Recombinant derivatives of Pasteurella multocida toxin: candidates for a vaccine against progressive atrophic rhinitis

Method for quantifying the Pasteurella multocida antigen adsorbed on aluminum hydroxide adjuvant in swine atrophic rhinitis vaccine

Swine atrophic rhinitis is a disease caused by Pasteurella multocida and Bordetella bronchiseptica that affects pigs. Inactivated vaccines containing the toxins produced by Pasteurella multocida and Bordetella bronchiseptica have been widely used for the prevention of swine atrophic rhinitis. The efficacy of a vaccine is correlated with the amount of antigen present; however, the protective toxin of P. multocida bound to aluminum hydroxide, which is used as an adjuvant, can hinder the monitoring of the antigen concentration in the vaccine. This study assessed the applicability of a dot immunoassay as an antigen quantification method using monoclonal antibodies. This quantification method was able to detect the antigen with high specificity and sensitivity even when the antigen was bound to the adjuvant, and its application to vaccine products revealed a correlation between the amount of antigen present in the vaccine and the neutralizing antibody titers induced in pigs. The antigen quantification method presented in this study is a simple and sensitive assay capable of quantifying the amount of antigen present in a vaccine that can be used as an alternative quality control measure.

Cross-protection of recombinant Pasteurella multocida toxin proteins against atrophic rhinitis in mice

Pasteurella multocida (P. multocida) infects the swine respiratory tract and mainly causes atrophic rhinitis (AR). Recently, many commercially inactivated and subunit vaccines have been used as preventive strategies. However, the best antigenic protein portion has not been selected, and the aluminum gel was used as the adjuvant, which may not induce full protection. P. multocida toxin (PMT) is the major virulence factor responsible for AR. PMT is a monomeric 146 kDa protein (approximately 1285 amino acids) encoded by the tox A gene. In this study, we expressed different fragments of recombinant PMT proteins, combined them with a water-in-oil-in-water adjuvant, and evaluated mice's immune response. The results indicated that the rPMT-C-immunized group showed significantly higher levels (p < 0.05) of IgG, IgG2a antibody and interferon-γ, IL-12 cytokine expression than other groups. Furthermore, vaccination with rPMT-C recombinant protein can provide homologous and heterologous protection against P. multocida challenge. In conclusion, our approach may be feasible for developing an effective subunit vaccine against atrophic rhinitis with a cost-down simple ingredient.

Variability of Pasteurella multocida isolated from Icelandic sheep and detection of the toxA gene

Pasteurella multocida can be part of the upper respiratory flora of animals, but under conditions of stress or immunocompromisation, the bacteria can cause severe respiratory symptoms. In this study, we compared 10 P. multocida isolates from Icelandic sheep with respiratory symptoms and 19 isolates from apparently healthy abattoir sheep. We examined capsule type, genetic variability and the presence of the toxA gene in the two groups. Surprisingly, we found that all ovine P. multocida isolates examined in this study carried the toxA gene, which markedly differs from what has been published from other studies. Interestingly, all isolates from abattoir animals were capsule type D, whilst bacteria isolated from animals with clinical respiratory symptoms had capsule type A, D or F. Examination of seven housekeeping genes indicated that the clinical respiratory isolates were significantly more heterogeneous than the abattoir isolates (P<0.05, two-tailed Mann-Whitney U test). The results suggest that there may be at least two groups of P. multocida in sheep - a genetically homogeneous group that resides in the respiratory tract and a genetically heterogeneous group that is the predominant cause of disease.

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.

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.

