The molecular epidemiology of four outbreaks of porcine pasteurellosis

Biochemical profiles, restriction endonuclease analysis (REA) and ribotyping were used to investigate a total of 38 Pasteurella multocida isolates from four separate outbreaks of pasteurellosis in Australian piggeries. Six isolates were obtained from Outbreak 1, 16 from Outbreak 2 and eight each from outbreaks 3 and 4. Outbreaks 1 and 2 were cases of pneumonic pasteurellosis while outbreaks 3 and 4 involved systemic pasteurellosis. Biochemical characterisation established that a number of different types of P. multocida were present in outbreaks 1 and 3 while outbreaks 2 and 4 were associated with a single type of P. multocida. Outbreaks 1 and 3 yielded isolates of P. multocida that belonged to the subspecies multocida and gallicida, with the subspecies multocida isolates being identified as biovar 3 (6 in total) or 12 (1 in total) and the subspecies gallicida isolates (7 in total) being identified as biovar 8. All 24 isolates from outbreaks 2 and 4 belonged to the subspecies multocida and were all biovar 3. REA and ribotyping showed that, in outbreaks 1 and 3, there were three different types of P. multocida in each outbreak with no common strains between the outbreaks. The molecular methods showed that only a single strain of P. multocida was associated with outbreaks 2 and 4, although the outbreaks were associated with strains that differed in REA profiles but shared a ribotype profile. This study has shown that both, systemic and pneumonic pasteurellosis can be associated with either a single strain or multiple strains of P. multocida. The results also indicate that the molecular typing methods of REA and ribotyping are superior to biochemical characterisation for epidemiological investigation of porcine pasteurellosis.     

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.     

Genetic diversity and associated pathology of Pasteurella multocida isolated from porcine pneumonia

Pasteurella multocida is a widespread respiratory pathogen in pigs associated with atrophic rhinitis and contributing to aggravation of the pulmonary lesions. The aims of the present study were to characterize isolates of P. multocida from porcine bronchopneumonia by pulsed-field gel electrophoresis (PFGE), PCR based capsular typing and multilocus sequence typing (MLST) and to compare clonal complexes outlined with the type of histological lung lesions to investigate if a correlation between clonal lineages and lesions might exist. Isolates of P. multocida were obtained from cases of cranioventrally located porcine bronchopneumonia. All lung lesions were described and classified according to histological lesions. A total of 139 isolates, from lung (n=111), pericardial sac (n=21) and kidney (n=7) of 111 pigs were described using PFGE with ApaI as the restriction enzyme. Furthermore, 20 and 29 isolates were characterized by capsular serotyping and multilocus sequence typing, respectively. PFGE demonstrated 15 different clusters showing 50% or more similarity. All selected isolates were of capsular serotype A and only three main sequence types (ST) were detected among the isolates. Associations were not found between histopathology and clonal complexes of P. multocida. In conclusion, PFGE demonstrated a high diversity of genotypes of P. multocida associated with porcine bronchopneumonia. However, isolates obtained mainly belonged to few STs, indicating that isolates of P. multocida associated with porcine bronchopneumonia originates from a limited number of clonal lineages and therefore might have adapted to porcine hosts. No correlation was demonstrated between genotypes and types of lesions, and extra-pulmonary spreading was only rarely demonstrated.     

Profiling of virulence associated genes of Pasteurella multocida isolated from cattle

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

Virulence of raptor-origin Pasteurella multocida in domestic chickens.

Pasteurella multocida belonging to somatic serotype 1 and capsular type A has been known to cause avian cholera in domestic poultry. Pasteurella multocida serotype 1 has also been isolated from raptorial birds. However, the capsular type for these raptorial isolates remains unknown. Moreover, the virulence of these raptorial isolates for domestic poultry has not been determined. The objectives of this study were to determine the capsular type of raptorial P. multocida serotype 1 isolates and to determine if these isolates were virulent for domestic chickens. Study chickens were inoculated with one of three P. multocida isolates. Isolate WESO-1 was obtained from a western screech owl (Otus kennicottii) and isolates RTHA-2 and RTHA-4 were isolated from two red-tailed hawks (Buteo jamaicensis). These isolates were given by either the oral, intravenous, or intraocular route. Control birds were given brain-heart infusion broth. The capsular serotypes of three isolates were also determined. The RTHA-2 and RTHA-4 isolates belonged to P. multocida capsular type A. The WESO-1 isolate belonged to capsular type F. Results also demonstrated that, for the isolates examined, the intraocular route did not cause mortality in chickens. There was mortality in all groups for the intravenous route. However, various mortality patterns were observed when P. multocida was given orally for the three different isolates. The RTHA-4 isolate (serotype 1:A) was the most virulent for domestic chickens. The WESO-1 isolate (serotype 1:F) was the least virulent for chickens among the raptorial isolates examined.     

