Detection and enumeration of toxin-producing Pasteurella multocida with a colony-blot assay

Regeneration of toxigenic Pasteurella multocida induced severe turbinate atrophy in pigs detected by computed tomography

Background

Atrophic rhinitis is a widely prevalent infectious disease of swine caused by Bordetella bronchiseptica and Pasteurella multocida. The course of the disease is considered to be different depending on the principal aetiological agents distinguishing B. bronchiseptica induced non-progressive and toxigenic P. multocida produced progressive forms. In order to compare the pathological events of the two forms of the disease, the development of nasal lesions has longitudinally been studied in pigs infected by either B. bronchiseptica alone or B. bronchiseptica and toxigenic P. multocida together using computed tomography to visualise the nasal structures.

Results

B. bronchiseptica infection alone caused moderately severe nasal turbinate atrophy and these lesions completely regenerated by the time of slaughter. Unexpectedly, complete regeneration of the bony structures of the nasal cavity was also observed in pigs infected by B. bronchiseptica and toxigenic P. multocida together in spite of seeing severe turbinate atrophy in most of the infected animals around the age of six weeks.

Conclusions

B. bronchiseptica mono-infection has been confirmed to cause only mild to moderate and transient lesions, at least in high health status pigs. Even severe turbinate atrophy induced by B. bronchiseptica and toxigenic P. multocida combined infection is able to be reorganised to their normal anatomical structure. Computed tomography has further been verified to be a useful tool to examine the pathological events of atrophic rhinitis in a longitudinal manner.

Atrophic rhinitis vaccine composition triggers different serological profiles that do not correlate with protection

Atrophic rhinitis (AR) is a widespread and economically important disease of swine caused by Bordetella bronchiseptica and Pasteurella multocida. It can be controlled by vaccination. This study investigates the effect of altering the composition (adjuvants and/or addition of formalin-inactivated P. multocida toxin, fPMT) of conventional vaccines on the serological profile and on protection against AR in swine. A significantly higher B. bronchiseptica specific antibody titre was detected for vaccines with novel immunostimulants, the best being Montanide IMS 1313 (1:630 compared to 1:274 obtained with alum). The highest B. bronchiseptica antibody titre was demonstrated for a combination of B. bronchiseptica--fPMT, while PMT antibody titre was highest for monovalent fPMT (both adjuvanted with IMS 1313). The AR-specific antibodies were transmitted from dams to their offspring in similar titres and with the same hierarchy of effectiveness. After a B. bronchiseptica--P. multocida bacterial challenge, piglets from dams vaccinated with fPMT combined with B. bronchiseptica or B. bronchiseptica--P. multocida bacterins showed the lowest nasal lesions scores (4.5 and 3.2, respectively, out of a possible maximum score of 18). These combinations, both of which were adjuvanted with IMS 1313, gave the best protection against experimentally induced AR. Our results show that the adjuvant and the antigen composition of the vaccine strongly affect seroconversion, and that the AR-specific antibody titre does not necessarily correlate with the degree of protection.

Phenotypic and genotypic characterisation of Pasteurella multocida strains isolated from pigs in Hungary

A total of 146 Pasteurella multocida strains isolated from swine in Hungary in the last 20 years were examined. Biochemical characterisation and PCR-based techniques were used to determine species, subspecies, biovar, capsule type and presence of the toxA gene. Eighty-seven percent of the isolates belonged to P. multocida ssp. multocida, and 98% of these had biovar 3 or were trehalose- or lactose-fermenting or ornithine decarboxylase negative variants of that. Ten percent of the strains were P. multocida ssp. septica, and within this group 80% of the strains showed sorbitol-negative biovars (5, 6 and 7). The rest of the strains (20%) were lactose positive. Only 3% of the porcine isolates were P. multocida ssp. gallicida and 3 out of the 4 strains belonged to the dulcitol-fermenting biovar 8. Using a capsule-specific multiplex PCR, 60% of the strains belonged to capsule type D, 38% to capsule type A, and only 1 isolate had capsule type F. In contrast with data published in the literature, only 3% of capsule type D isolates carried the toxA gene, while this ratio was 41% for the type A strains. A remarkable regional distribution of toxA gene positive strains was observed. All but two isolates were found in swine herds located in the Transdanubian region, separated from other parts of Hungary by the river Danube.

Diagnostic and typing options for investigating diseases associated with Pasteurella multocida

Pasteurella multocida is responsible for major animal diseases of economic significance in both developed and developing countries whereas human infections related to this bacterium are infrequent. Significantly, development of a carrier status or latent infections plays a critical role in the epidemiology of these diseases. Aiming at increased knowledge of these infections, we examine potential diagnostic and selected typing systems for investigating diseases caused by P. multocida. Detection of P. multocida from clinical specimen by; (i) isolation and identification, (ii) polymerase chain reaction (PCR), iii) specific hybridisation probes, (iv) serological tests and (v) other alternative methods is critically evaluated. These detection systems provide a wide spectrum of options for rapid diagnosis and for detecting and understanding of latent infections in herd/flock health control programmes, though PCR methods for detecting P. multocida in clinical specimen appear increasingly preferred. For establishing the clonality of outbreak strains, we select to discuss macromolecular profiling, serotyping, biotyping, restriction enzyme analysis, ribotyping and multiplex PCR typing. Although P. multocida infections can be rapidly diagnosed with molecular and serological tests, isolation and accurate species identification are central to epidemiological tracing of outbreak strains. Our review brings together comprehensive and essential information that may be adapted for confirming diagnosis and determining the molecular epidemiology of diseases associated with P. multocida.

