Rapid detection of Mycobacterium paratuberculosis in clinical samples from ruminants and in spiked environmental samples by modified BACTEC 12B radiometric culture and direct confirmation by IS900 PCR

The suitability of a radiometric culture medium consisting of BACTEC 12B with PANTA PLUS, mycobactin J, and egg yolk was evaluated for detection of Mycobacterium paratuberculosis in feces, mesenteric lymph nodes, and intestinal walls from cattle, sheep, and goats. In addition, a simple method that would enable the rapid identification of Mycobacterium paratuberculosis by IS900 PCR in the primary cultures was sought so that subculture to secondary egg-free radiometric medium could be avoided. An ethanol extraction followed by differential centrifugation was used to separate M. paratuberculosis from PCR inhibitors in the primary culture. PCR was then undertaken with the pellet, after boiling to lyse the mycobacteria; if this test was negative, the DNA in the lysate was purified with guanidine thiocyanate and silica. Cultures of feces, ilea, and mesenteric lymph nodes from cattle, sheep, and goats known to have or suspected of having Johne's disease yielded positive PCR results 1 to 7 weeks after inoculation. Similar results were obtained with soil and pasture samples that had been spiked with M. paratuberculosis. The results suggested that radiometric culture was more sensitive than histopathology in detecting M. paratuberculosis infection in sheep and goats and more sensitive than culture on Herrold's egg yolk medium for the detection of the infection in cattle. Of 259 individual PCR tests with samples from cultures with growth indices of > or = 10,237 (91.5%) were positive, with only 28 (11.8%) requiring both ethanol and silica preparation to yield a positive result. Of the 22 negative PCR results for samples from cultures with growth indices of > or = 10, 18 were for samples from cultures that had only just developed evidence of growth. PCR-positive cultures tended to remain PCR positive over successive weeks. Flexibility in the timing of the sampling for PCR is thus possible, facilitating batch processing of samples in large-scale disease control programs for ruminants.

Identification and detection of Actinobacillus pleuropneumoniae by PCR based on the gene apxIVA

The apxIVA gene, a recently discovered RTX determinant of Actinobacillus pleuropneumoniae, was shown to be species-specific. DNA hybridization experiments using probes for various regions of apxIVA revealed that the 3'-terminus of this gene was present in all 14 serotypes of A. pleuropneumoniae but absent from phylogenetically related species. A primer pair spanning this region specifically amplified a 422bp fragment in PCR experiments with DNA from the reference strains of the 14 serotypes and 194 field strains isolated from various geographic locations worldwide. DNA sequence analysis of PCR products derived from all serotypes were identical except in serotypes 3, 8, and 10, which showed minor differences. The PCR did not amplify any product when DNA from 17 different bacterial species closely related to A. pleuropneumoniae was used as template. In addition, the PCR was negative with DNA of several Actinobacillus sp. which were initially characterized as A. pleuropneumoniae using routine phenotypic and serological analyses but which were subsequently shown by 16S rRNA sequence analysis to belong to yet undefined Actinobacillus species. The sensitivity of the PCR was determined to be 10pg of A. pleuropneumoniae DNA. A set of nested primers amplified a 377bp fragment specifically with A. pleuropneumoniae DNA. DNA titration experiments using the flanking and nested primer pairs showed an improved level of sensitivity to approximately 10fg of genomic DNA. The nested PCR was used to monitor the spread of A. pleuropneumoniae in pigs experimentally infected with a virulent serotype 1 strain and housed in a controlled environment facility. A. pleuropneumoniae DNA could be detected by nested PCR in nasal swab samples of infected pigs receiving either a high dose (5x10(5)) or a low dose (1x10(4)) challenge and in unchallenged cohorts that were contact-infected by the inoculated animals. Furthermore, PCR confirmed the presence of A. pleuropneumoniae in 16/17 homogenates from necrotic lung lesions, while the bacterium was successfully recovered from 13 of these lesions by culture.