Phenotypic and genotypic characterisation of Pasteurella multocida isolated from pigs at slaughter in New Zealand

AIMS: To examine pigs at slaughter in New Zealand for the presence of Pasteurella multocida, and to determine for isolates, their biochemical profiles, somatic and capsular types, and the presence or absence of the HSB and toxA genes, associated with haemorrhagic septicaemia (HS) and progressive atrophic rhinitis (PAR), respectively. METHODS: Swabs from 173 lungs, 158 palatine tonsils and 82 nasal passages of pigs at two abattoirs in New Zealand were cultured for P. multocida using conventional techniques, and isolated colonies were subjected to biochemical tests for identification of biovars. Somatic serotyping was conducted using an agar gel immunodiffusion (AGID) test. Polymerase chain reaction (PCR) assays were used to confirm phenotypic identification of colonies using species-specific primers, capsule type using serogroup-specific primers and multiplex PCR, and to test for the presence of HSB and toxA genes. RESULTS: Pasteurella multocida was isolated from 11/173 (6.4%) lung, 32/158 (20.2%) palatine tonsil and 5/82 (6.1 %) nasal swab samples, a total of 48 isolates from 413 samples (11.6%). Isolation rates per farm ranged from 1-53% of tissue samples collected from pigs 5-6 months of age. On phenotypic characterisation, isolates were allocated to seven main biovars, viz 1, 2, 3, 5, 9, 12, and a dulcitol-negative variant of Biovar 8, the majority (30/48) being Biovar 3. Of the 42 isolates for which somatic serotyping was conducted, 10% were Serovar 1, 79% were Serovar 3, 2% were Serovar 6,1, 2% were Serovar 12, and 7% could not be typed. All 48 isolates were confirmed as P. multocida using a species-specific PCR. In the capsular multiplex PCR, 92% of isolates were Capsular (Cap) type A, 2% were Cap D, and 6% could not be typed. None of the samples were positive for the HSB or toxA genes. CONCLUSION: Serovars or capsular types of P. multocida associated with HS or PAR in pigs were not detected. Establishment of species-specific, capsular and toxin PCR assays allowed the rapid screening of isolates of P. multocida, while serotyping provided an additional tool for epidemiological and tracing purposes.     

Molecular characterisation of avian Pasteurella multocida isolates from Australia and Vietnam by REP-PCR and PFGE

A total of 95 isolates of Pasteurella multocida were analysed by pulsed field gel electrophoresis (PFGE) using the enzyme ApaI, including 73 avian isolates from Australia and 22 from Vietnam. The majority of field isolates were capsular Type A, with the predominant somatic serovars of 1, 3, 4 and 3,4. Twenty-one distinct profiles were evident among the Australian isolates, with only 3 profiles observed among the 22 P. multocida strains isolated from Vietnam. Within the Australian isolates, related and unrelated outbreaks could be identified by PFGE. These results correlated well with previously published studies, with greater discrimination shown by PFGE. Repetitive extragenic palindromic sequence PCR (REP-PCR) analysis of representative isolates from PFGE classifications yielded 21 profiles, with most of the subgroups in accordance with PFGE analysis. While REP-PCR was shown to be less discriminating than PFGE, the epidemiological relatedness of strains compared favourably between the techniques. Thus, the ease and rapidity of REP-PCR while maintaining a high level of differentiation, supports the use of REP-PCR as a competent alternative to the more labour-intensive PFGE system for strain identification and epidemiological studies of avian P. multocida.     

Epidemiology of Pasteurella multocida in a farrow-to-finish swine herd.

