice and rabbit model and development of a DIVA ELISA based on iron restricted outer membrane protein (IROMP).

METHOD

The experimental vaccine was prepared by lysing P. multocida B:2 grown under iron restricted conditions with a Pasteurella bacteriophage and addition of an alum adjuvant to enhance the immunogenicity. The vaccine was administered in mice and rabbits divided into two group each. Phage lysate vaccine (PL-VacI) was administered to group I mice and rabbits whereas group II mice and rabbits received alum precipitated HS vaccine (HS-VacII). Antibody titres were monitored 0, 30, 60, 90, 210 and 240 dpv. An IROMP (130 kDa) based indirect ELISA was also developed to differentiate between infected and vaccinated animals. The Pasteurella phage isolated in present study was sequenced at Georgia Genomic Facilty, Georgia.

RESULT

The sequence of PMP-GAD-IND (Pasteurella bacteriophage) was deposited in GenBank under no KY203335. The group I mice and rabbits vaccinated with Phage lysate vaccine (PL-VacI) group revealed significantly higher antibody titres than group II mice and rabbits receiving alum-precipitated bacterin (HS-VacII) by MAT, IHA and ELISA (P < 0.05 and P < 0.001). The peak log ₁₀ values (3.46) in case of group I mice by ELISA were attained at 90DPI whereas in group II mice the peak values at 90DPI were 2.82. Mean log₁₀ titres by ELISA in group I and II rabbits were 2.43 and 2.35 respectively at 30DPI whereas at 120DPI the titres were 3.29 and 2.75, respectively. The DIVA ELISA detected presence of a novel 137 kDa IROMP/siderophore antibody in sera of group I mice and rabbits (PL-VacI) absent in sera of mice and rabbits given HS-VacII.

CONCLUSION

The bacteriophage based marker vaccine (PL-VacI) had a more effective and longer immune response against HS in mice and rabbit in comparison to the widely used alum precipitated HS vaccine (HS-VacII). Moreover, the development of a recombinant IROMP based indirect ELISA could serve as an excellent tool to differentiate between infected and vaccinated cattle and buffaloes for effective control of HS.

Pasteurella multocida: from zoonosis to cellular microbiology

In a world where most emerging and reemerging infectious diseases are zoonotic in nature and our contacts with both domestic and wild animals abound, there is growing awareness of the potential for human acquisition of animal diseases. Like other Pasteurellaceae, Pasteurella species are highly prevalent among animal populations, where they are often found as part of the normal microbiota of the oral, nasopharyngeal, and upper respiratory tracts. Many Pasteurella species are opportunistic pathogens that can cause endemic disease and are associated increasingly with epizootic outbreaks. Zoonotic transmission to humans usually occurs through animal bites or contact with nasal secretions, with P. multocida being the most prevalent isolate observed in human infections. Here we review recent comparative genomics and molecular pathogenesis studies that have advanced our understanding of the multiple virulence mechanisms employed by Pasteurella species to establish acute and chronic infections. We also summarize efforts being explored to enhance our ability to rapidly and accurately identify and distinguish among clinical isolates and to control pasteurellosis by improved development of new vaccines and treatment regimens.

Profiling of virulence associated genes of Pasteurella multocida isolated from cattle

Pasteurella multocida is a causative agent of many major diseases of which haemorrhagic septiciemia (HS) in cattle & a buffalo is responsible for significant losses to livestock sector in India and south Asia. The disease outcome is affected by various host- and pathogen-specific determinants. Several bacterial species-specific putative virulence factors including the capsular and virulence associated genes have been proposed to play a key role in this interaction. A total of 23 isolates of P. multocida were obtained from 335 cases of various clinically healthy and diseased cattle. These isolates were examined for capsule synthesis genes (capA, B, D, E and F) and eleven virulence associated genes (tbpA, pfhA, toxA, hgbB, hgbA, nanH, nanB, sodA, sodC, oma87 and ptfA) by PCR. A total of 19 P. multocida isolates belonging to capsular type B and 4 of capsular type A were isolated. All isolates of capsular type B harboured the virulence associated genes: tbpA, pfhA, hgbA, sodC and nanH, coding for transferrin binding protein, filamentous hemagglutinin, haemoglobin binding protein, superoxide dismutase and neuraminidases, respectively; while isolates belonging to capsular type A also carried tbpA, pfhA, hgbA and nanH genes. Only 50 % of capsular type A isolates contained sodC gene while 100 % of capsular type B isolates had sodC gene. The gene nanB and toxA were absent in all the 23 isolates. In capsular type A isolates, either sodA or sodC gene was present & these genes did not occur concurrently. The presence of virulence associated gene ptfA revealed a positive association with the disease outcome in cattle and could therefore be an important epidemiological marker gene for characterizing P. multocida isolates.