Protective immunity conferred by the C-terminal fragment of recombinant Pasteurella multocida toxin

Pasteurella multocida serogroup D, producing P. multocida toxin (PMT), is a causative pathogen of progressive atrophic rhinitis (PAR) in swine. To evaluate the protective immunity and vaccination efficacy of the truncated form of PMT, a C-terminal form of recombinant PMT (designated PMT2.3; amino acid residues 505 to 1285 of PMT) was expressed in an Escherichia coli expression system, and the humoral and cellular immune responses to PMT2.3 were investigated. PMT2.3 vaccination in mice led to high levels of the anti-PMT antibody with a high neutralizing antibody titer. PMT2.3 also induced a cellular immune response to PMT, as demonstrated by the lymphocyte proliferation assay. Furthermore, strong protection against a homologous challenge with P. multocida was also observed in mice vaccinated with PMT2.3. In PMT2.3 vaccination in swine, high levels of serum antibody titers were observed in offspring from sows vaccinated with PMT2.3. Offspring from sows vaccinated with PMT2.3 or toxoid showed a good growth performance as depicted by mean body weight at the time of sacrifice, as well as in average daily gain in the postweaning period. Low levels of pathological lesions in turbinate atrophy and pneumonia were also observed in these offspring. Therefore, we consider PMT2.3--in the truncated and nontoxic recombinant PMT form--to be an attractive candidate for a subunit vaccine against PAR induced by P. multocida infection.

Efficacy of a novel Pasteurella multocida vaccine against progressive atrophic rhinitis of swine

The efficacy of a novel vaccine composed of three short recombinant subunit Pasteurella multocida toxin (PMT) proteins in combination with a bi-valent P. multocida whole-cell bacterin (rsPMT-PM) was evaluated in field studies for prevention and control of progressive atrophic rhinitis (PAR) of swine at 15 conventional farrow-to-finish farms. Experimental piglets that were immunized twice with the rsPMT-PM vaccine developed detectable titers of neutralizing antibodies (greater than 1:8) that prevented the growth retardation and pathological lesions typically observed following challenge with authentic PMT. A total of 542 sows were vaccinated once or twice prior to parturition and serum neutralizing antibody titers were evaluated. Both single and double vaccination protocols induced neutralizing antibody titers of 1:16 or higher in 62% and 74% of sows, respectively. Notably, neither sows nor piglets at a farm experiencing a severe outbreak of PAR at the time of the vaccination trial had detectable antibody titers, but antibody titers increased significantly to 1:16 or higher in 40% of sows following double vaccination. During the year after vaccination, clinical signs of PAR decreased in fattening pigs and growth performance improved sufficiently to reduce the rearing period until marketing by 2 weeks. Collectively, these results indicate that the rsPMT-PM vaccine could be used to provide protective immunity for controlling the prevalence and severity of PAR among farm-raised swine.

Veterinary vaccine development from an industrial perspective

Veterinary vaccines currently available in Europe and in other parts of the world are developed by the veterinary pharmaceutical industry. The development of a vaccine for veterinary use is an economic endeavour that takes many years. There are many obstacles along the path to the successful development and launch of a vaccine. The industrial development of a vaccine for veterinary use usually starts after the proof of concept that is based on robust academic research. A vaccine can only be made available to the veterinary community once marketing authorisation has been granted by the veterinary authorities. This review gives a brief description of the regulatory requirements which have to be fulfilled before a vaccine can be admitted to the market. Vaccines have to be produced in a quality controlled environment to guarantee delivery of a product of consistent quality with well defined animal and consumer safety and efficacy characteristics. The regulatory and manufacturing legislative framework in which the development takes place is described, as well as the trend in developments in production systems. Recent developments in bacterial, viral and parasite vaccine research and development are also addressed and the development of novel adjuvants that use the expanding knowledge of immunology and disease pathology are described.

Application of intact cell-based NFAT-beta-lactamase reporter assay for Pasteurella multocida toxin-mediated activation of calcium signaling pathway

Pasteurella multocida toxin (PMT) stimulates and subsequently uncouples phospholipase C beta1 (PLCbeta1) signal transduction through its selective action on the alpha subunit of the Gq-protein. Here, we describe the application of an NFAT-beta-lactamase reporter assay as a functional readout for PMT-induced activation of the Gq-protein-coupled PLCbeta1-IP(3)-Ca(2+) signaling pathway. Use of the NFAT-beta-lactamase reporter assay with a cell-permeable fluorogenic substrate provides high sensitivity due to the absence of endogenous beta-lactamase activity in mammalian cells. This assay system was optimized for cell density, dose and time exposure of PMT stimulation. It is suited for quantitative characterization of PMT activity in mammalian cells and for use as a high-throughput screening method for PMT deletion and point mutants suitable for vaccine development. This method has application's for diagnostic screening of clinical isolates of toxinogenic P. multocida.

