Biochemical and serological properties of Actinobacillus pleuropneumoniae biotype 2 strains isolated from swine

The biochemical and serological properties of 21 strains of Actinobacillus pleuropneumoniae biotype 2 isolated from haemorrhagic necrotic pleuropneumonia of swine were examined. For serologic typing, the indirect haemagglutination (IHA) and the double gel-diffusion tests were used. On the basis of their soluble surface antigens, our A. pleuropneumoniae biotype 2 isolates could be assigned to two proposed serotypes. Serotype 1 comprised 11 strains and serotype 2 comprised 10 strains. All strains contained two surface antigen components. In the strains belonging to serotype 1, one of the antigens was identical with the serotype-specific antigen of Pasteurella haemolytica T4. Both antigens of serotype 2 strains proved to be type-specific. Four strains received from Switzerland, including the holotype strain of A. pleuropneumoniae biotype 2, and three strains isolated from swine in the G.D.R. belonged to serotype 2. Both the double gel diffusion and the IHA tests detected a 2-way cross-reaction between biotype 1, serotype 2 and biotype 2, serotype 2 strains of A. pleuropneumoniae, which could be eliminated using cross-absorbed sera.     

Serological characterization of Actinobacillus pleuropneumoniae serotype 2 strains by using polyclonal and monoclonal antibodies

The antigenic differences between strains of serotype 2 of both biotypes I and II of Actinobacillus pleuropneumoniae were studied by using several serological techniques. Monoclonal antibodies (MAbs) against A. pleuropneumoniae biotype I serotype 2 were produced by fusion of spleen cells of BALb/c mice immunized with whole-cell (WC) suspension with SP2/O-Ag14 murine myeloma cells. Desirable MAbs were selected by enzyme-linked immunosorbent assay (ELISA) using WC as antigen. MAbs MK-7 and MK-10 identified multiple bands of lipopolysaccharide in Western-blot. Treatment of WC with proteinase K and sodium periodate indicated that both MAb binding sites were carbohydrates in nature. In both ELISA and Western-blot, MAbs MK-7 and MK-10 recognized only biotype I serotype 2 isolates. Neither MAb MK-7 nor MK-10 reacted with reference strains of remaining serotypes of A. pleuropneumoniae and other Gram-negative bacteria tested. The results obtained with various serological tests showed that strains of serotype 2 biotype I shared antigenic determinants with strain N-282 of serotype 2 biotype II, but not with strain N-273 of serotype 1 biotype II. It is suggested that data obtained from this study may be helpful in the development of specific serotyping and serodiagnostic reagents of A. pleuropneumoniae strains.     

Analysis of occurrence of virulence genes among Yersinia enterocolitica isolates belonging to different biotypes and serotypes

The 150 Y enterocolitica strains isolated from humans and from pigs belonged to biotypes 4 (68.7%), 1A (18.7%) and 2 (4%), or were biochemically untypeable (8.6%). Biotype 4 was comprised of Y. enterocolitica strains representing serotype O:3, within biotype 1A the strains either belonged to serotypes O:5 and O:6 or were untypeable, and biotype 2 was represented by the strains of serotype O:9. The strains which were biochemically untypeable belonged to serotypes O:5, O:6 and O:3. Among the strains tested there also were those of an unidentified biotype and serotype. Nearly all the strains of biotype 1A represented genotype ystB+myfA+, and few belonged to genotype ystB+. The presence of the ystB gene in the strains of biotype 1A and only occasional occurrence of the gene in the other biotypes makes ystB a distinguishing marker of biotype 1A. The strains of genotype ystA+ail+myfA+yadA+ predominated in biotype 4 (serotype O:3). The strains of biotype 2 (serotype O:9) represented genotype ystA+ail+myfA+, and the plasmid yadA gene was detected in some of them. Within the group of biochemically untypeable strains ystB- and myfA-specific PCR products were mainly obtained. The genotypes determined for the tested biotypes and serotypes of Y. enterocolitica, based upon the selected genes of virulence, can be applied as distinguishing markers and indicators of the potential virulence of Y. enterocolitica strains, excluding bioserotyping.     