Serum and mucosal antibody responses and protection in pigs vaccinated against Mycoplasma hyopneumoniae with vaccines containing a denatured membrane antigen pool and adjuvant

OBJECTIVE

To investigate the protective efficacy of a pool of denatured membrane protein antigens of Mycoplasma hyopneumoniae (J strain) in the molecular size range 70 to 85 kDa (F3 antigen) in combination with adjuvants for pigs challenged with M hyopneumoniae.

DESIGN

A vaccine efficacy experiment with assessment of serum and respiratory tract antibody responses.

PROCEDURE

F3 antigens were emulsified with five different adjuvants. To groups of three pigs per vaccine, four vaccines were given by intramuscular injection, and two vaccines, including one of those given intramuscularly, were given by intraperitoneal injection.

RESULTS

Compared to six unvaccinated pigs, animals vaccinated with F3 antigen displayed significantly reduced pneumonia (54% reduction in mean lung score) following experimental challenge. Analysis of post-vaccination, pre-challenge IgG and IgA ELISA antibody absorbances in serum and respiratory tract washings revealed no correlation with lung score. Six weeks after challenge, pigs previously vaccinated intramuscularly mostly demonstrated greater IgG and IgA responses in respiratory tract washings, and greater IgG serum antibody responses, than those vaccinated by intraperitoneal injection.

CONCLUSION

Pigs vaccinated with M hyponeumoniae antigens in the molecular size range of 70 to 85 kDa showed a significant reduction in lung lesions compared with unvaccinated control animals after experimental challenge. IgG and IgA antibody concentrations in serum and respiratory tract washings after vaccination do not provide a useful prognostic indicator of protection from enzootic pneumonia.

Mhp182 (P102) binds fibronectin and contributes to the recruitment of plasmin(ogen) to the Mycoplasma hyopneumoniae cell surface

Mycoplasma hyopneumoniae is a major, economically damaging respiratory pathogen. Although M. hyopneumoniae cells bind plasminogen, the identification of plasminogen-binding surface proteins and the biological ramifications of acquiring plasminogen requires further investigation. mhp182 encodes a highly expressed 102 kDa protein (P102) that undergoes proteolytic processing to generate surface-located N-terminal 60 kDa (P60) and C-terminal 42 kDa (P42) proteins of unknown function. We show that recombinant P102 (rP102) binds plasminogen at physiologically relevant concentrations (K(D) ~ 76 nM) increasing the susceptibility of plasmin(ogen) to activation by tissue-specific plasminogen activator (tPA). Recombinant proteins constructed to mimic P60 (rP60) and P42 (rP42) also bound plasminogen at physiologically significant levels. M. hyopneumoniae surface-bound plasminogen was activated by tPA and is able to degrade fibrinogen, demonstrating the biological functionality of M. hyopneumoniae-bound plasmin(ogen) upon activation. Plasmin(ogen) was readily detected in porcine ciliated airways and plasmin levels were consistently higher in bronchoalveolar lavage fluid from M. hyopneumoniae-infected animals. Additionally, rP102 and rP42 bind fibronectin with K(D) s of 26 and 33 nM respectively and recombinant P102 proteins promote adherence to porcine kidney epithelial-like cells. The multifunctional binding ability of P102 and activation of M. hyopneumoniae-sequestered plasmin(ogen) by an exogenous activator suggests P102 plays an important role in virulence.