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.

Mucosal immunization provides better protection than subcutaneous immunization against Pasteurella multocida (B:2) in mice preimmunized with the outer membrane proteins

To investigate the effect of boosting immunity via mucosal route vis-a-vis parenteral route in the mouse model of haemorrhagic septicaemia, mice preimmunized with OMP of Pasteurella multocida (B:2) were immunized with 10(2) cfu of P. multocida via intranasal and subcutaneous routes. Mice were challenged through intranasal route (natural route of infection) with 10(8) cfu 14 days after immunization. Group of mice which were immunized intranasally showed significant protection (P < 0.05) of 88% as compared to 50% protection in group of mice immunized subcutaneously. In the control group of mice, 100% mortality occurred within 48 h. of challenge. The results of present study indicated that boosting of immunity via mucosal route in mice preimmunized with OMP provided better protection against P. multocida. This study may have implications for developing better vaccination strategies for the natural host.

Molecular heterogeneity of plpE gene in Indian isolates of Pasteurella multocida and expression of recombinant PlpE in vaccine strain of P. multocida serotype B: 2

Outer membrane proteins of Pasteurella (P.) multocida have been known to be protective immunogens. Pasteurella lipoprotein E (PlpE) has been reported to be an important cross reactive outer membrane protein in P. multocida. The gene encoding the PlpE of P. multocida serotypes A: 3, B: 2 and D: 1 was amplified from the genomic DNA. The amplified products were cloned and the nucleotide sequence was determined. Sequence analysis of the recombinant clones revealed a single open reading frame of 1,011 bp, 1,008 bp and 1,017 bp encoding a protein with a calculated molecular mass of 37.829 kDa, 37.389 kDa and 37.965 kDa for serotypes A: 3, B: 2 and D: 1 respectively. The comparison of the plpE sequence in different capsular types revealed a high degree (>90%) of homology. Furthermore, the plpE gene of Haemorhhagic septicaemia causing serotype (B: 2) was expressed in E. coli and recombinant PlpE was strongly immunostained by antiserum against whole cell antigen, indicating that the protein is expressed in vivo.

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.

Pasteurella multocida pathogenesis: 125 years after Pasteur

Pasteurella multocida was first shown to be the causative agent of fowl cholera by Louis Pasteur in 1881. Since then, this Gram-negative bacterium has been identified as the causative agent of many other economically important diseases in a wide range of hosts. The mechanisms by which these bacteria can invade the mucosa, evade innate immunity and cause systemic disease are slowly being elucidated. Key virulence factors identified to date include capsule and lipopolysaccharide. The capsule is clearly involved in bacterial avoidance of phagocytosis and resistance to complement, while complete lipopolysaccharide is critical for bacterial survival in the host. A number of other virulence factors have been identified by both directed and random mutagenesis, including Pasteurella multocida toxin (PMT), putative surface adhesins and iron acquisition proteins. However, it is likely that many key virulence factors are yet to be identified, including those required for initial attachment and invasion of host cells and for persistence in a relatively nutrient poor and hostile environment.

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.

Non-viability of Haemophilus parasuis fur-defective mutants

By complementation of an Escherichia coli fur mutant, the Haemophilus parasuis fur gene has been isolated from a genomic library of this organism. The H. parasuis fur gene is the distal one of a three-gene operon. Two genes placed upstream of the H. parasuis fur open-reading frame encode for a hypothetical protein and a flavodoxin, respectively. Attempts performed to isolate an H. parasuis fur-defective mutant either through manganese-resistance selection or exchange markers were unsuccessful. Likewise, anaerobic growth conditions do not enable the attainment of H. parasuis fur-defective mutants either. Nevertheless, H. parasuis clones carrying a knockout mutation in the chromosomal fur gene by insertion of a KmR cassette were obtained when a stable plasmid, containing an additional copy of the transcriptional unit to which the fur gene belongs, was present. Likewise, the presence of a plasmid in which the H. parasuis fur gene is under the control of the Escherichia coli tac promoter allows for the isolation of fur::Km mutants of this organism. Nonetheless, no fur-defective mutants may be isolated from H. parasuis cells harbouring a stable plasmid in which only the single fur gene is contained. These data clearly indicate that H. parasuis cell viability requires the presence of a wild-type fur gene.