Competitive exclusion of Yersinia enterocolitica biotype 4, serotype O:3 by Yersinia enterocolitica biotype 1A, serotype O:6,30 in tissue culture and in pigs

AIMS: To study the adhesion properties of a biotype 4, serotype O:3 (human pathogenic) strain of Yersinia enterocolitica and to determine if adhesion in vitro and colonisation in vivo can be prevented by competition with a biotype 1A, serotype O:6,30 (non-pathogenic) strain. To study interaction between Y. enterocolitica biotype 4, serotype O:3 and cultured epithelial cells using the synthetic tripeptide arginine-glycine-aspartic acid (RGD). METHODS: The human intestinal epithelial (HEp-2) cell line was used for in vitro studies. Inocula of Y. enterocolitica biotype 4, serotype O:3 radiolabelled using tritium were incubated with HEp-2 cells and RGD tripeptide, or with Y. enterocolitica biotype 1A, serotype O:6,30 sequentially or concurrently, then washed and lysed, and radioactivity measured to determine the effect of RGD on adhesion, and competitive exclusion of pathogenic by non-pathogenic bacteria. For in vivo studies, two groups of 5-week-old piglets (n=5/group) were sequentially inoculated orally with 5 x 10(9) colony forming units (cfu) of either a non-pathogenic biotype 1A, serotype O:6,30 strain of Y. enterocolitica followed by a pathogenic biotype 4, serotype O:3 strain, or vice versa. Pigs were monitored for carriage of strains using bacterial culture and a multiplex polymerase chain reaction (PCR). RESULTS: The RGD tripeptide significantly inhibited adherence of the pathogenic Y. enterocolitica strain to cultured epithelial cells, suggesting that adhesion involved the RGD tripeptide sequence. The non-pathogenic biotype 1A, serotype O:6,30 strain of Y. enterocolitica prevented adhesion of the pathogenic strain to cells in vitro when allowed to adhere first. Pathogenic Y. enterocolitica was consistently isolated from rectal swabs from 80-100% of pigs on all sampling occasions but not from oral swabs after 14 days in pigs first inoculated with the non-pathogenic strain or at 26 days in pigs first inoculated with the pathogenic strain. CONCLUSIONS: A non-pathogenic strain of Y. enterocolitica reduced adhesion of a human pathogenic strain in vitro but not in vivo.     

Evaluation and application of ribotyping for epidemiological studies of Actinobacillus pleuropneumoniae in Denmark

The aim of the present study was to evaluate ribotyping as an epidemiological tool for Actinobacillus pleuropneumoniae and apply the method in studies of A. pleuropneumoniae infections in Danish pig herds. The evaluation of ribotyping was based on the 13 international reference strains and 106 epidemiologically unrelated Danish field strains representing the nine serotypes of biotype 1 (1, 2, 5A/B, 6, 7, 8, 10, 12, and K2:O7) and one serotype 14 of biotype 2. Enzymes CfoI and HindIII were chosen for generation of ribotype patterns. Ribotyping of the reference strains resulted in 10 CfoI types and 11 HindIII types. Ribotyping of the Danish strains resulted in 17 different CfoI ribotypes and 24 different HindIII ribotypes. Combining HindIII- and CfoI-ribotyping divided the Danish strains into 26 different types. The stability, reproducibility and typability of ribotype patterns were good, and the discriminatory power was between 0.85–0.89. The relatively low discriminatory power was caused by four predominant types, containing 61% of the isolates. The typing system was applied in studies of routes of infection of specific pathogen-free (SPF) pig herds and included 112 strains of A. pleuropneumoniae. Airborne transmission from neighboring conventional pig farms was investigated in 12 cases of infected SPF herds. Transmission via vehicles transporting pigs between SPF herds was investigated in nine cases while transmission by trading of pigs between SPF herds was investigated in two cases. Serotype 2 was isolated from all SPF herds included in this study, except one, emphasizing the high prevalence of this serotype in Denmark. By ribotyping, airborne transmission was indicated in five of 12 cases, transmission via pig transporting vehicle was indicated in six of nine cases, and transmission via trading was indicated in one of two cases. In many cases findings of predominant ribotypes made interpretations of suspected routes of transmission difficult. The relationship of strains based on ribotypes was calculated using Dices coefficient and clustered by UPGMA. HindIII ribotypes of serotype 2 strains were closely related, though only showing 43% similarity to HindIII ribotypes of remaining serotypes.     