Immune response in mice and swine to DNA vaccines derived from the Pasteurella multocida toxin gene

DNA vaccines were constructed with either a 5'-truncated or full-length, genetically detoxified toxin gene from Pasteurella multocida and two different DNA vaccine vectors, distinguished by the presence or absence of a secretion signal sequence. Optimal PMT-specific antibody responses and spleen cell secretion of interferon-gamma following immunization of mice were achieved with pMM4, the construct containing a signal sequence and encoding the entire toxin. Antibody responses were also induced in pigs immunized with pMM4 and levels increased significantly following booster injections and experimental infection with P. multocida. Significantly increased expression of interferon-gamma was detected in only a small subset of pMM4-immunized pigs. This report documents, for the first time, the ability of a DNA vaccine to elicit immune responses to the P. multocida toxin in both mice and swine.

Analytical verification of a multiplex PCR for identification of Bordetella bronchiseptica and Pasteurella multocida from swine

Bordetella bronchiseptica and Pasteurella multocida are etiologic agents of progressive atrophic rhinitis (PAR) and bronchopneumonia in swine. Only dermonecrotic toxin-producing strains of P. multocida play a role in atrophic rhinitis while both toxigenic and nontoxigenic strains have been associated with pneumonia. Monitoring and investigation of outbreaks involving these bacteria require sensitive and accurate identification and reliable determination of the toxigenic status of P. multocida isolates. In the present study, we report the development, optimization, and performance characteristics of a multiplex PCR assay for simultaneous amplification of up to three different targets, one common to all P. multocida strains, one found only in toxigenic P. multocida strains, and one common to B. bronchiseptica strains. Based on analysis of 94 P. multocida isolates (31 toxigenic) and 126 B. bronchiseptica isolates assay sensitivity is 100% for all amplicons. Evaluation of 22 isolates of other bacterial genera and species commonly found in the swine respiratory tract demonstrated a specificity of 100% for all gene targets. The limit of detection for simultaneous amplification of all targets is 1-10pg of DNA per target, corresponding to a few hundred genomes or less. Amplicon mobility in agarose gels and sequence analysis indicate the amplicons are highly stable. The data presented establish this multiplex PCR as a reliable method for identification of B. bronchiseptica and both toxigenic and nontoxigenic P. multocida that may greatly simplify investigations of swine PAR and bronchopneumonia.

Immunogenicity and efficacy of three recombinant subunit Pasteurella multocida toxin vaccines against progressive atrophic rhinitis in pigs

Three short fragments of recombinant subunit Pasteurella multocida toxin (rsPMT) were constructed for evaluation as candidate vaccines against progressive atrophic rhinitis (PAR) of swine. PMT-specific antibody secreting cells and evidence of cellular immunity were detected in rsPMT-immunized pigs following authentic PMT challenge or homologous antigen booster. Piglets immunized with rsPMT fragments containing either the N-terminal or the C-terminal portions of PMT developed high titers of neutralizing antibodies. Pregnant sows immunized with rsPMT had higher levels of maternal antibodies in their colostrum than did those immunized with a conventional PAR-toxoid vaccine. Offspring from rsPMT vaccinated sows had better survival after challenge with a five-fold lethal dose of authentic PMT and had better growth performance after challenge with a sublethal dose of toxin. Our findings indicate these non-toxic rsPMT proteins are attractive candidates for development of a subunit vaccine against PAR in pigs.

Development of a genetically modified nontoxigenic Pasteurella multocida toxin as a candidate for use in vaccines against progressive atrophic rhinitis in pigs

OBJECTIVE

To construct a genetically modified nontoxigenic Pasteurella multocida toxin (PMT) and examine its immunoprotective activity against challenge exposure with wild-type PMT in pigs.