Comparative sensitivity of various faecal culture methods and ELISA in dairy cattle herds with endemic Johne's disease

In three New South Wales dairy cattle herds with endemic Johne's disease, prevalence rates by faecal culture were determined to be 12, 18 and 22%, respectively. Whole herd faecal culture was shown to detect markedly more infected cattle than whole herd testing by the EMAI absorbed ELISA, particularly in the two herds with greatest prevalence. In the three study herds, five methods for whole herd faecal culture were compared in each. These included two methods based on primary culture on Herrold's egg yolk medium with mycobactin J (HEYM): (1) conventional decontamination with sedimentation and primary culture on HEYM; (2) Whitlock decontamination and culture on HEYM. The remaining three methods were based on radiometric (BACTEC) culture: (3) decontamination and filtration to BACTEC medium; (4) modified Whitlock decontamination to BACTEC medium and (5) Whitlock decontamination to BACTEC medium. For BACTEC cultures, two methods were compared as confirmatory tests for Mycobacterium paratuberculosis: mycobactin dependence on conventional subculture to HEYM and IS900 PCR analysis of radiometric media. Among 179 cattle tested simultaneously by all five culture methods, 38 cattle were confirmed to be shedding M. paratuberculosis. In identifying shedder cattle, method 5 was the most sensitive, followed by methods 2, 4, 1, and 3 was the least sensitive. The number of BACTEC cultures confirmed by mycobactin dependence or PCR was similar.

DNA fingerprinting of Australian isolates of Mycobacterium avium subsp paratuberculosis using IS900 RFLP

OBJECTIVES

To evaluate additional restriction enzymes for IS900 RFLP of Mycobacterium avium subsp paratuberculosis and examine the genetic diversity among Australian isolates for epidemiological studies of Johne's disease.

DESIGN AND PROCEDURE

Seventy-one isolates of M paratuberculosis from cattle, sheep, goat, alpaca and rhinoceros in six Australian States and the Northern Territory, reference strains and reference DNA from previously characterised strains were tested for genetic variation. Bst EII, Pvu II and Pst I restriction enzymes were used, and four others (Bam HI, Alu I, Xho I and Dra I) were assessed for their ability to detect polymorphisms. Multiple isolates from some animals were tested.

RESULTS

Bam HI, was the most effective enzyme for identifying polymorphisms (12 types), followed by Bst EII (11 types). Both Pvu II and Pst I were relatively ineffectual. Fifteen different types were identified, 12 in clinical isolates. Most isolates were cattle (C) strains and fell into the C1 (n = 28) and C3 (n = 32) groupings. All isolates from alpaca were type C1, and bovine isolates were commonly C1 (n = 15) or C3 (n = 28). All of the sheep were infected with sheep (S) strains; no S strains were identified in cattle. Two of six isolates from one animal had single band differences.

CONCLUSION

The epidemiological features of M paratuberculosis in Australia are similar to those reported in New Zealand, where cattle and sheep are commonly infected with different strains. However, because of the lack of polymorphism identified within the major groups, it is unlikely that DNA fingerprinting will have a significant role in epidemiological studies of Johne's disease, unless an unusual strain in being studied.

Evaluation of a Pourquier ELISA kit in relation to agar gel immunodiffusion (AGID) test for assessment of the humoral immune response in sheep and goats with and without Mycobacterium paratuberculosis infection

The present study was designed to evaluate a commercial ELISA kit (Institut Pourquier) for the diagnosis of ovine and caprine paratuberculosis under Australian conditions and to compare its accuracy with the existing AGID test. The sensitivity of the ELISA in sheep and goats was 34.9% and 56.4%, with a specificity of 98.8% and 100.0%, respectively. Sensitivity of AGID was 13.8% for sheep and 39.5% for goats, with specificity of 100.0% for both species. The sensitivity of the ELISA in sheep depended on the category of histological lesions. AGID and ELISA were conditionally independent, and appeared to detect overlapping but distinct subgroups of infected animals. The ELISA was significantly more sensitive than the AGID. The ELISA was simple to perform, robust and repeatable. Coefficients of variation of <12.0% were observed for positive and negative controls included on 193 plates over a 10-month period and there was a high level of intraassay repeatability with 12.0% of the duplicate samples having CV of >15.0%.