Competitive exclusion of Yersinia enterocolitica biotype 4, serotype O:3 by Yersinia enterocolitica biotype 1A,serotype O:6,30 in tissue culture and in pigs

AIMS: To study the adhesion properties of a biotype 4, serotype O:3 (human pathogenic) strain of Yersinia enterocolitica and to determine if adhesion in vitro and colonisation in vivo can be prevented by competition with a biotype 1A, serotype O:6,30 (non-pathogenic) strain. To study interaction between Y. enterocolitica biotype 4, serotype O:3 and cultured epithelial cells using the synthetic tripeptide arginine-glycine-aspartic acid (RGD).

METHODS: The human intestinal epithelial (HEp-2) cell line was used for in vitro studies. Inocula of Y. enterocolitica biotype 4, serotype O:3 radiolabelled using tritium were incubated with HEp-2 cells and RGD tripeptide, or with Y. enterocolitica biotype 1A, serotype O:6,30 sequentially or concurrently, then washed and lysed, and radioactivity measured to determine the effect of RGD on adhesion, and competitive exclusion of pathogenic by non-pathogenic bacteria. For in vivo studies, two groups of 5-week-old piglets (n=5/group) were sequentially inoculated orally with 5x10⁹ colony forming units (cfu) of either a non-pathogenic biotype 1A, serotype O:6,30 strain of Y. enterocolitica followed by a pathogenic biotype 4, serotype O:3 strain, or vice versa. Pigs were monitored for carriage of strains using bacterial culture and a multiplex polymerase chain reaction (PCR).

RESULTS: The RGD tripeptide significantly inhibited adherence of the pathogenic Y. enterocolitica strain to cultured epithelial cells, suggesting that adhesion involved the RGD tripeptide sequence. The non-pathogenic biotype 1A, serotype O:6,30 strain of Y. enterocolitica prevented adhesion of the pathogenic strain to cells in vitro when allowed to adhere first. Pathogenic Y. enterocolitica was consistently isolated from rectal swabs from 80-100% of pigs on all sampling occasions but not from oral swabs after 14 days in pigs first inoculated with the non- pathogenic strain or at 26 days in pigs first inoculated with the pathogenic strain.

CONCLUSIONS: A non-pathogenic strain of Y. enterocolitica reduced adhesion of a human pathogenic strain in vitro but not in vivo.     

Evaluation of an indirect enzyme-linked immunosorbent assay (ELISA) for detection of antibodies to the Apx toxins of Actinobacillus pleuropneumoniae

The reference strains of the 12 serotypes of Actinobacillus pleuropneumoniae express one or two of three different RTX exotoxins designated Apx I, Apx II and Apx III. The toxins are important virulence factors. In the present study, ELISAs with purified Apx I, Apx II and Apx III, respectively, as antigen were evaluated as candidates for serological diagnosis of Actinobacillus pleuropneumoniae infection in pigs. The pigs were inoculated with biotype 1, serotypes 1-12, and biotype 2, serotype 14, respectively. A strong humoral antibody response was seen to all the three antigens in most pigs irrespective of the serotype used for inoculation. However, titers to the exotoxins secreted by the serotype used for inoculation were generally highest. The results show that toxin proteins of Actinobacillus pleuropneumoniae are antigenically related and that a correlation between serotype and secretion of exotoxin is not revealed serologically in the ELISA test.     