ANIMALS

5 healthy pigs.

PROCEDURE

A nontoxigenic PMT was created by replacing the serine at position 1164 with alanine (S1164A) and the cysteine at position 1165 with serine (C1165S). Toxic activity was determined by use of the guinea pig skin test and mouse lethality test. Three pigs were vaccinated twice with the modified PMT, and the remaining 2 pigs served as nonvaccinated control animals. Vaccinated and control pigs were challenge exposed with wild-type PMT. Pigs were euthanatized and necropsied on day 14 after challenge exposure. Turbinate atrophy was examined macroscopically and assigned a score. Serum anti-PMT antibodies were determined by use of an ELISA.

RESULTS

The genetically modified PMT was characterized by a total lack of toxic activity. Pigs vaccinated with the modified PMT became seropositive; in contrast, control pigs remained seronegative. Necropsy revealed that the 2 control pigs had moderate and severe turbinate atrophy, respectively, whereas the 3 vaccinated pigs did not have any lesions in the turbinates or abnormalities in other organs.

CONCLUSIONS AND CLINICAL RELEVANCE

Modification by use of S1164A and C1165S leads to a complete loss of toxic effects of PMT without impairment of the ability to induce protective immunity in pigs. Analysis of these results suggests that genetically modified PMT may represent a good candidate for use in developing a vaccine against progressive atrophic rhinitis in pigs.

Protective effect of Pasteurella multocida cell-free antigen and toxoid against challenge with toxigenic strains of pasteurella multocida in mice

The cell-free antigen (CFA) obtained from the culture supernatant of Pasteurella multocida (P. multocida) and the toxin (PMT) purified from CFA were inactivated and mixed with oil adjuvant to prepare a trial vaccine. Both of the mice immunized with CFA and PMT toxoid vaccine were noticeably protected against intratracheal challenge with toxigenic strains of P. multocida. Nevertheless, the protective indices of the mice immunized with CFA vaccine indicate that it is more protective and clears away the bacteria more promptly than in the mice immunized with PMT vaccine. The results suggested that CFA would possibly be good as an effective antigen to toxigenic strains of P. multocida infection.

Protection of piglets against atrophic rhinitis by vaccinating the sow with a vaccine against Pasteurella multocida and Bordetella bronchiseptica

The efficacy of a new vaccine against atrophic rhinitis in pigs was tested in the Netherlands and Denmark. The vaccine contained protein dO (a truncated Pasteurella multocida toxin which is immunogenic and non-toxic), inactivated Bordetella bronchiseptica whole cells, and an adjuvant. The sows were either vaccinated intramuscularly with 2 ml of the vaccine at six to eight and two to four weeks before expected farrowing or left unvaccinated as controls. All the piglets were challenged intranasally with B bronchiseptica when three to seven days old and with P multocida three to four days later. Pigs born to the vaccinated sows performed significantly better than pigs born to the control sows when judged on growth, average daily weight gain and snout scores. The challenge organisms were reisolated more frequently from the control pigs than from the pigs in the vaccinated group. The vaccinated sows and their progeny developed high titres of antibodies against B bronchiseptica and P multocida toxin.

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

We have previously shown that a Pasteurella multocida cexA mutant (PBA875) was impaired in capsule export and highly attenuated in virulence for mice (J. D. Boyce and B. Adler, Infect. Immun. 68:3463-3468, 2000). In this study we show that immunization with high, but not low, doses of PBA875 can confer significant protection against wild-type challenge. We have also constructed a genetically defined acapsular P. multocida strain (AL18) by inactivation of bcbH, a gene predicted to be involved in polysaccharide biosynthesis. AL18 failed to produce immunoreactive polysaccharide as determined by immunofluorescence and Western immunoblot. Immunization of mice with live AL18 conferred significant protection against wild-type challenge, while immunization with similar doses of either killed wild-type or killed AL18 failed to confer protection.