Microfluidic chip analysis of outer membrane proteins responsible for serological cross-reaction between three Gram-negative bacteria: Proteus morganii O34, Escherichia coli O111 and Salmonella Adelaide O35

Bacterial strains have complex and individual antigenic structure, which provides basis for their serological identification. However, serological cross-reaction may occur when antibodies against a certain strain recognize other strains too. The molecular basis of this phenomenon is the expression of similar or identical antigenic epitopes on the surface of different bacterial cells. Such cross-reactions might harden the serological diagnosis of pathogenic bacteria. But it can be also advantageous, when antigens of non-pathogenic strains can be used in the serological examinations. Serological cross-reaction between three taxonomically different strains--Proteus morganii O34 (8662/64), Escherichia coli O111 and Salmonella Adelaide O35--have been described. It has been proven that it is based partially on the similar lipopolysaccharide structures of these pathogens. In this study the involvement of the outer membrane proteins of these strains in the serological cross-reaction is presented. Microfluidic chip technology was applied for the detection of common proteins, which provided fast and quantitative data about the proteins that might be responsible for serological cross-reaction. Two outer membrane proteins with apparent molecular mass of 36 and 41 kDa, respectively, could be detected in the profile of each strain, while individual dominating protein peaks have also appeared in the protein profiles. The presence of common protein antigens was proven by Western blotting.

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.

Expression of a truncated Pasteurella multocida toxin antigen in Bordetella bronchiseptica

Mild or subclinical respiratory infections caused by Bordetella bronchiseptica are widespread in pigs despite multiple control efforts. Infection with virulent B. bronchiseptica strains is a common risk factor in the establishment of toxin-producing strains of Pasteurella multocida in the nasal cavity of pigs leading to the disease, atrophic rhinitis (AR). This study was designed to explore the possibility of expressing a protective epitope of P. multocida toxin (PMT) in B. bronchiseptica to create single-component mucosal vaccine to control atrophic rhinitis in pigs. To achieve this, a P. multocida toxin fragment (PMTCE), that was non-toxic and protective against lethal challenge in mice, was cloned into a broad-host-range plasmid, PBBR1MCS2, and introduced into B. bronchiseptica by electroporation. The Pasteurella gene construct was placed under the regulatory control of a promoter region that was separately isolated from B. bronchiseptica and appears to be part of the heat shock protein gene family. B. bronchiseptica harboring the plasmid under antibiotic selection expressed the 80kDa PMTCE as determined by PAGE and Western blot with a PMT-specific monoclonal antibody. When introduced into the respiratory tracts of mice, B. bronchiseptica harboring the plasmid construct was reisolated in declining numbers for 72h post-inoculation. Antibody responses (IgM, IgA and IgG) to B. bronchiseptica were detected in serum and respiratory lavage, but PMTCE-specific antibodies were not detected. While further refinements of PMT expression in B. bronchiseptica are necessary, this study provides a basis for the development of a single-component, live-attenuated vaccine against atrophic rhinitis.

Evaluation of vaccines for atrophic rhinitis--a comparison of three challenge models

We compared three challenge models for the assessment of atrophic rhinitis (AR) vaccines: combined infection with Bordetella bronchiseptica (Bb) and Pasteurella multocida (Pm); application of acetic acid (AA) to the nasal mucosa followed by Pm infection; and Bb infection alone. Two vaccines were tested using standardized criteria, notably nasal lesion scores. The vaccines provided different levels of protection in the Bb and the AA/Pm challenges, but were similar in the combined (Bb/Pm) challenge. It is clear that the AA/Pm model shows the protective value of only the Pm component, whereas the single Bb challenge reflects the protective value merely of the Bb component of a combined vaccine. These results suggest that the best assessment of protection is provided if the two specific challenges are performed separately.

Two-color hybridization assay for simultaneous detection of Bordetella bronchiseptica and toxigenic Pasteurella multocida from swine

Bordetella bronchiseptica and toxigenic Pasteurella multocida are the etiologic agents of swine atrophic rhinitis. Methods currently used for their identification are time-consuming and suffer from a lack of sensitivity. We describe a colony lift-hybridization assay for detection of B. bronchiseptica and toxigenic P. multocida that can be performed with a single colony lift derived from a primary isolation plate without the need for pure subcultures of suspect bacteria. Membranes are hybridized simultaneously to probes derived from the B. bronchiseptica alcA gene and the P. multocida toxA gene. A multicolor development procedure permits sequential detection of bound probes. The assay was tested with 84 primary isolation plates generated from nasal swabs from swine with clinical signs of atrophic rhinitis. Comparison of the results from the colony lift-hybridization assay with those from conventional testing, based on a combination of colony morphology, biochemical reactions, mouse lethality, and enzyme-linked immunosorbent assay, indicated that the colony lift assay has superior sensitivity and comparable specificity. This technique has wide application for diagnostic and experimental studies.