Evaluation of an absorbed ELISA and an agar-gel immuno-diffusion test for ovine paratuberculosis in sheep in Australia

The sensitivities and specificities of an absorbed enzyme-linked immunosorbent assay (ELISA) and an agar-gel immuno-diffusion (AGID) test for the detection of Johne's disease in sheep were estimated using data from six known infected and 12 assumed uninfected sheep flocks. Sensitivities were estimated for all histologically positive sheep, as well as by histological lesion score, lesion type (paucibacillary or multibacillary) and sheep body-condition score, with ELISA sensitivities estimated at 95 and 99% specificity. Logistic-regression analysis was used to test for significant effects of lesion score and condition score, with flock included in the model as a random effect. Estimated specificities were 95% (95% CI: 93.4, 95.6%) and 99% (98.4, 99.4%) for ELISA cut-point ratios of 2.4 and 3.6, respectively, and 100% (99.7, 100.0%) for the AGID. Estimated sensitivities for all infected sheep were 41.5% (35.0, 48.3%), 21.9% (16.6, 27.9%) and 24.6% (19.1, 30.7%) for ELISA cut-point ratios of 2.4 and 3.6 and for AGID, respectively. Sensitivities of all tests and cut-points varied significantly between flocks and between categories of lesion score and condition score. Sensitivity ranged from 25 to 73, 10 to 47 and 9.2 to 63% between flocks, for the ELISA with cut-points of 2.4 and 3.6, and for the AGID, respectively. Sensitivity was highest in thin sheep and in sheep with multibacillary lesions. The effects of lesion type and condition score on test sensitivity were significant in the logistic regressions for the AGID and ELISA at both cut-points and the flock effect was significant for the AGID but not for the ELISA at either cut-point.

Serotypes of Erysipelothrix rhusiopathiae in Australian pigs, small ruminants, poultry, and captive wild birds and animals

Serotypes of 93 Australian isolates of Erysipelothrix rhusiopathiae from diseased domestic animals and poultry and a variety of captive wild birds and animals were determined by double diffusion gel precipitation. Two isolates, from the faeces of a swallow were also examined. Serotypes 1a, 1b and 2 were isolated from pigs and serotypes 1a, 1b, 2, 5, 15 and 21 from sheep or goats. Erysipelas in poultry was attributed to serotypes 1b, 5, 15 and 16. In captive wild birds serotypes 1b, 5, 6, 8, 14, 21 and an isolate reactive with antiserum to strain Seehecht were associated with septicaemic deaths. Single isolates from tissues of a bilby (Macrotis lagotis), black rat (Rattus rattus), brown snake (Pseudechis australis) and a bandicoot (Isoodon macrouris) were classified as serotypes 4, 4, 7, and 10 respectively. Six isolates were not able to be typed. Serotype 1b was the most widely distributed and most common (28%), being associated with disease in pigs, sheep, poultry and wild birds. Serotypes 1a or 2 were found in a more restricted range of animals, being commonly associated with erysipelas in pigs, less commonly in sheep and infrequently in other species. From diseased pigs, 26 of 33 isolates (79%) were serotypes 1a and 1b.

Analysis of Erysipelothrix rhusiopathiae and Erysipelothrix tonsillarum by multilocus enzyme electrophoresis

The genetic diversity of 74 Australian field isolates of Erysipelothrix rhusiopathiae and 22 reference strains for serovars of E. rhusiopathiae or Erysipelothrix tonsillarum was examined by multilocus enzyme electrophoresis. Four serovar reference strains of E. tonsillarum (strains KS 20 A, Wittling, Lengyel-P, and Bano 107 for serovars 25, 3, 10, and 22, respectively) were genetically distinct from E. rhusiopathiae. However, the E. tonsillarum reference strain for serovar 14 (Iszap-4) and the reference strain for serovar 13 (Pecs-56), which has been said to represent a new genomic species, were found to cluster with typical isolates and reference strains of E. rhusiopathiae. Our reference strain for serovar 7 (Rotzunge) was also genetically typical of E. rhusiopathiae, thus indicating that these serotype reactivities cannot be relied upon as a means of identifying isolates as E. tonsillarum. Australian field isolates of E. rhusiopathiae were genetically diverse. Those recovered from sheep or birds were more diverse than those isolated from pigs, and isolates of serovar 1 were more diverse than those of serovar 2. The diversity found among isolates of the same serovar and the presence of isolates of different serovars in the same electrophoretic types (ETs) indicated that serotyping of E. rhusiopathiae was unreliable for use as an epidemiological tool. Some ETs contained isolates recovered from different animal species. ET 41 contained 32.2% of the field isolates and two reference strains, indicating that this clone of E. rhusiopathiae is both widespread and commonly associated with disease in various species of animals.