The molecular biology of pasteurella multocida

Pasteurella multocida is an important veterinary and opportunistic human pathogen. The species is diverse and complex with respect to antigenic variation, host predeliction and pathogenesis. Certain serological types are the aetiologic agents of severe pasteurellosis, such as fowl cholera in domestic and wild birds, bovine haemorrhagic septicaemia and porcine atrophic rhinitis. The recent application of molecular methods such as the polymerase chain reaction, restriction endonuclease analysis, ribotyping, pulsed-field gel electrophoresis, gene cloning, characterisation and recombinant protein expression, mutagenesis, plasmid and bacteriophage analysis and genomic mapping, have greatly increased our understanding of P. multocida and has provided researchers with a number of molecular tools to study pathogenesis and epidemiology at a molecular level.

Localization of the intracellular activity domain of Pasteurella multocida toxin to the N terminus

We have shown that Pasteurella multocida toxin (PMT) directly causes transient activation of Gqalpha protein that is coupled to phosphatidylinositol-specific phospholipase Cbeta1 in Xenopus oocytes (B. A. Wilson, X. Zhu, M. Ho, and L. Lu, J. Biol. Chem. 272:1268-1275, 1997). We found that antibodies directed against an N-terminal peptide of PMT inhibited the toxin-induced response in Xenopus oocytes, but antibodies against a C-terminal peptide did not. To test whether the intracellular activity domain of PMT is localized to the N terminus, we conducted a deletion mutational analysis of the PMT protein, using the Xenopus oocyte system as a means of screening for toxin activity. Using PCR and conventional cloning techniques, we cloned from a toxinogenic strain of P. multocida the entire toxA gene, encoding the 1,285-amino-acid PMT protein, and expressed the recombinant toxin as a His-tagged fusion protein in Escherichia coli. We subsequently generated a series of N-terminal and C-terminal deletion mutants and expressed the His-tagged PMT fragments in E. coli. These proteins were screened for cytotoxic activity on cultured Vero cells and for intracellular activity in the Xenopus oocyte system. Only the full-length protein without the His tag exhibited activity on Vero cells. The full-length PMT and N-terminal fragments containing the first 500 residues elicited responses in oocytes, but the C-terminal 780 amino acid fragment did not. Our results confirm that the intracellular activity domain of PMT is localized to the N-terminal 500 amino acids of the protein and that the C terminus is required for entry into cells.

Induction of protective immunity in rabbits by coadministration of inactivated Pasteurella multocida toxin and potassium thiocyanate extract

Pasteurella multocida is a bacterial pathogen that causes rhinitis (snuffles), pneumonia, otitis media, septicemia, metritis, and death in domestic rabbits. Currently, there are no effective vaccines to prevent infection by this organism. Subcutaneous (s.c.) immunization with either exotoxin or thiocyanate extracts of P. multocida induces partial protection in rabbits. Since disease begins at mucosal sites, induction of local immunity may be important in preventing systemic disease. Little is known concerning the efficacy of intranasal (i.n. ) administration of these antigens in inducing protective mucosal immunity to P. multocida in rabbits. The purpose of this study was twofold: (i) to investigate the effectiveness of vaccination with purified P. multocida toxin (PMT) and a potassium thiocyanate extract of P. multocida (CN) in combination and (ii) to evaluate the efficacy of administration of these antigens i.n. versus s.c. Forty-eight rabbits were randomly divided into eight different treatment groups. Rabbits received either one or both antigens by either s.c. or i.n. administration. Following vaccination, each group received an i.n. challenge of P. multocida. Rabbits vaccinated with both antigens i.n. or s.c. had a 100% survival rate, few or no bacteria in the liver and lungs, high serum immunoglobulin G (IgG) and IgM antibody titers, and significant numbers of IgG antibody-secreting cells (ASC) in the spleen and tracheobronchial lymph node. Rabbits vaccinated i.n. had significant nasal and bronchoalveolar lavage IgA antibody levels. Rabbits vaccinated with only one antigen, either PMT or CN, had lower antibody titers, moderate to severe liver and lung infections, and fewer ASC compared to rabbits receiving both antigens. Rabbits in the control groups had moderate to severe liver and lung infections. This study indicates that i.n. immunization with both PMT and CN induces an effective response against homologous P. multocida challenge.

