TOXIN DETECTION IN Pasteurella multocida STRAINS ISOLATED FROM SWINE LUNGS IN THE STATE OF RIO GRANDE DO SUL, BRAZIL DETECÇÃO DA PRODUÇÃO DE TOXINA EM AMOSTRAS DE Pasteurella multocida ISOLADAS DE PULMÕES DE SUÍNOS NO RIO GRANDE DO SUL

Toxin production and the presence of the toxA gene was assayed in 24 Pasteurella multocida strains isolated from pigs with pneumonia and pleuritis in the State of Rio Grande do Sul, Brazil. Toxigenicity was assessed through a mouse lethality test and a PCR amplification assay was used to obtain a 300 bp product from the toxA gene. In order to demonstrate that the amplified product corresponded to the toxA gene, the same segment of a reference P. multocida capsular type D toxigenic strain was amplified and treated with the restriction enzyme Taq1, and the restriction fragments corresponded to the expected sizes. Only one out of 24 strains of P. multocida was toxigenic in the mouse lethality test. However, with the use of PCR, nine strains carried the toxA gene. Hypothesis to explain this difference is the suppression of genic expression in vivo or the presence of a defective, non-functional gene.