Detection of type III secretion system genes in animal isolates of Bordetella bronchiseptica

A cosmid clone bank of Bordetella bronchiseptica genomic DNA was screened f or the presence of type III secretion (TTS) genes using a probe derived fro m the TTS system genes of Ralstonia solanacearum. A 3.35 kb PstI fragment, sub-cloned from a hybridising cosmid clone, was sequenced and found to cont ain a 97 bp overlap with the previously reported B. bronchiseptica bscIJKLN O TTS gene cluster. DNA and predicted protein homology analysis suggests th at a bscPQRST cluster lies immediately downstream of bscIJKLNO. A PCR ampli fication assay indicated that the bscT locus was present in 27 B, bronchise ptica animal isolates tested (100%). Dot-blot DNA hybridisation using probe s for bscT and bscP confirmed the presence of these loci in six canine isol ates associated with a variety of clinical signs. Although TTS has been imp licated in the pathogenicity of B, bronchiseptica, it is likely that differ ent clinical manifestations may be due to variations in gene expression or host factors, rather than the absence or presence of TTS genes. (C) 2000 El sevier Science B.V. All rights reserved.