Oral immunization of swine with attenuated Salmonella typhimurium aroA SL3261 expressing a recombinant antigen of Mycoplasma hyopneumoniae (NrdF) primes the immune system for a NrdF specific secretory IgA response in the lungs

Salmonella typhimurium SL3261 (aroA mutant) expressing a recombinant Mycoplasma hyopneumoniae antigen was used to orally immunize swine against porcine enzootic pneumonia. This construct, designated S. typhimurium aro A SL3261 (pKF1), expressed a recombinant protein containing the carboxy-terminal 11 kDa of a 42 kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Here we demonstrate that this antigen is present in all seven geographically diverse strains of M. hyopneumoniae tested, and is recognized by the swine immune system after experimental infection with the virulent M. hyopneumoniae Beaufort strain. The immune response of swine orally immunized twice with S. typhimurium SL3261 (pKF1) on day 0 and day 14 was evaluated. Oral immunization with S. typhimurium SL3261 (pKF1) primed the immune system to elicit a significant (P<0.05) secretory IgA response against the 15 kDa NrdF antigen in the respiratory tract of swine, post-challenge, compared to control groups. Blood lymphocytes from swine immunized with S. typhimurium SL3261 (pKF1) proliferated significantly (P<0.05) following stimulation with M. hyopneumoniae whole-cell extracts compared to control groups 14 days post-vaccination. Following challenge with virulent M. hyopneumoniae, swine immunized with S. typhimurium SL3261 (pKF1) showed higher average daily weight gains and reduced lung pathology compared to control groups.

Molecular characterization of a ribonucleotide reductase (nrdF) gene fragment of Mycoplasma hyopneumoniae and assessment of the recombinant product as an experimental vaccine for enzootic pneumonia

A Mycoplasma hyopneumoniae clone bank was screened with hyperimmune pig serum. One clone exhibited sequence homology to the prokaryotic R2 subunit of ribonucleotide reductase and was expressed as an 11-kDa protein fused to beta-galactosidase. The vaccine potential of the fusion protein was assessed in pig trials. Following experimental challenge with a virulent isolate of M. hyopneumoniae, gross lung pathology (mean Goodwin lung score) of vaccinated animals, irrespective of adjuvant treatment, was significantly reduced compared with that of control unvaccinated pigs (P < 0.05).

Molecular fingerprinting of Pasteurella multocida associated with progressive atrophic rhinitis in swine herds

Ninety-six nasal isolates of Pasteurella multocida from swine herds with progressive atrophic rhinitis were characterized by restriction endonuclease analysis (REA) of whole-cell DNA, ribotyping, and plasmid analysis. For REA, bacterial DNA was digested with SmaI and electrophoresed in 0.7% agarose, and fragments were visualized with UV light. For ribotyping, EcoRI-digested and electrophoresed restriction fragments of whole-cell DNA were transferred to nitrocellulose membranes, hybridized with gamma-32P-labeled Escherichia coli ribosomal RNA, and visualized by autoradiography. Phenotypes of isolates were toxigenic capsular type D (n = 51), nontoxigenic type D (n = 28), nontoxigenic type A (n = 16), and toxigenic type A (n = 1). Plasmids of various sizes were evident in 92.2% and 17.9% of toxigenic and nontoxigenic D strains, respectively, but were absent from all type A strains. Among the 4 phenotypes, there were 17 REA profiles and 6 ribotypes. For 3 of 17 REA patterns, multiple ribotypes were evident, and several REA types were evident in 5 of 6 ribotypes. Thirty-seven isolates of toxigenic capsular type D from Australian herds were either SmaI type B or C and ribotype 2, whereas 14 toxigenic D isolates from the USA and other countries were more heterogeneous (7 REA types and 6 ribotypes). The fingerprinting results provided evidence in support of the hypothesis of a single source infection in Australia associated with the introduction of breeding pigs from overseas.