Thirty-eight clinical isolates of Pasteurella multocida, recovered from a continuous flow, farrow-to-finish swine herd, were characterized by capsular serotyping and restriction endonuclease analysis (REA) in order to study the epidemiology of P. multocida pneumonia. Twenty-three of the 38 isolates obtained in the study belonged to serotype A. They displayed three REA patterns after digestion with HpaII, of which one designated A-3 represented 70% of the samples. The remaining 15 isolates were serotype D. Four different REA patterns were observed in the type D isolates. The REA type D-1 was most prevalent and accounted for 47% of the serotype D isolates. All serotype A isolates were nontoxigenic, whereas five (33%) of the serotype D isolates were toxigenic. Vertical transmission of P. multocida could not be demonstrated, and was probably not a major route of infection. The results of this study suggest that strains of P. multocida virulent for pigs exist and cause swine pneumonic pasteurellosis in continuous flow herds by horizontal transmission.     

Identification of Pasteurella multocida isolates of ruminant origin using polymerase chain reaction and their antibiogram study

A total of 100 isolates of Pasteurella multocida from various ruminant species (cattle, buffalo and sheep) belonging to different parts of country were identified using Pasteurella multocida-PCR (PM-PCR) and capsular PCR assays. PM-PCR revealed an amplicon of approximately 460 bp in all the isolates tested. As regards capsular PCR, 36 of 38 cattle isolates and 30 of 34 buffalo isolates were found to belong to capsular serogroup B whereas rest of the cattle and buffalo isolates belonged to serogroup A of P. multocida. In case of sheep, a total of 26 out of 28 isolates were positive for serogroup A specific PCR while remaining 2 amplified a PCR product specific for serogroup F of P. multocida. All the isolates were subjected to antibiotic sensitivity testing using 17 different antibiotics. Enrofloxacin was found to be most potent antibiotic as it was effective against 94% of the isolates followed by ofloxacin (93%), chloramphenicol (93%), doxycycline (89%), tetracycline (86%) and ciprofloxacin (84%). Vancomycin, bacitracin and sulfadiazine were ineffective against P. multocida isolates showing 84%, 75% and 82% resistance, respectively. Further, the antibiogram also revealed the development of resistance against multiple drugs among various isolates of the organism.     

Comparative analyses of Pasteurella multocida strains associated with the ovine respiratory and vaginal tracts

Thirty-five isolates of Pasteurella multocida from the vagina and respiratory tract of sheep were compared by analysing their capsular polysaccharide types and outer membrane protein profiles. The phylogenetic relationships of selected isolates with respect to reference strains of P. multocida were also determined by comparative 16S rRNA sequence analysis. Three capsular types, A, D and F, and three major outer membrane protein types were identified, and there were four different combinations of these characteristics which probably marked four individual clones of P. multocida. Strains representing three of these clones were recovered from cases of ovine pneumonia, whereas isolates of the fourth clone were associated exclusively with the vagina of healthy ewes and the liver of a dead septicaemic lamb on the same farm. Analysis of the 16S rRNA sequences showed that there was 100 per cent identity between representative pneumonic isolates and reference strains of P. multocida subspecies galliseptica and P. multocida subspecies multocida. The 16S rRNA genes of representative vaginal and liver isolates from the same farm were identical but differed from the other strains at one nucleotide position, providing strong evidence that the vaginal and liver isolates represent a distinct subpopulation of P. multocida.     

Prevalence and characteristics of Pasteurella multocida in commercial turkeys

The oropharyngeal regions of 680 meat turkeys and 55 breeder turkeys from nine outbreak farms, three history-outbreak farms, and 19 nonoutbreak farms in Ohio, Indiana, and Pennsylvania were cultured to determine the prevalence of Pasteurella multocida in turkeys. Pasteurella multocida was recovered from 32 out of 105 turkeys belonging to outbreak farms. Pasteurella multocida was not recovered from either history-outbreak or nonoutbreak farms. Characterization via capsular and somatic serotyping, biotyping, restriction endonuclease analysis, and antimicrobial susceptibility testing was performed on all recovered P. multocida isolates. Pasteurella multocida serotype A:1 and somatic serotype 1 with an un-typable capsular serogroup (UT:1) were the most common serogroups found. All isolates belonged to biotype P. multocida ssp. multocida. EcoRI, HpaII, and HindIII restriction enzyme digestions identified three, five, and five restriction fragment length polymorphism profiles, respectively. A majority of the isolates were susceptible to amikacin, ampicillin, ceftiofur, cephalothin, enrofloxacin, florfenicol, gentamicin, neomycin, novobiocin, oxacillin with 2% NaCl, sarafloxacin, tilmicosin, and trimethoprim with sulphadiazine and resistant to clindamicin, penicillin, tiamulin, and tylosin.     

