Phenotypic characterization of Pasteurella multocida strains isolated from pigs with broncho and pleuropneumonia

CAPPUCCIO J., ; LEOTTA G.A., ; VIGO G., ; MOREDO F., ; WOLCOTT M.J., ; PERFUMO C.J.

Hamburg, Germany

Congreso; 18th IPVS Congress; 2004

Pasteurella multocida is characterized in 5 groups by determination of their capsular type. In pigs, capsular type D is associated with progressive atrophic rhinitis and type A with pneumonic pasteurellosis or as secondary invaders of M. hyopneumoniae or A. pleuropneumoniae. OMP provide a classification in 16 somatic serotypes. Combination of both phenotypic tools yield that A:3; A:5; D:5 and D:3 are the most commonly found in pigs. The relationship between virulence factors of P. multocida type A and pneumonia, is contradictory because it has been associated exclusively with nontoxigenic strains (1) or with toxigenic ones (2). Capsule, adherence factors, endotoxins and proteins of slightly lower molecular mass than Apx toxins might paly an important role (1). Gross lesions are difficult to differentiate from those found in M. hyopneumoniae infection. Microscopically it is defined as lobular exudative bronchopneumonia (2). However, field observations showed that, besides the classical form, P. multocida could be isolated from cases of A. pleuropneumoniae like lesions (PnAp). The objective of this study was to identify phenotypically the isolates of P. multocida from lungs with bronchopneumonia PnAp-like lesions and to correlate them with the histopathological findings. Materials and methods Ten strains (1-10), isolated from 2000 to 2002 were examined. They were selected because the availability of pneumonic tissue. It belonged from 9 different intensive operations (A-I). In 3 of them (B, C, and F) A. pleuropneumoniae have been isolated. In 5 of them (A, B, C, G and I) PnAp-like lesions were observed. Phenotypic caracterization included the presence of oxidase, catalase, beta galactosidase, urease, indol production and to fermented carbohydrates. Capsular and somatic serotypes were carried out by multiplex PCR and agar gel precipitation test respectively. Lungs samples were fixed in 10% buffered formalin. Results All the isolates were identified as P. multocida subspecies multocida biovar 3. Four strains belonged to capsular and somatic type A:3, 4 strains D:3x5, 1 D:3 and 1 A:4. P. multocida D:3 or A:3 were isolated from both acute/chronic broncho or pleuropneumonic lesions from farms with or without A. pleuropneumoniae infection. Light microscopic changes found in PnAp-like lesions were indistinguishable from those produced by A. pleuropneumoniae. Discussion Several studies have shown that P. multocida type A is the predominant type found in pneumonic lesions (2). However in our study both types A and D were isolated. Besides, from farms free of A. pleuropneumoniae infection, both types of pneumonic lesions yield capsular types A and D as well as lungs with PnAp-like lesions from infected farms. Among the different somatic serotypes, P. multocida D:3,5 and A:3 was the most frequently isolated from lungs. The low number of P. multocida phenotyped and lungs examined warrants of further comments and conclusion. Research effort towards genotyping the isolates and experimental inoculation might provide additional information of the possible role of P. multocida on the pathogenic.