Pasteurella multocida contains multiple immunogenic haemin- and haemoglobin-binding proteins

Iron-dependent outer membrane proteins (IROMPs) play an important role in bacterial pathogenesis and present several attributes of potential vaccine candidates. TBLASTN analysis of the Pasteurella multocida Pm70 genome using the same molecules of other bacterial pathogens as a query identified eight putative haemin and haemoglobin receptors for this organism. Quantitative binding assays have demonstrated that the proteins PM0040, PM0236, PM0741, PM1081, PM1428, PM0592 and HgbA bind both haemin and haemoglobin, whereas PM0576 and PM1282 ORFs only bind either haemoglobin or haemin, respectively. Furthermore, Western blot analysis showed that P. multocida-infected mice generate specific antibodies against PM0040, PM0236, PM0741, PM1081, PM1428, PM0592 and HgbA proteins. Nevertheless, inoculation of mice with any single one of these receptors alone did not protect against P. multocida infection.

fur-independent regulation of the Pasteurella multocida hbpA gene encoding a haemin-binding protein

Treatment of bacterial cultures with chelating agents such as 2,2'-dipyridyl (DPD) induces expression of iron-regulated genes. It is known that in the gamma-Proteobacteria, the Fur protein is the major regulator of genes encoding haem- or haemoglobin-binding proteins. Electrophoretic analysis of outer-membrane proteins of the gamma-proteobacterium Pasteurella multocida has revealed the induction of two proteins of 60 and 40 kDa in DPD-treated cultures in both wild-type and fur-defective strains. These two proteins have the same N-terminal amino acid sequence, which identifies this protein as the product of the PM0592 ORF. Analysis of the sequence of this ORF, which encodes a protein of 60 kDa, revealed the presence of a hexanucleotide (AAAAAA) at which a programmed translational frameshift can occur giving rise to a 40 kDa protein. Analyses conducted in Escherichia coli, using the complete PM0592 ORF and a derivative truncated at the hexanucleotide position, have shown that both polypeptides bind haemin. For this reason, the PM0592 ORF product has been designated HbpA (for haemin-binding protein). Expression studies using both RT-PCR and lacZ fusions, as well as electrophoretic profiles of outer-membrane protein composition, have demonstrated that the hbpA gene is negatively regulated by iron, manganese and haemin through a fur-independent pathway. Despite the fact that serum of mice infected with P. multocida contained antibodies that reacted with both the 60 and 40 kDa products of the hbpA gene, these proteins did not offer protection when used in immunization assays against this micro-organism.

Functional characterization of HgbB, a new hemoglobin binding protein of Pasteurella multocida

The biological function and role in pathogenesis of a Pasteurella multocida A:1 strain hemoglobin binding protein was investigated. The hgbB gene from the P. multocida A:1 strain, VP161, was cloned and characterized. hgbB was 2991 bp in length and encoded a mature length protein of 111 kDa. HgbB was predicted to be an outer membrane protein and shared 68 and 69% similarity to the hemoglobin/hemoglobin-haptoglobin binding protein, HI0712 from Haemophilus influenzae Rd and HgpC, from H. influenzae b, respectively. HgbB exhibited features typical of TonB dependent receptors, including seven conserved regions typical of these proteins, and conserved invariant residues. Escherichia coli expressing recombinant HgbB was found to bind hemoglobin in a solid phase dot blot binding assay. However, when a truncated form of the protein was expressed in E. coli, cells could no longer bind hemoglobin. Insertional inactivation of hgbB did not affect the ability of P. multocida to bind hemoglobin, nor its ability to produce disease in a mouse model. In addition, recombinant HgbB did not confer any protection against homologous or heterologous challenge.

Investigation of media formulations promoting differential antigen expression by Photobacterium damsela ssp. piscicida and recognition by sea bass, Dicentrarchus labrax (L.), immune sera

Photobacterium damsela ssp. piscicida (Phdp) isolates were grown in various bacteriological media, in eukaryotic cell culture media and in the presence of fish cells (resembling some aspects of in vivo growth environments). Bacterial cells, extracellular products (ECPs) and crude capsular polysaccharide were isolated and analysed by electrophoresis and Western blot using sea bass sera. Growth in bacteriological media conserved the synthesis of cell and extracellular components when these were compared with those prepared under near-in vivo growth conditions. In fact, synthesis of a larger range of cell components was induced after growth in bacteriological media. Certain media based on yeast extract and peptones from various sources and a specific salt formulation induced the synthesis of novel cell components at approximately 21.3 and 14 kDa. These antigens were recognized by sea bass sera collected after natural pasteurellosis outbreaks and other sea bass sera raised against live or inactivated Phdp cells. The ECPs of the pathogen were not good immunogens in their soluble form despite various treatments prior to immunization. The results are discussed with respect to vaccine development.