Oral immunization of mice with attenuated Salmonella typhimurium aroA expressing a recombinant Mycoplasma hyopneumoniae antigen (NrdF)

Mycoplasma hyopneumoniae is the etiological agent of porcine enzootic pneumonia, a commercially expensive respiratory disease of swine. Salmonella typhimurium SL3261 was used as a live carrier of plasmid pKF1, which encodes a 15-kDa recombinant M. hyopneumoniae protein. This expressed recombinant protein consists of the carboxy-terminal 11 kDa of a 42-kDa M. hyopneumoniae NrdF ribonucleotide reductase R2 subunit protein. Rabbit anti-15-kDa serum was able to inhibit the growth of viable M. hyopneumoniae J in vitro. When used as a live oral vaccine, S. typhimurium SL3261(pKF1) induced a significant secretory immunoglobulin A immune response in the lungs of mice orally immunized against the M. hyopneumoniae antigen. Utilization of live oral vaccines expressing potentially protective M. hyopneumoniae proteins, such as the NrdF antigen, which can stimulate a lung mucosal response against surface-accessible proteins may provide a cost-effective alternative to the present control strategies used for porcine enzootic pneumonia.

Plasmin activity in the porcine airways is enhanced during experimental infection with Mycoplasma hyopneumoniae, is positively correlated with proinflammatory cytokine levels and is ameliorated by vaccination

In Mycoplasma hyopneumoniae (Mhp) infection of swine, the host immune response is considered a major driver of lung pathology; however the underlying inflammatory mechanisms are not well understood. The serine protease plasmin is being increasingly recognised as a significant player in inflammatory processes. Here we compare plasmin activity in tracheobronchial lavage fluid (TBLF) from pigs experimentally challenged with Mhp that were either unvaccinated (n=10), or vaccinated with the commercial vaccine Suvaxyn(®) M.hyo (n=10). TBLF collected immediately prior to challenge and at 21 d and 35 d post-challenge was also assayed for levels of proinflammatory cytokines (TNF-α, IL-1β and IL-6), and for bacterial load (by qPCR). Clinical signs, pathology, cytokine analyses and qPCR all indicated that vaccinated pigs had significantly reduced disease relative to unvaccinated animals. Plasmin activity increased significantly in TBLF collected at 21 d post-challenge compared to pre-challenge TBLF in unvaccinated (P<0.01), but not vaccinated animals (P>0.05). A significant correlation was observed between bacterial load and plasmin activity in the 21 d (r=0.66; P<0.01) and the 35 d post-challenge samples, (r=0.62; P<0.01). Plasmin activity was also significantly correlated with levels of TNF-α, IL-1β and IL-6 at 21 d (r=0.78, P<0.0001; r=0.77, P<0.0001; r=0.64, P<0.005) and with TNF-α and IL-1β at 35 d post-challenge (r=0.77, P<0.0001; r=0.74, P<0.0005). Our results indicate that plasminogen is activated to plasmin in the respiratory tract of pigs as part of the host inflammatory response to Mhp infection and that this effect is ameliorated by vaccination.