Virulence genotype of Pasteurella multocida strains isolated from different hosts with various disease status

To learn more about the molecular biology of Pasteurella multocida 289 strains isolated from various clinically healthy and diseased hosts were examined for capsule biosynthesis genes (capA, B, D, E, and F) and 14 virulence associated genes by PCR and DNA-DNA-hybridization. As expected, capsule type A strains were highly adapted to bovines (92.3%) and poultry (85.7%) while we mainly found capA (34.9%)- and capD (58.1%)-positive strains in swine. A noticeable amount of capD-positive strains also originated from small ruminants (34.9%) and capF was detected in wild type strains from diseased cattle (2.2%) and cats (7.4%). None of the isolates harboured capE, while capB was exclusively found in all strains from buffaloes. Nearly all isolates showed a combination of genes encoding outer membrane proteins, colonization factors, iron aquisition factors and superoxid-dismutases without any clue for host specificity. In contrast, the transferrin binding protein encoding gene tbpA (31.5%) was limited to ruminant strains and only 37.0% of all P. multocida strains harboured pfhA, coding for a filamentous hemagglutinin, supposed to be a putative adhesion- und serum resistance factor. PfhA revealed a strong positive association to the outcome of disease in bovine hosts and in combination with toxA to that in swine. The dermonecrotoxin encoding toxA, present in 12.5% of all strains, was detected in isolates from swine, small ruminants, cattle, and poultry. A significant association to the disease status, however, was only existent in swine, although with 66.7% we found a notably high prevalence of the toxin gene among strains from small ruminants. The genes toxA, tbpA and pfhA as well as capsule biosynthesis genes are supposed to be important epidemiological marker genes for characterizing P. multocida field strains.     

Characterization of nine Pasteurella multocida isolates from avian cholera outbreaks in Indonesia

Avian cholera outbreaks have been identified in Indonesia in recent years. Despite vaccination programs, outbreaks continue to occur. To date, there has been a lack of information on the characteristics of Pasteurella multocida isolates involved in these outbreaks. Hence, the objective of this study was to characterize Indonesian P. multocida isolates in poultry. During 1998-99, 20 field outbreaks were reported in Indonesia. Nine isolates of P. multocida were recovered from these field outbreaks. The isolates were compared with four vaccine strains that were used in Indonesia and designated PM-V1, PM-V2, PM-V3, and PM-V4. The isolates were characterized by biotype, capsular type, somatic serotype, restriction endonuclease analysis, plasmid presence, and antimicrobial susceptibility patterns. Of the nine Indonesian isolates, three were of capsular type A (A:1,3,13; A:1,3; and A:8). One isolate was of type B:2,3 and one isolate was of capsular type F. For three isolates, the capsular serogroup could not be identified. Plasmids the size of 2.3 kbp were present in three of the field isolates and two of the vaccine strains. One plasmid less than 2 kbp was isolated from the vaccine strain PM-V4. Eight distinct DNA profiles were obtained from digestion with the restriction endonuclease EcoRI, and seven distinct DNA profiles were obtained from digestion with the restriction endonuclease HindIII. All of the isolates were resistant to lincomycin and sulfadiazine and were susceptible to ampicillin and trimethoprim. Of the nine isolates, seven (78%) were susceptible to doxycycline and gentamicin and six (67%) were susceptible to enrofloxacin.     

Evaluation of Pasteurella multocida isolated from rabbits by capsular typing, somatic serotyping, and restriction endonuclease analysis.