Transcriptional response of Pasteurella multocida to defined iron sources

Pasteurella multocida was grown in iron-free chemically defined medium supplemented with hemoglobin, transferrin, ferritin, and ferric citrate as iron sources. Whole-genome DNA microarrays were used to monitor global gene expression over seven time points after the addition of the defined iron source to the medium. This resulted in a set of data containing over 338,000 gene expression observations. On average, 12% of P. multocida genes were differentially expressed under any single condition. A majority of these genes encoded P. multocida proteins that were involved in either transport and binding or were annotated as hypothetical proteins. Several trends are evident when the data from different iron sources are compared. In general, only two genes (ptsN and sapD) were expressed at elevated levels under all of the conditions tested. The results also show that genes with increased expression in the presence of hemoglobin did not respond to transferrin or ferritin as an iron source. Correspondingly, genes with increased expression in the transferrin and ferritin experiments were expressed at reduced levels when hemoglobin was supplied as the sole iron source. Finally, the data show that genes that were most responsive to the presence of ferric citrate did not follow a trend similar to that of the other iron sources, suggesting that different pathways respond to inorganic or organic sources of iron in P. multocida. Taken together, our results demonstrate that unique subsets of P. multocida genes are expressed in response to different iron sources and that many of these genes have yet to be functionally characterized.

Comparative analysis of the outer membrane protein profiles of isolates of the Pasteurella multocida (B:2) associated with haemorrhagic septicaemia

Outer membrane proteins (OMP) of P. multocida (serotype B:2) field isolates (n = 6) and a vaccine strain (P-52) were extracted by a sarkosyl method and characterized using SDS-PAGE and immunoblotting. About 20 polypeptide bands were observed in the profile of the vaccine strain with MW ranging from 16 to 90 kDa and, based on band thickness and intensity of staining, three polypeptides of MW 31, 33 and 37 kDa were considered to be the major OMPs. The profiles of the field isolates showed minor differences when compared with that of the vaccine strain. The OMP of 33 kDa was only expressed by the vaccine strain. Four field isolates expressed an OMP of 39 kDa, which did not appear in the profiles of the remaining two field isolates and the P-52 strain. Similarly, an OMP of 25 kDa was exclusively seen in the profile of a single isolate. By immunoblotting studies, using anti-P. multocida (P-52) whole-cell hyperimmune serum raised in rabbits as well as buffalo immune sera, it became evident that the polypeptide of 37 kDa was the most antigenic OMP in the profiles of all the isolates, including the P-52 strain. Other polypeptides were either weakly antigenic or visible in the profile of only a few of the isolates. The study thus identified the major OMP of P. multocida (B:2) and suggested that this highly antigenic 37 kDa OMP has potential for further protective and immunodiagnostic studies.

Cloning of 87 kDa outer membrane protein gene of Pasteurella multocida P52

Pasteurella multocida serotype B:2 is the causative agent of haemorrhagic septicaemia, a fatal disease of cattle and buffaloes. Formalin inactivated whole cell bacterin is used to prepare vaccines in India. However, outer membrane proteins (OMPS) of P. multocida were reported to be potential immunogens. The 87-kDa OMP of P. multocida P52, serotype B:2 has been identified as one of the major antigens because this protein reacted with serum of vaccinated animals. The gene omp87, encoding an 87-kDa OMP was amplified and cloned into pBluescript SK(-) vector. This gene was found to localise in a 9.0 kb Hind III fragment of P. multocida genome.

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.

Respiratory diseases of rabbits

Respiratory diseases are second only to gastroenteric diseases in importance in rabbits. Pasteurellosis is the primary respiratory disease affecting domestic rabbits, but other bacteria (e.g., Bordetella broniseptica and Staphylococcus spp) are significant opportunistic pathogens. The primary manifestations are upper respiratory disease (e.g., rhinitis, sinusitis, conjunctivitis, and dacryocystitis). Various antimicrobials are effective for treatment.