Characterization of a Pasteurella multocida plasmid and its use to express recombinant proteins in P. multocida

The complete nucleotide sequence of a naturally occurring 5.36-kb streptomycin and sulphonamide resistance plasmid, designated pIG1, isolated from type D Pasteurella multocida was determined. A 1.6-kb noncoding region and a 1.4-kb region encoding three putative proteins were shown by sequence homologies and functional characterizations to be involved in the replication and mobilization of pIG1, respectively. The remaining sequence carried an unusual arrangement of streptomycin- and sulphonamide-resistant genes when compared to various other plasmids. It appears that the antibiotic resistance region of pIG1 may have evolved by recombination between three different short direct repeat DNA sequences. A 4.5-kb recombinant plasmid was constructed by replacing the antibiotic resistance genes of pIG1 with a kanamycin resistance gene and seven unique restriction sites. The resulting plasmid, designated pIG112, stably replicates in P. multocida, Pasteurella haemolytica, Actinobacillus pleuropneumoniae, and Escherichia coli and can be introduced into these organisms by either transformation or conjugation. This vector exists at approximately 70 copies per cell in P. multocida and approximately 20 copies per cell in E. coli. To demonstrate plasmid-borne gene expression in P. multocida, the P. multocida dermonecrotic toxin gene, toxA, and a genetically modified form of this gene were cloned into pIG112 and expressed in high amounts in a nontoxigenic P. multocida strain. Cell culture assays demonstrated that nontoxigenic P. multocida expressing toxA was cytopathic, whereas a strain expressing the modified toxA derivative was not.

Field trials with a new genetically engineered vaccine for protection against progressive atrophic rhinitis in pigs

Field trials were carried out testing a new genetically engineered vaccine against Progressive Atrophic Rhinitis. The vaccine contained a non-toxic recombinant derivative of the P. multocida toxin. The experimental vaccine was compared with a commercial vaccine in 4 farms and in 1 farm 2 different dose regimens were applied. A total of 825 sows were included. The primary efficacy variable was a comparison of post mortem evaluation of the degree of conchae atrophy in the 4585 pigs. The pigs were slaughtered at normal slaughter weight. The secondary efficacy variables were serological response and age at slaughter. In all farms the experimental vaccine provided significantly better protection of the progeny than the control vaccine. The serological response in sows was significantly higher in all farms than the response to the control vaccine. The serological response did not differ between farms.

Field evaluation of thirteen regimens for the control of progressive atrophic rhinitis

The purpose of the study was to evaluate, under field conditions, the effect of prophylactic programs for the control of progressive atrophic rhinitis (PAR)--recommended in different countries. The investigations were carried out on 280 pregnant sows divided into 14 equal groups and 50 slaughter pigs randomly selected from the litters produced by the sows of each of the groups. Efficacy of all programs was recognized on the basis of comparative evaluation of the average daily gain (ADG), morphometric examination of turbinate bones and computer conchal morphometry (TPR). An increase in ADG was noted in 12 of 13 experimental groups when compared to the control group. Usefulness of the evaluated programs differed significantly. Results of TPR relate only partially to the results of visual morphometry and results of ADG.

Differentiation of toxigenic from nontoxigenic isolates of Pasteurella multocida by PCR

A PCR assay was developed for the differentiation of toxigenic Pasteurella multocida subsp. multocida strains, the major etiologic agent for progressive atrophic rhinitis in pigs, from nontoxigenic strains. The PCR targeted a toxA gene encoding a 143-kDa dermonecrotic toxin that is considered to be the central etiologic factor in progressive atrophic rhinitis. toxA fragments were amplified from toxigenic P. multocida isolates but not from nontoxigenic isolates or other bacteria isolated from pigs. The sensitivity of the reaction was as low as 10 pg of chromosomal DNA from a toxigenic strain. The results obtained by PCR of the DNAs of 187 field isolates of P. multocida were consistent with those obtained by the guinea pig skin test and Western blot (immunoblot) analysis. Restriction fragment analysis of the PCR-amplified fragments from 67 field isolates and comparison of the DNA sequences of fragments from capsular serotype A and D strains suggest that the PCR-amplified region, which is considered to encode the major immunologic determinants of the toxin, would be the same among P. multocida strains. The PCR that we describe should be useful for the diagnosis and the etiologic survey of progressive atrophic rhinitis.