The goal of this study was to characterize Pasteurella multocida isolated from rabbits. Five hundred and fifty-three apparently healthy rabbits were sampled for this study. Nasal swabs were collected from each rabbit for P. multocida isolation and identification. Isolates were further characterized by capsular and somatic antigens and genomic DNA fingerprinting. Thirty-nine P. multocida isolates were recovered from 553 rabbits (7%). Capsular typing was done by depolymerization of P. multocida capsule by Staphylococcus aureus hyaluronidase and by disc diffusion with mucopolysaccharidase enzymes (heparinase III, chondroitinase AC, and hyaluronidase). Thirty-one (79%) of the isolates were capsular type A, and 8 isolates (21%) had untypable (UT) capsules. The gel-diffusion precipitin test was used to determine the somatic type of P. multocida isolates. Nineteen isolates were somatic serotype 3 (49%), 12 were serotype 1 (31%), 1 was serotype 2, 2 were serotype 5, 2 were serotype 12 with a weak reaction to antiserum raised against serotype 7 (5%), and 1 was serotype 4. Two of the isolates (5%) were UT. Restriction endonuclease analysis of the DNA of the isolates revealed 7 distinct profiles by digestion with HindIII, and 12 profiles were obtained with HpaII, whereas digestion with EcoRI did not differentiate between any of the P. multocida DNA isolates studied. The DNA restriction endonuclease enzyme HpaII was found more useful for differentiating between DNA fingerprints of P. multocida rabbit isolates. However, no correlation between capsular type, somatic serotypes, and DNA fingerprints was seen in this study.     

Capsular serogroups of Pasteurella multocida isolated from animals in Zimbabwe

Pasteurella multocida is isolated from a variety of disease conditions from different animal species in our diagnostic laboratory. In order to determine serogroup distribution among the isolates, an indirect haemagglutination test using glutaraldehyde-fixed sheep red blood cells was employed. A serological examination of 79 isolates revealed that 47/79 were of capsular serogroup A, 11/79 capsular serogroup D, 4/79 capsular serogroup B and 17/79 were untypable strains. None of the isolates belonged to either serogroup E or F. All those from cases of classical pasteurellosis could be grouped, but a significantly high proportion of those which originated from companion animals were untypable. The significance of these results is discussed. This report appears to be the first detailed information on the prevalence of various serogroups of P. multocida in animals in southern Africa.     

Ribotype diversity of porcine Pasteurella multocida from Australia

OBJECTIVE: To use the technique of ribotyping to investigate the genetic diversity of Australian isolates of Pasteurella multocida associated with outbreaks of clinical disease in Australian pigs. DESIGN: One hundred and seven porcine P multocida isolates were analysed by ribotyping using the restriction enzymes HpaII and HindIII. The genetic population structure of the Australian porcine P multocida isolates was determined through statistical analysis of the joint ribotype patterns, and this was then compared with biochemical and epidemiological data available for the population. RESULTS: A total of 25 combined ribotypes were recognised, which were grouped into five ribotype clusters. Despite the deliberate selection of diverse isolates, the study revealed only a limited degree of genetic diversity. Fourteen of the ribotypes contained multiple isolates, and 12 of these ribotypes were present on more than one farm. Three of the seven biovars analysed in the study showed very limited diversity. All fifteen biovar 2 isolates (subsp multocida) were found in a single cluster (III), while all four biovar 8 isolates, which correspond to P multocida subsp gallicida, were allocated by themselves to a single cluster (IV). All nine of the biovar 12 isolates (lactose-positive subsp multocida) were assigned to a single cluster (I), together with the single biovar 14 isolate, which was the only other lactose-positive isolate in the population (ODC-negative). CONCLUSION: A limited number of ribotypes of P multocida are associated with Australian pigs. The majority of these ribotypes are widely distributed across multiple farms, and across multiple states. Individual farms can possess multiple ribotypes of P multocida. Some of the unusual biochemical variants of P multocida present in Australian pigs have a very limited genetic diversity. The nature of pig production in Australia, primarily involving continuous flow systems with few closed herds, has possibly contributed to the widespread distribution of a limited number ribotypes.     