Specificity of absorbed ELISA and agar gel immuno-diffusion tests for paratuberculosis in goats with observations about use of these tests in infected goats

OBJECTIVE

To determine the specificity of serological tests that are currently used in veterinary diagnostic laboratories in Australia for detection of Mycobacterium avium subsp paratuberculosis infection in goats.

DESIGN

A laboratory study.

PROCEDURE

Four tests were studied, comprising AGID with M. a. paratuberculosis antigen derived from cattle isolates of caprine or bovine origin, the EMAI caprine Johne's disease absorbed ELISA and the CSL PARACHEK Johne's absorbed EIA. The specificities of AGID and ELISA for paratuberculosis (Johne's disease) were estimated after examining a panel of 1000 serum samples collected from goats in Western Australia, a region free of paratuberculosis. In addition a comparison was made of test performance in a small number of paratuberculous goats from New South Wales using sera from two archival collections.

RESULTS

The specificity of the AGID tests was 100% while the specificities of the two absorbed ELISA were 99.7 to 99.8% at appropriate positive-negative cut-offs. Based on testing the small sample of sera from infected goats, the absorbed ELISA tests detected about twice as many goats with Johne's disease as the AGID. Each test detected paratuberculous animals regardless of whether infection was caused by cattle or sheep strains of M. a. paratuberculosis.

CONCLUSIONS

Both ELISA and AGID tests for paratuberculosis have high specificity and can be used in a market assurance program without risk of generating large proportions of false positive test results. However, the results suggested the ELISA is more sensitive for detection of infected goats and should be used in preference to the AGID. The two formats of ELISA evaluated in this study have similar characteristics and could be used in paratuberculosis control programs for the goat industries, but further data on sensitivity would increase confidence in their application.

Skeletal abnormalities in young horses associated with zinc toxicity and hypocuprosis

Four young horses grazing pastures near industrial plants developed illthrift, lameness and skeletal abnormalities characterised by periarticular enlargement of the long bones. The clinical signs and lesions were attributed to hypocuprosis induced by an excessive intake of zinc from pasture. High pasture intakes of iron may have further compounded the problem.

Demonstration that Australian Pasteurella multocida isolates from sporadic outbreaks of porcine pneumonia are non-toxigenic (toxA-) and display heterogeneous DNA restriction endonuclease profiles compared with toxigenic isolates from herds with progressive atrophic rhinitis

Capsular types A and D of Pasteurella multocida cause economic losses in swine because of their association with progressive atrophic rhinitis (PAR) and enzootic pneumonia. There have been no studies comparing whole-cell DNA profiles of isolates associated with these two porcine respiratory diseases. Twenty-two isolates of P. multocida from diseased pigs in different geographic localities within Australia were characterised genotypically by restriction endonuclease analysis (REA) with the enzyme CfoI. Seven of 12 P. multocida isolates from nasal swabs from pigs in herds where PAR was either present or suspected displayed a capsular type D phenotype. These were shown to possess the toxA gene by polymerase chain reaction (PCR) and Southern hybridisation, and further substantiated by production of cytotoxin in vitro. The CfoI profile of one of these seven isolates, which was from the initial outbreak of PAR in Australia (in Western Australia, WA), was identical with profiles of all six other toxigenic isolates from sporadic episodes in New South Wales (NSW). The evidence suggests that the strain involved in the initial outbreak was responsible for the spread of PAR to the eastern states of Australia. Another 10 isolates, representing both capsular types A and D, were isolated exclusively from porcine lung lesions after sporadic outbreaks of enzootic pneumonia in NSW and WA. CfoI restriction endonuclease profiles of these isolates revealed considerable genomic heterogeneity. Furthermore, none of these possessed the toxA gene. This suggests that P. multocida strains with the toxA gene do not have a competitive survival advantage in the lower respiratory tract or that toxin production does not play a role in the pathology of pneumonic lesions, or both. REA with polyacrylamide gel electrophoresis and silver staining was found to be a practical and discriminatory tool for epidemiological tracing of P. multocida outbreaks associated with PAR or pneumonia in pigs.