Evaluation of an enzyme-linked immunosorbent assay for serological surveillance of infection with Actinobacillus pleuropneumoniae serotype 5 in pig herds

An indirect enzyme-linked immunoassay for serological surveillance of infection of pigs with Actinobacillus pleuropneumoniae (Ap) serotype 5 was developed. The antigen used was prepared from Ap serotype 5b strain L20. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that the antigen contained high molecular weight lipopolysaccharide (LPS) and presumably also capsular polysaccharide (CP). The Ap serotype 5 ELISA was tested using sera from pigs experimentally infected with the 12 different Ap serotypes of biotype 1 and with sera from herds naturally infected with Ap serotypes 5, 6, 7 and 12. Cross-reactions were shown in one pig from a herd naturally infected with Ap serotype 7 and in one pig from a herd naturally infected with Ap serotype 12. The herd sensitivities of the Ap5 ELISA and a complement fixation test (CFT) were both estimated to 1.0, on the basis of serum samples from six herds naturally infected with Ap serotype 5. The herd specificities of both tests were estimated to 0.98, based on serum samples from 123 pig herds (10 samples from each herd) from the Danish specific pathogen-free (SPF) programme for pig production.     

Phenotyping of E. coli serotypes associated to oedema disease

Background

Oedema disease is a severe disease, mainly affecting recently weaned pigs. It is caused by E. coli strains that express fimbriae F18 and produce verotoxin 2e, mainly belonging to serotype O138, O139 or O141. The aim of this study was to compare E. coli isolates within these serotypes with respect to diversity.

Methods

Faecal E. coli strains belonging to serotypes O138, O139 and O141 isolated during the period 1994–1998 from Swedish pigs aged less than 12 weeks were compared using a biochemical fingerprinting system. Aiming to compare the results obtained over time, also strains isolated during 1964–67 and 1975–80 were included in the study. The study comprised 129, 263 and 95 isolates of E. coli serotype O138, O139 and O141, respectively.

Results

Biochemical phenotypes (BPTs) were defined. At each sampling occasion each herd could only contribute with one isolate per BPT. Consequently, all but one of identical BPTs identified at a specific sampling occasion was omitted. The final number of isolates from 1994–98 that was compared included 64, 182 and 41 isolates of serotypes O138, O139 and O141, respectively. Within each serotype, the dominating BPT included over 65% of the compared isolates, demonstrating a large dominance of one BPT per serotype. These dominating BPTs were also demonstrated in the material from the 1960ies and the 1970ies. Still, the presence of other common BPTs (especially within serotype O138 and O139) demonstrated a certain variation within serotype. In a herd severely affected by oedema disease, E. coli serotype O139 was easily demonstrated in diseased pigs but only rarely in apparently healthy weaners

Conclusion

The results obtained demonstrate the presence of dominating BPTs within the oedema disease inducing serotypes. A stability of these BPTs over time was observed, presumably at least partly due to a never-ending access to naïve pigs. Still, the presence of other common BPTs indicates a variation over time, which visualises the importance of monitoring for this. Such studies should focus on pigs affected by oedema disease, because oedema disease inducing strains of E. coli were only rarely demonstrated in healthy pigs in a herd affected by oedema disease.     

Occurrence of virulence markers in species of Yersinia isolated from animals in Nigeria

Fourteen strains of Yersinia species isolated from apparently healthy pigs and cattle in Nigeria were screened for four virulence markers using six test systems. These were two in vitro assays, namely, calcium dependency and autoagglutination, both at 37 degrees C, the Serény test in guinea-pigs and the detection of heat-stable enterotoxin (ST) by the rabbit ileal loop test, the ligated intestine test in pigs and the infant mouse system. Seven of the 14 strains of Yersinia were positive for one or more of these tests. Six of nine strains of Y. enterocolitica and one of four Y. intermedia were positive in one or more tests. The only strain of Y. frederiksenii isolated was negative in all six test systems. All three strains of Y. enterocolitica, serotype 0:8 and the only serotype 0:3 isolated were positive in one or more tests. However, only two of five strains of Y. enterocolitica serotype 0:12, 26, the most frequently encountered, were positive. A good correlation was observed between test results of calcium dependency, autoagglutination and Serény assays. The results indicate that cattle and pigs have the potential to transmit virulent strains of Y. enterocolitica to human beings in Nigeria.     