[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.

Field trials with a new genetically engineered vaccine for protection against progressive atrophic rhinitis in pigs

Field trials were carried out testing a new genetically engineered vaccine against Progressive Atrophic Rhinitis. The vaccine contained a non-toxic recombinant derivative of the P. multocida toxin. The experimental vaccine was compared with a commercial vaccine in 4 farms and in 1 farm 2 different dose regimens were applied. A total of 825 sows were included. The primary efficacy variable was a comparison of post mortem evaluation of the degree of conchae atrophy in the 4585 pigs. The pigs were slaughtered at normal slaughter weight. The secondary efficacy variables were serological response and age at slaughter. In all farms the experimental vaccine provided significantly better protection of the progeny than the control vaccine. The serological response in sows was significantly higher in all farms than the response to the control vaccine. The serological response did not differ between farms.

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)

The outer membrane of Pasteurella multocida 3:A protects rabbits against homologous challenge

The protective efficacy of a vaccine purified from the Pasteurella multocida 3:A outer membrane (OM) was evaluated in rabbits by homologous challenge. Twenty-seven rabbits were divided into four groups: 1, vaccinated with OM and challenged; 2, nonvaccinated and challenged; 3, vaccinated with OM only; and 4, nonvaccinated and not challenged. Rabbits were immunized intranasally with 1 mg of OM protein on days 0, 7, 14, and 35, challenged intranasally on day 49, and killed on day 63. Mortality rates were 0, 67, 0, and 0% for groups 1 through 4, respectively. The prevalence of pneumonia was reduced from 73 (group 2) to 20% (group 1). The severity of pneumonia was reduced from 0.62 (group 2) to 0.07 (group 1), as measured by the group lesion index. The number of P. multocida in nasal cavities was reduced from 3.89 x 10(5) (group 2) to 6.19 x 10(2) (group 1). The geometric mean number of P. multocida in lungs was 8,360,000-fold less in group 1 than in group 2. Similarly, the prevalence of P. multocida colonization in nonrespiratory organs was reduced from 47 (group 2) to 4% (group 1). Furthermore, group 1 and 3 rabbits developed significantly elevated immunoglobulin A antibodies in nasal secretions and lung lavages and significantly elevated immunoglobulin G antibodies in lung lavages and sera. In addition, rabbit immune sera contained antibodies against P. multocida OM proteins and lipopolysaccharides and inhibited P. multocida proliferation in mouse lungs. These results indicate that a vaccine prepared from the OM of P. multocida provides a significant protection in rabbits against homologous challenge.

Characterization of the immunogenicity of formaldehyde detoxified Pasteurella multocida toxin

The immunogenicity of the Pasteurella multocida toxin (PMT) was studied in murine model systems. Mice were vaccinated with either formaldehyde treated pure PMT (pure toxoid) or formaldehyde treated crude extract of toxigenic P. multocida (crude toxoid). The corresponding mean anti-PMT titres, sero-conversion rates and survival rates after challenge with affinity purified PMT were compared. When assessed both by anti-PMT titres and seroconversion and challenge, pure toxoid was a more potent immunogen than crude toxoid. This greater immunogenic potency was unaffected by the addition of killed cell preparations of Bordetella bronchiseptica, non-toxigenic P. multocida and B. pertussis. Increasing anti-PMT titres and seroconversion rates were induced by increasing doses of formaldehyde treated PMT (fPMT) in the pure toxoid vaccines, but not in the vaccines containing crude toxoid. However, improved survival rates were observed for both types of vaccine, when the fPMT content was raised. Immunization of pregnant mice with vaccines containing fPMT induced protection of the offspring against challenge with PMT; the protection of the offspring corresponded to that of the mother.