A porcine model for the evaluation of virulence of Bordetella bronchiseptica

Studies of virulence factors of Bordetella bronchiseptica require a suitable system. Such a system was devised in colostrum-deprived, caesarean-derived pigs, aged 7 d. In two different experiments, pigs (n = 11) were inoculated intranasally with 10(6) colony-forming units of the virulent strain 4609. In the same way, further pigs (n = 11) were inoculated with a strain (B133) of unknown virulence. No significant differences between 4609 and B133 colonization were seen. However, colonization of the turbinates was significantly higher than that of the trachea, lung and tonsil, and a significantly higher degree of colonization was present at 11 d post-inoculation (PI) than at 15 days. Moderate turbinate atrophy was present by 11 d PI, and peribronchiolar fibrosis was present at 15 days. Immunocytochemical methods showed that all pigs had bacterial antigen in the ciliated cells of the turbinates and trachea, and in the lung; some pigs also had antigen in the bronchi. Bacterial antigen was present in some bronchioles and within the cytoplasm of pulmonary macrophages and neutrophils. This model should prove useful for comparing strains of B. bronchiseptica and isogenic mutants deficient in putative virulence factors.

Effect of Bordetella bronchiseptica and serotype D Pasteurella multocida bacterin-toxoid on the occurrence of atrophic rhinitis after experimental infection with B. bronchiseptica and toxigenic type AP. multocida

In efficacy tests, 7 primary specific-pathogen-free piglets vaccinated with the Bordetella bronchiseptica and type D Pasteurella multocida bacterin-toxoid were challenged with B. bronchiseptica and type A P. multocida. Severe or moderate nasal turbinate atrophy was produced in the non-vaccinated pigs, whereas, only one of the 4 pigs in the vaccinated group had slight turbinate atrophy. Other immune sera against crude toxin of P. multocida type A or D were cross neutralized. The results of the present study show that the P. multocida serotype D bacterin-toxoid is effective against atrophic rhinitis caused by toxigenic P. multocida serotype A as well as toxigenic P. multocida serotype D.

Direct PCR analysis for toxigenic Pasteurella multocida

A more rapid, accurate method to detect toxigenic Pasteurella multocida is needed for improved clinical diagnosis, farm biosecurity, and epidemiological studies. Toxigenic and nontoxigenic P. multocida isolates cannot be differentiated by morphology or standard biochemical reactions. The feasibility of using PCR for accurate, rapid detection of toxigenic P. multocida from swabs was investigated. A PCR protocol which results in amplification of an 846-nucleotide segment of the toxA gene was developed. The PCR amplification protocol is specific for toxigenic P. multocida and can detect fewer than 100 bacteria. There was concordance of PCR results with (i) detection of toxA gene with colony blot hybridization, (ii) detection of ToxA protein with colony immunoblot analysis, and (iii) lethal toxicity of sonicate in mice in a test set of 40 swine diagnostic isolates. Results of an enzyme-linked immunosorbent assay for ToxA agreed with the other assays except for a negative reaction in one of the 19 isolates that the other assays identified as toxigenic. In addition to accuracy, as required for a rapid direct specimen assay, toxigenic P. multocida was recovered efficiently from inoculated swabs without inhibition of the PCR. The results show that PCR detection of toxigenic P. multocida directly from clinical swab specimens should be feasible.

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.

Experimental model of atrophic rhinitis in gnotobiotic pigs

To study the pathogenesis of atrophic rhinitis, gnotobiotic pigs (n = 6) were inoculated intranasally with a sterile sonicate of a toxigenic strain of Bordetella bronchiseptica (0.16 mg of protein per ml) at 5 days of age, and they were then inoculated intranasally with 1 ml (5,250 CFU/ml) of a live, toxigenic strain of Pasteurella multocida at 7 days of age. Pigs were necropsied at 2, 5, 9, 14, 21, and 28 days postinoculation; those pigs necropsied after 5 days had developed turbinate atrophy. Other gnotobiotic pigs received the following inoculation protocols: (i) a sterile sonicate of a nontoxigenic strain of B. bronchiseptica (0.2 mg of protein per ml), followed by toxigenic P. multocida (n = 4); (ii) toxigenic P. multocida alone (n = 7); (iii) diluent (sterile tryptose broth) (n = 2); (iv) the sterile sonicate of toxigenic B. bronchiseptica alone (n = 2); or (v) the sterile sonicate of a nontoxigenic strain of B. bronchiseptica alone (n = 2). Turbinate atrophy did not occur in the latter groups except for one pig inoculated with only toxigenic P. multocida. These studies show that turbinate atrophy occurs in pigs given the toxigenic B. bronchiseptica sonicate and then given live, toxigenic P. multocida. This experimental regimen is a useful model for (i) studying the pathogenesis of atrophic rhinitis and (ii) testing vaccine strategies.