Characterization of Pasteurella haemolytica strains isolated from goats in Hungary

Thirty-five Pasteurella haemolytica strains were isolated in Hungary from goat carcasses sent for postmortem examination from two farms with large goat flocks. All strains belonged to biotype A and with the exception of one strain of serotype A8 they belonged to serotype A2. No untypable strains were found by the indirect haemagglutination test.     

Serotype and apx genotype profiles of Actinobacillus pleuropneumoniae field isolates in Korea.

A total of 100 field isolates of Actinobacillus pleuropneumoniae isolated from lung tissues of pigs with severe pleuropneumonia were serotyped by slide agglutination and precipitation tests. Polymerase chain reactions for apxICA, apxIICA, apxIIICA, apxIBD and apxIIIBD genes were used to determine their genotype prevalence. Serotypes 2 (56 isolates), 5 (28 isolates) and 6 (11 isolates) were the most common; only two isolates belonged to serotype 7, and three were untyped. Among the 97 isolates identified by serotype, 70 had the same apx genes as their respective serotype reference strains, but 27 did not have any of the apx genes present in the corresponding serotype reference strain. Among these 27 isolates, 10 were serotype 2, 12 were serotype 5, three were serotype 6 and two were serotype 7.     

Clonal distribution of Streptococcus suis isolated from diseased pigs in the central region of Chile

The characteristics of 29 Chilean field strains of Streptococcus suis recovered between 2007 and 2011 from pigs with clinical signs at different farms were studied. Serotyping with use of the coagglutination test revealed that all but 1 strain belonged to serotype 6; the remaining strain was serotype 22. All the serotype-6 strains were suilysin (hemolysin)-negative; in addition, they were found to be genotypically homogeneous by enterobacterial repetitive intergenic consensus sequence-based polymerase chain reaction (ERIC-PCR) and sensitive to ampicillin, ceftiofur, penicillin, and trimethoprim/sulfamethoxazole. The results indicate that, in contrast to what is generally observed in other countries, a single clone of S. suis was isolated from diseased pigs in the central region of Chile.     

SEROLOGICAL CLASSIFICATION OF AUSTRALIAN STRAINS OF ERYSIPELOTHRIX RHUSIOPATHIAE ISOLATED FROM PIGS, SHEEP, TURKEYS AND MAN

154 strains of Erysipelothrix rhusiopathiae from pigs, sheep, turkeys and man were serotyped by using the double diffusion gel precipitation test. Ten of the 18 serotypes were detected in 151 of the strains. Three strains failed to react with any of the type specific antisera. It was found that serotype 1a shared an antigen(s) with serotype 1b, and that serotype 6 shared an antigen(s) with serotype 14. Serotype 2a and 2b were difficult to distinguish. Since serotypes 1 and 2 were isolated from cases of septicaemia in pigs, and since serotypes 1, 2, 4 and 7 were isolated from cases of arthritis, it was suggested that factors other than serotype were important in causing the various forms of swine erysipelas. The fact that the distribution of serotypes 1a, 1b and 2b between septicaemic and arthritic pigs was similar supported the conclusion that arthritis was consequent to bacteraemia. Serotypes 1a, 1b, 2b, 5, 12 and 15 were isolated from cases of arthritis in sheep, and serotypes 1a and 5 from cases of erysipelas in turkeys. Serotype 2b was isolated from a human specimen.     

