ACTINOBACILLUS SUIS STRAINS ISOLATED FROM HEALTHY AND DISEASED SWINE ARE CLONAL AND CARRY APXICABD(VAR. SUIS) AND APXIICA(VAR. SUIS) TOXIN GENES

Actinobacillus suis isolates recovered from both healthy and diseased pigs were characterized by biochemical testing, serotyping, restrictio n endonuclease fingerprinting, and apr toxin gene typing, The clinical isolates analyzed were collected over a 10-year period from approxima tely 40 different locations in southwestern Ontario, Canada. Little va riation in the biochemical profiles of these isolates was seen, and al l isolates reacted strongly with rabbit antisera prepared against one of the strains. Similarly, by using BamHI and BglII for restriction en donuclease fingerprinting (REF) analysis, all isolates were found to b elong to a single REF group. Minor variations could be detected, espec ially in the BglII fingerprints, but overall the patterns were remarka bly similar. Sequences that could be amplified by PCR with primers to the apxICA and apxIICA genes of Actinobacillus pleuropneumoniae were d etected in all strains. Although no amplification was obtained with pr imers to the A. pleuropneumoniae apxIBD genes, sequences with homology to apxIBD were detected by hybridization. There was no evidence of ap xIII homologs. Taken together, these data suggest that A. suis isolate s are genotypically and phenotypically very similar, regardless of the ir source, and that they contain genes similar to, but not identical t o, the apxICABD and apxIICA genes of A. pleuropneumoniae.