Characterisation of Erysipelothrix rhusiopathiae isolates from pigs associated with vaccine breakdowns

Swine erysipelas vaccines are routinely used to protect pigs against peracute and acute/urticarial forms of Erysipelothrix. Between 1995 and 1998, 34 swine herds across four Australian states experienced vaccine failure. Forty-four isolates of Erysipelothrix rhusiopathiae of serovars 2, 1a, 1b and 1bx21 were recovered from 15 of these 34 vaccine breakdown herds. These isolates were characterised by restriction fragment length polymorphism (RFLP) analyses using RsaI and AluI on whole cell DNA and for the presence of plasmid DNA. Results were compared with those of 20 isolates from 16 herds unaffected by vaccine breakdown and 13 isolates representing 10 reference strains. The majority of breakdown herds possessed isolates of serovar 2 (9/15 herds), followed by serovar 1a (5 herds). No geographic predominance of a single serovar was evident. The identification of 10 RsaI profiles from whole cell DNA among the 44 isolates from 15 breakdown herds indicated that a single, new clonal lineage of E. rhusiopathiae was not responsible for vaccine failure. RsaI RFLP analyses detected a further 14 distinct profiles among 20 field strains unassociated with vaccine breakdowns, and none matched profiles of the 10 serovar reference strains for serovars 1a, 1b, 2 or 21. This technique is recommended for epidemiological studies of E. rhusiopathiae strains.

Manipulating systemic and mucosal immune responses with skin-deliverable adjuvants

Most medically important bacterial and viral pathogens gain entry into the body either via the skin or a mucosal surface. Vaccination provides a viable and cost-effective strategy for the prevention of such diseases and it has always been a principal aim with vaccinologists, to be able to promote simultaneously, protective immune responses both systemically and at mucosal surfaces. The paradigm that mucosal immunity is best stimulated by exposure to antigen via a mucosal route simply because inductive sites such as Peyer's patches and bronchial associated lymphoid tissues are located in the mucosal epithelium, has promoted a plethora of immunizing strategies aimed at delivering both antigen and adjuvant to mucosal surfaces. We have developed a novel adjuvant system capable of intradermal delivery of antigens complexed in an ISCOSOME delivery vehicle. This adjuvant, referred to as a skin and mucosal adjuvant or SAMA4, was efficacious in eliciting both systemic and mucosal IgG and IgA antibodies in sheep, pigs and mice. SAMA4 does not induce granulomatous lesions at the site of vaccine delivery and can be used to deliver adjuvanted antigens by other routes including intranasal, oral and intravaginal. Using ovalbumin as a test antigen, intradermally delivered ovalbumin-SAMA4 complexes was found to be very effective in promoting a cytotoxic T cell response. Attempts to dissect the mode of action of SAMA4 by flow cytometric analysis of lymphocyte populations from the spleen, lung, liver and thymus revealed an effect of route of vaccine delivery upon the composition of specific lymphocyte subsets in these various organ compartments. From this, it can be inferred that SAMA4 induced a route-dependent re-mobilization and alteration in lymphocyte trafficking patterns. Other mucosal adjuvants such as cholera toxin B and microspheres, when injected intradermally, tended to promote primarily, an IgG and not an IgA response against hte carrier antigen.

Serological, bacteriological and pathological changes in rams following different routes of exposure to Brucella ovis

Mature Merino rams were exposed to Brucella ovis by contact with infected semen, using either ewe transmission, intrapreputial, intranasal or intrarectal inoculation of infected semen or intrapreputial inoculation of B. ovis culture. Thirty-six of the 41 rams developed significant complement fixation (CF) test titres, but only 9 of these reactors showed clinical, bacteriological or pathological evidence of infection. Infection occurred in some of the rams from all groups. The results are discussed in relation to the transmission of the disease and the significance of CF titres in rams exposed to B. ovis.