Comparison of sampling and isolation procedures for recovery of Yersinia enterocolitica serotype O:3 from the oral cavity of slaughter pigs

Yersinia enterocolitica serotype 0:3/biotype 4 was isolated from the oral cavity of altogether 32 (68.1 %) of 47 freshly eviscerated slaughter pigs. Most efficient recovery was achieved by cultivation of tissue samples from both tongue and tonsils of the same individual. The isolation rate so obtained was significantly higher than that obtained by separate examination of either tonsil swabs or tongue swabs. However, the isolation frequency achieved by combined swabbing of the 2 sites was not significantly different. In general, tonsils were more productive for the recovery of 0:3 strains than were tongues, and tissue samples yielded higher isolation rates than did swabs. Three-week cold enrichment in a low selective medium proved essential for optimal recovery. However, the highest number of isolates was obtained using a combination of methods, including direct plating and selective enrichment in a modified Rappaport broth in addition to cold enrichment.     

Comparative virulence of some English strains of Haemophilus pleuropneumoniae serotypes 2 and 3 in the pig

Between 10(7.5) and 10(8.1) viable organisms of four English and one Danish strain of Haemophilus pleuropneumoniae serotype 2 and five English strains of serotype 3 were inoculated intranasally into groups of conventional pigs. Among the English isolates of both serotypes there were virulent and non-virulent strains. Four of the serotype 2 strains, including the Danish strain, and two of the serotype 3 strains produced varying degrees of pulmonary consolidation with abscess formation and pleurisy in at least three of the five pigs in the individual groups. H pleuropneumoniae was isolated from the pulmonary lesions in all save one instance, frequently from the tonsil but less frequently from other parts of the respiratory tract. Purulent arthritis and tenosynovitis developed in one animal infected with serotype 3. Apart from the latter pig no clinical signs of illness were detected except for febrile reactions which reflected the prevalence of the thoracic lesions in the various groups. A humoral antibody response was detected by indirect immunofluorescence in two-thirds of the pigs which developed lesions but in fewer by complement fixation.     

Development and evaluation of a mixed long-chain lipopolysaccharide based ELISA for serological surveillance of infection with Actinobacillus pleuropneumoniae serotypes 2, 6 and 12 in pig herds

The objective was to develop an enzyme-linked immunosorbent assay (ELISA) for simultaneous detection of antibodies against Actinobacillus pleuropneumoniae (Ap) serotypes 2, 6 and 12. The assay was designated MIX-ELISA. Lipopolysaccharide (LPS) from Ap serotypes 2, 6 and 12 was purified using hot phenol-water extraction followed by fractionation by size-exclusion chromatography. A mixture of fractions containing molecules with molecular weight above 50 kDa from all three serotypes was used as antigen. The MIX-ELISA was evaluated with sera from pigs experimentally infected with the serotypes 1, 2, 5b, 6, 7, 8, 10 and 12 of Ap biotype 1. In addition to reaction with sera from pigs inoculated with Ap serotypes 2, 6 and 12, reaction was observed with sera from pigs inoculated with serotype 8. Furthermore, the sensitivity and specificity of the test on a herd level were evaluated with sera from herds naturally infected with serotypes 2, 6 or 12 and with sera from herds free of infection with any Ap serotype of biotype 1. The ELISA showed a high herd sensitivity (0.98; 95% confidence interval: 0.89-1.00) and specificity (0.95; 0.88-0.99). The high diagnostic sensitivity and specificity of the assay indicate that screening of herds for Ap infection can be performed using this ELISA. Efficient serological surveillance can be achieved by using such mixed antigen ELISAs coated with size-selected LPS-antigens from the most prevalent serotypes.     

Genomic relatedness among Actinobacillus pleuropneumoniae field strains of sterotypes 1 and 5 isolated from healthy and diseased pigs.