Candidate vaccine antigens and genes in Pasteurella multocida

Pasteurella multocida is the causative agent of fowl cholera and other diseases of production animals. Isolates are classified into five groups based on capsular antigens and into 16 serotypes based on LPS antigens. Strains causing fowl cholera are most frequently designated A:1, A:3 or A:4. Whole cell bacterins can provide some degree of protection, but only against the homologous LPS serotype. There is good evidence that cross-protective antigens are expressed only under in vivo conditions. Empirically derived, live, attenuated vaccines can protect against heterologous serotypes, but because the basis for attenuation is undefined, reversion to virulence is not uncommon. Work in our laboratory is aimed at using a variety of approaches to identify potential protective antigens or virulence genes to be used as candidates for attenuating mutations or as the basis for vaccine antigen delivery systems. The gene encoding an outer membrane protein, Oma87, which is a homologue of the D15 protective antigen of Haemophilus influenzae, was cloned and sequenced. Rabbit antiserum prepared against recombinant Oma87 could passively protect mice against infection. Type 4 fimbriae form the basis of vaccines against ovine footrot and bovine keratoconjunctivitis. We have identified type 4 fimbriae on the surface of P. multocida, purified the fimbrial subunit protein, PtfA, and determined its N-terminal amino acid sequence. Subsequent cloning of the ptfA gene and its inactivation will now be used to assess the importance of type 4 fimbriae in virulence. There has long been anecdotal evidence for the importance of capsule in virulence, but unequivocal genetic evidence for such a role is lacking. We have cloned and characterised the capsule biosynthetic locus in P. multocida A:1 and identified four bex genes involved in capsule transport and genes encoding enzymes involved in the biosynthesis and transfer of the N-acetyl glucosamine and glucuronic acid components of the capsule. It has been suggested that the low concentration of available iron in vivo acts as an environmental cue for expression of cross-protective antigens. Accordingly, we have cloned and characterised the gene encoding transferrin binding protein, Tbpl, so that its role in immunity and virulence can be investigated. Although P. multocida is not normally considered haemolytic, we have observed haemolysis under anaerobic conditions. Standard library construction and screening resulted in the identification of the mesA gene which encodes an esterase enzyme resulting in a haemolytic phenotype under anaerobic conditions. Virulence studies with mesA- mutants were performed to assess its role in pathogenesis. Using a promoterless phoA gene vector system, the cloning of proteins homologous to known surface proteins of other species as well as proteins unique to P. multocida, allowing their potential as vaccine components to be assessed.

Immunogenicity of outer membrane protein of Pasteurella multocida in buffalo calves

Outer membrane protein (OMP) from Pasteurella multocida serotype B:2 was extracted and characterized using SDS-PAGE. Ten major polypeptide bands of MW 88 to 25 kDa were observed. Immunoblotting suggested that the polypeptides of MW 44, 37 and 30 kDa were the major immunogens. Buffalo calves vaccinated with the OMP vaccine or a commercial haemorrhagic septicaemia oil adjuvant vaccine developed highest mean log10 ELISA titres day 21 postvaccination (pv). Antibody titres detectable in these animals using an indirect haemagglutination assay were lower than the ELISA titres but the pattern of the antibody response was similar. A passive mouse protection assay revealed that the maximum protection against the challenge infection was conferred by the serum collected from both the groups on day 21 pv and 26 pv. Following challenge with virulent P. multocida cells, all the five OMP vaccinated animals survived whereas only 2 out of the 3 HS oil adjuvant vaccinated animals withstood the challenge. Results suggested that OMP was protective and could be used in vaccines against haemorrhagic septicaemia.

Cloning, sequencing, expression, and protective capacity of the oma87 gene encoding the Pasteurella multocida 87-kilodalton outer membrane antigen

Membrane proteins of Pasteurella multocida have been shown previously to elicit protective immunity. We have identified an 87-kDa outer membrane antigen, Oma87, which is present in all 16 serotypes of P. multocida. The gene encoding this protein was cloned and sequenced and found to have significant similarity to the D15 protective surface antigen of Haemophilus influenzae. Oma87 was localized to the outer membrane of the cell, and proteinase K treatment suggested that the protein is surface exposed. Native and recombinant Oma87 were strongly immunostained by convalescent-phase antiserum, indicating that the protein is expressed in vivo. Specific Oma87 antiserum protected mice against homologous, lethal P. multocida challenge. These results suggest that Oma87 is a protective outer membrane antigen of P. multocida.