Toxin types of Clostridium perfringens isolated from free-ranging,semi-domesticated reindeer in Norway

Samples of faeces were taken from 166 healthy domesticated reindeer (Rangifer tarandus tarandus) from three flocks in different reindeer husbandry districts in northern Norway and examined bacteriologically for the presence of Clostridium perfringens. The organism was isolated from 98 (59 per cent) of the reindeer. The isolates were classified into C perfringens toxin types by PCR analysis specific for the genes encoding the four major toxins (alpha, beta, epsilon and tau) and were subclassified by the detection of the genes encoding C perfringens beta2-toxin and enterotoxin. All the isolates belonged to C perfringens toxin type A. In addition, 15 of the 98 isolates were PCR-positive for the beta2-toxin gene, and two of the isolates had the the gene encoding for enterotoxin.     

Random amplification of polymorphic DNA and phenotypic typing of Zimbabwean isolates of Pasteurella multocida

Eighty-one isolates presumptively identified as Pasteurella multocida from a variety of diseases in animals in Zimbabwe were subjected to biochemical characterization, capsular typing and RAPD analysis. The majority of isolates (over 80%) were assigned into named taxa and were predominantly P. multocida subsp. multocida and P. multocida subsp. septica, whilst the remainder were unassigned. Serogroup A was predominant among the three capsular types (A, B and D) of P. multocida detected. Three main RAPD clusters and three subclusters were observed among the majority of isolates (93.8%), whilst the remainder was found to be weakly related. Nine different groups of strains with similar RAPD profiles (100% similarity) were also observed. The reference strain of capsular serogroup F clustered with the reference strain of P. multocida subsp. septica, whilst all other serogroups clustered with reference strains of subsp. multocida and gallicida. Notably, serogroups A and D were observed to be closely related to the reference strain of subsp. multocida. The relationship between biotype, capsular type, host origin and disease manifestation was not clear-cut. However, most pig isolates of subsp. multocida clustered together as did most cattle isolates of subsp. multocida. RAPD tended to separate subsp. multocida from septica.     

牛源荚膜A型多杀性巴氏杆菌疫苗候选株的筛选及鉴定

为了筛选生长快、毒力强、免疫原性好、副反应小的牛源荚膜A型多杀性巴氏杆菌（Pasteurella multocida，Pm）灭活疫苗菌株，本试验选取6株来自不同地区致犊牛肺炎死亡的牛源荚膜A型多杀性巴氏杆菌分离株，测定了培养基生长曲线、小鼠毒力、菌体脂多糖（LPS）含量及各菌株灭活菌苗免疫小鼠和家兔后的抗体效价，并进行了攻毒保护试验。结果显示，分离株Pm2、Pm3、Pm5生长速度较快、毒力较强、LPS含量较多，均含有与毒力和免疫相关的ptfA和fimA基因；免疫小鼠及家兔未发现明显不良反应，在二免后14 d血清抗体达1：64~1：128，强毒攻毒后全部存活，而PBS对照组全部死亡。本试验结果表明，Pm2、Pm3、Pm5均可作为多杀性巴氏杆菌灭活菌苗的候选菌株，其中Pm3作为首选株。     

Mycoplasmas and acholeplasmas isolated from ducks and their possible association with pasteurellas

Two hundred and sixty-three cases of clinically diseased ducks of all ages were examined for the presence of mycoplasmas. Mycoplasmas and acholeplasmas belonging to more than eight serogroups were cultured from 68 of them, and comprised 12 M anatis, one M columbinasale, two M gallinaceum, two M gallinarum, nine M synoviae, three unidentified Mycoplasma species, 37 Acholeplasma laidlawii and one unclassified acholeplasma belonging to each of serogroups 7 and 8. They were identified by biochemical characterisation, disc growth inhibition and agar gel diffusion tests. Fifty-three (78 per cent) of the isolates occurred with species of Pasteurella: 33.8 per cent with Pasteurella anatipestifer, 32.4 per cent with P multocida and 11.8 per cent with both P anatipestifer and P multocida. Nine of the isolates (13.2 per cent) were in pure culture and six (8.8 per cent) with other agents. Of the ducks negative for mycoplasmas 33.3 per cent were infected with P anatipestifer, 25.1 per cent with P multocida and 14.4 per cent with both P anatipestifer and P multocida. There was no correlation between the infections with mycoplasmas and P anatipestifer but there was a weak association between the infections with mycoplasmas, especially M anatis and P multocida.