Forty-four Actinobacillus pleuropneumoniae isolates recovered from both healthy and diseased pigs were characterized by random amplified polymorphic DNA analysis (RAPD), pulsed field gel electrophoresis (PFGE) and apx toxin gene typing. Nine RAPD types and 14 PFGE patterns were identified. No common RAPD or PFGE patterns were found between strains of serotype 1 and those of serotype 5. The RAPD analysis indicated that the 15 serotype 1 strains isolated from diseased pigs were assigned to 4 RAPD types, with 66% of strains characterized by the same RAPD type. By contrast, the 5 strains of serotype 1 isolated from healthy carriers were dispersed in 4 RAPD types. These data suggest that the diversity of strains isolated from healthy pigs could be higher than that of strains recovered from diseased pigs. In addition, all serotype 5 strains exhibited a unique RAPD type. Unlike RAPD, PFGE analysis allowed discrimination among isolates of serotype 1 and among those of serotype 5. All but 3 isolates showed the same apx genotype as their respective serotype reference strain. These data indicate that RAPD analysis is a valuable rapid tool for routine subtyping of strains of serotype 1. For strains of serotype 5, a combination of several typing methods, such as PFGE and apx gene typing, is needed to provide useful information on the molecular epidemiology of swine pleuropneumonia.     

Severe pleuritis associated with certain strains of Pasteurella multocida in swine

Pasteurella multocida was isolated from 2 farms on which grower or finisher pigs had problems of severe emaciation and high death loss (greater than 5%). At necropsy, the pigs had extensive suppurative pleuritis and pericarditis, with adhesions over the lung surface. On one farm, the pigs also had multiple lung abscesses. Histologic findings included polymorphonuclear cell infiltration in bronchial and alveolar spaces, thickening of alveolar walls, pleuritis, and in some cases, abscesses. From all pigs, P multocida was isolated. The strains (A52, A59) were serotype A and were nontoxigenic. Experimental reproduction of the disease was achieved by sequentially infecting conventionally weaned pigs intranasally with pseudorabies virus; 7 days later, infection with selected P multocida laboratory strains (A50 and D82, A52 and A59) was achieved. At necropsy, pigs inoculated with strains A59 and A52 (serotype A, pleurotropic) had more severe lesions (P less than 0.05) than those inoculated with strain A50 (serotype A, pneumotropic). Also, pigs infected with strains A59 and A52 had extensive pleuritis and abscessation, which were not observed in the other groups. Strain D82 (serotype D) was not capable of producing pneumonia or pleuritis. Pleuritis and abscessation may be associated with certain P multocida strains that are serotype A, but not with others. These pleurotropic strains seem to be more virulent than pneumotropic strains, and infection with the former may result in extensive pleuritis and abscess formation.     

Characteristics of Haemophilus pleuropneumoniae Isolates and Some Epidemiological Findings on Porcine Haemophilus Pleuropneumonia in Saskatchewan

Thirty isolates of Haemophilus pleuropneumoniae from clinical and slautherhouse cases of porcine Haemophilus pleuropneumonia in Saskatchewan as well as six isolates from British Columbia and Ontario were subjected to cultural, biochemical, serological and antibiotic sensitivity tests. All strains were Gram-negative pleomorphic rods or coccobacilli which grew only in the presence of V factor and all produced porphyrin from delta-aminolaevulinic acid. Biochemically, the organism was positive for urease, O-nitrophenyl-β-D-galactopyranosidase and the fermentation of sucrose, mannitol, dextrose, lactose and xylose, but was usually negative for indole. Most strains of H. pleuropneumoniae were sensitive to chloramphenicol, furamazone, carbenicillin and ampicillin, but only about 50% were sensitive to tetracycline. Serotype 5 was more common than serotype 1 or the untyped strains among Saskatchewan isolates. In addition, serotype 3 was identified from British Columbia.

Retrospective epidemiological studies showed that Haemophilus pleuropneumonia occurred and recurred on farms in the Saskatoon and adjoining districts, serviced by the diagnostic laboratories of the Western College of Veterinary Medicine and that the disease was more common among three month old pigs during the fall-winter season.