Immunity and vaccine development in Pasteurella multocida infections

The role of LPS in immunity was studied using monoclonal antibodies (MAbs) and active immunisation experiments. A panel of six MAbs produced against Pasteurella multocida serotype B:2 reacted with the LPS of serotypes B:2 and B:5, but not with other serotypes. The MAbs could opsonise P. multocida for phagocytosis by mouse macrophages, but were not bactericidal in the presence of complement. They conferred only partial passive protection in mice. Similar results showing only partial protection were obtained when purified LPS was used to actively immunise mice prior to challenge, suggesting that LPS plays a partial role in immunity to infection. The aroA gene from P. multocida serotypes A:1 and A:3 was cloned and inactivated by insertion of a kanamycin resistance gene. The mutated gene was re-introduced onto the chromosome by allelic exchange. The resultant aroA mutants were highly attenuated in a mouse model system, with a 6-log decrease in ID50. Virulence could be restored by complementation with a functional aroA gene. Mice immunised with two doses of the live mutants were protected against lethal challenge with the homologous parental strain, but not against the heterologous strain. P. multocida A:1 and A:3 expressed unique proteins when grown in iron-restricted medium. Moreover, the outer membrane (OM) fractions of these cells contained novel proteins of 75 kDa, 85 kDa and 94 kDa molecular mass. Mice were immunised with OM fractions prepared from serotype A:3 grown in iron-restricted (OM Fe-) or iron-replete (OM Fe+) media. When low challenge doses were used, both immunogens protected mice against serotype A:3, but only the OM Fe- fraction protected mice against heterologous challenge with serotype A:1. When higher challenge doses were used, only partial protection was observed.

Serum antibody responses of cattle to iron-regulated outer membrane proteins of Pasteurella haemolytica A1

Serum antibody responses to the 70, 77, and 100 kDa iron-regulated outer membrane proteins (IROMPs) of Pasteurella haemolytica A1 were studied in cattle vaccinated with outer membrane protein (OMP) enriched outer membrane fraction, IROMP-enriched outer membrane fraction or live P. haemolytica. Vaccination with an IROMP-enriched outer membrane fraction stimulated antibodies to the 70 kDa IROMP, whereas vaccination with live P. haemolytica stimulated antibodies to the 70 and 77 kDa IROMPs. In a second experiment, sera were used from cattle vaccinated with live or killed P. haemolytica and subsequently challenged. Significant antibody responses to OMP- and IROMP-enriched outer membrane fractions were detected by an enzyme-linked immunosorbent assay (ELISA) for cattle vaccinated with bacterins or live P. haemolytica. Regression analysis indicated significant correlations between high antibody responses to the OMP- or IROMP-enriched fraction and resistance to challenge. Antibody responses to the 70 and 77 kDa IROMPs were significantly greater for the live P. haemolytica vaccinates than for PBS control vaccinates. There was no significant correlation between antibody responses to individual IROMPs and resistance or susceptibility to challenge. These data suggest that antibodies to IROMPs alone are probably not responsible for protective immunity against pneumonic pasteurellosis. Antibodies to IROMPs, however, in conjunction with antibodies to other surface antigens probably enhance immunity to P. haemolytica challenge.

Pasteurella multocida produces a protein with homology to the P6 outer membrane protein of Haemophilus influenzae

An antibody specific for a 16-kDa outer membrane protein of a rabbit strain of Pasteurella multocida was used to probe representatives of all 16 somatic serotypes of P. multocida, as well as the vaccine strains CU and M9, and all were shown to express the protein. The gene encoding this protein was cloned and sequenced and found to have extensive sequence homology with the gene encoding the P6 protein of Haemophilus influenzae. The protein in P. multocida has been designated P6-like. The gene encoding the P6-like protein was used to probe members of the family Pasteurellaceae and other gram-negative bacteria. Representatives of all 16 somatic serotypes (as well as the vaccine strains CU and M9) of P. multocida hybridized with the P6-like gene under conditions of high stringency. The DNA from H. influenzae hybridized weakly with the P6-like gene under these conditions, but Pasteurella haemolytica (representatives of A and T biotypes), Bordetella bronchiseptica, B. avium, Actinobacillus suis, A. suis-like, A. lignieresii, A. ureae, A. rossii, A. pleuropneumoniae, A. equuli, and various members of the family Enterobacteriaceae (Escherichia coli, Klebsiella pneumoniae, and Salmonella typhimurium) did not hybridize detectably. Under conditions of lower stringency, the P6-like gene also hybridized strongly with DNA from P. multocida, H. influenzae, and A. rossii but weakly with DNA from P. haemolytica and members of the genus Actinobacillus. These results suggest that the P6-like protein of P. multocida might be useful as an immunizing product to protect poultry from avian cholera. This suggestion stems from (i) our finding that the P6-like protein in P. multocida is widely distributed among all the somatic serotypes and (ii) the previous work of others demonstrating that the P6 protein of H. influenzae elicits a protective immune response in animal models of human disease.

Iron uptake by Pasteurella piscicida and its role in pathogenicity for fish

We evaluated the iron uptake mechanisms in Pasteurella piscicida strains as well as the effect of iron overload on the virulence of these strains for fish. With this aim, the capacity of the strains to obtain iron from transferrin and heme compounds as well as their ability to overcome the inhibitory activity of fish serum was analyzed. All the P. piscicida strains grew in the presence of the iron chelator ethylene-diamine-di (O-hydroxyphenyl acetic acid) or of human transferrin, which was used by a siderophore-mediated mechanism. The chemical tests and cross-feeding assays showed that P. piscicida produced a siderophore which was neither a phenolate nor a hydroxamate. Cross-feeding assays as well as preliminary chromatographic analysis suggest that this siderophore may be chemically related to multocidin. All the P. piscicida isolates utilized hemin and hemoglobin as an iron source, since the virulence of the strains increased when the fish were preinoculated with these compounds. This effect was stronger in the avirulent strains (50% lethal dose was reduced by 4 logs when fish were pretreated with hemin or hemoglobin). Only the pathogenic P. piscicida isolates were resistant to the bactericidal action of the fresh fish serum. The nonpathogenic strains grew in fish serum only when it was heat-inactivated or when it was supplemented with ferric ammonium citrate, hemin, or hemoglobin. In all the strains, at least three iron-regulated outer membrane proteins (IROMPs) (105, 118, and 145 kDa) were increased when the strains were cultured in iron-restricted medium.(ABSTRACT TRUNCATED AT 250 WORDS)

[The influence of cations on the letality and on the formation of the toxin of Pasteurella multocida]

The stability of the Pasteurella multocida toxin has proven as very pH dependent. Therefore, a pH lower than 6 should be avoided. A concentration of 1 mM Cu2+ decreased the lethal effect of the toxin but the equimolecular addition of chelators compensated this effect. Possible structure-effect mechanisms were discussed. Iron supplement (100 microM) to two culture media examined did not influence the production of the toxin but during the cultivation in the low-iron medium TDHM the toxin level increased. This increased toxin production was not due to a more intensive multiplication of bacteria.

Binding of bovine transferrin by Pasteurella multocida serotype B:2,5, a strain which causes haemorrhagic septicaemia in buffalo and cattle

Pasteurella multocida serotype B:2,5, which causes haemorrhagic septicaemia in buffalo and cattle, was examined for the presence of transferrin-binding proteins. An 82-kDa iron-regulated outer membrane protein was found which specifically binds bovine transferrin. In contrast, P. multocida serotype B:3,4, associated with haemorrhagic septicaemia in feral ruminants, did not express transferrin-binding proteins. These results might indicate a role for transferrin binding in the pathogenesis of haemorrhagic septicaemia in cattle and buffalo.

Immunogens of Pasteurella

The family Pasteurellaceae Pohl contains Gram-negative, facultatively anaerobic and fermentative bacteria of the genera Pasteurella, Haemophilus, and Actinobacillus. Approximately 20 different species of the genus Pasteurella have been identified using phenotypic and genetic analyses. Of these species, P. multocida and P. haemolytica are the most prominent pathogens in domestic animals causing severe diseases and major economic losses in the cattle, swine, sheep, and poultry industries. Mechanisms of immunity to these bacteria have been difficult to determine, and efficacious vaccines have been a challenge to develop and evaluate. Pasteurella multocida of serogroups A and D are mainly responsible for disease in North American poultry and pigs and to a lesser extent in cattle. Fowl cholera in chickens and turkeys is caused by various serotypes of P. multocida serogroup A and characterized by acute septicemia and fibrinous pneumonia or chronic fibrinopurulent inflammation of various tissues. Current biologicals in use are live P. multocida vaccines and bacterins. Potency tests for avian P. multocida biologicals are a bacterial colony count for vaccines and vaccination and challenge of birds for bacterins. Somatic antigens, particularly lipopolysaccharide (LPS), appear to be of major importance in immunity. In North American cattle, P. multocida serogroup A is associated mainly with bronchopneumonia (enzootic pneumonia) in young calves; however, it is occasionally isolated from fibrinous pleuropneumonia of feedlot cattle (shipping fever). Biologicals currently available are modified-live vaccines and bacterins. The potency test for vaccines is bacterial colony counts. The test for bacterin potency is vaccination and challenge of mice. Important immunogens have not been well characterized for P. multocida infection in cattle. In swine, P. multocida infection is sometimes associated with pneumonia; however, its major importance is in atrophic rhinitis. A protein toxin (dermonecrotic toxin), produced by toxigenic strains of P. multocida types A and D, and concurrent infection with Bordetella bronchiseptica appear to be the major factors in development of atrophic rhinitis. Currently available biologicals are bacterins and inactivated toxins (toxoids). The toxin appears to be the major immunogen for preventing atrophic rhinitis. There are, however, no standardized requirements for potency testing of P. multocida type D toxoid. Various serotypes of P. haemolytica biotype A are responsible for severe fibrinous pleuropneumonia of cattle and sheep, occasionally septicemia of lambs, and mastitis in ewes. Several serotypes of P. haemolytica biotype T are isolated from acute septicemia of lambs. The currently available P. haemolytica biologicals are modified-live vaccines, bacterins, bacterial surface extracts, and culture supernates that contain an exotoxin (leukotoxin).(ABSTRACT TRUNCATED AT 400 WORDS)

Virulence of capsulated and noncapsulated isolates of Pasteurella multocida and their adherence to porcine respiratory tract cells and mucus

The virulence and the adherence to porcine respiratory tract cells and mucus of three toxigenic, capsular type D Pasteurella multocida isolates and their noncapsulated variants were evaluated in the present study. Loss of capsule by P. multocida, verified by transmission electron microscopy after polycationic ferritin labeling, was associated with a massive reduction in virulence of the organisms in mice. Specific-pathogen-free piglets inoculated intranasally with one of the capsulated isolates or its noncapsulated variant developed turbinate lesions characterized by bone resorption and by an inflammation of the mucosa associated with hyperplasia and squamous metaplasia of the epithelium. Infection with the capsulated isolate led to more severe lesions and atrophy of turbinates. The interactions of these P. multocida isolates with porcine respiratory tract cells and mucus were studied in vitro. The presence of capsule resulted in a decrease in binding of respiratory tract mucus were studied in vitro. The presence of capsule resulted in a decrease in binding of respiratory tract mucus to P. multocida isolates as determined by a dot blot assay. The presence of capsule also resulted in a significant decrease in adherence to porcine tracheal rings maintained in culture. The capsule seemed to mask outer membrane components which are involved in adherence. One of these components might be lipopolysaccharide since purified lipopolysaccharide bound respiratory tract mucus and blocked adherence of this microorganism to porcine tracheal rings. Our data indicate that capsular material does not seem to be involved in adherence of P. multocida to respiratory tract cells and mucus, but capsulated isolates are more virulent in mice and also in piglets.

Effects of sub-MICs of antibiotics on cell surface characteristics and virulence of Pasteurella multocida

The effects of sub-MICs of certain antibiotics, namely, penicillin G, tetracycline, and trimethoprim-sulfamethoxazole, on the cell surface characteristics and the virulences of two toxigenic isolates of Pasteurella multocida representing capsular types A and D were evaluated. Expression of proteins, in particular, outer membrane proteins and iron-regulated proteins, was not affected by exposure of bacterial cells to low concentrations of antibiotics. However, exposition of surface antigens was modified by sub-MICs of the antibiotics tested. The lipopolysaccharide profile of one isolate (capsular type D) was altered by penicillin G. Sub-MICs of penicillin G and tetracycline diminished the virulence of the capsular type A isolate and adherence to porcine tracheal rings of the capsular type D isolate. Production of dermonecrotic toxin was not affected by sub-MICs of the antibiotics tested. Our results indicate that growth of P. multocida in the presence of low concentrations of antibiotics seems to have, depending on the isolate, profound effects on cell surface characteristics, with concomitant effects on adherence or virulence. Our results also indicate that production of dermonecrotic toxin, an important virulence factor of P. multocida isolates associated with porcine atrophic rhinitis, was not affected by sub-MICs of the antibiotics studied.