Subtilase Cytotoxin-Coding Genes in Verotoxin-Producing Escherichia coli Strains from Sheep and Goats Differ from Those from Cattle
ABSTRACTSubtilase cytotoxin (SubAB) from verotoxin (VT)-producingEscherichia coli(VTEC) strains was first described in the 98NK2 strain and has been associated with human disease. However, SubAB has recently been found in two VT-negativeE. colistrains (ED 591 and ED 32). SubAB is encoded by two closely linked, cotranscribed genes (subAandsubB). In this study, we investigated the presence ofsubABgenes in 52 VTEC strains isolated from cattle and 209 strains from small ruminants, using PCR. Most (91.9%) VTEC strains from sheep and goats and 25% of the strains from healthy cattle possessedsubABgenes. The presence ofsubABin a high percentage of the VTEC strains from small ruminants might increase the pathogenicity of these strains for human beings. Some differences in the results of PCRs and in the association with some virulence genes suggested the existence of different variants ofsubAB. We therefore sequenced thesubAgene in 12 strains and showed that thesubAgene in most of thesubAB-positive VTEC strains from cattle was almost identical (about 99%) to that in the 98NK2 strain, while thesubAgene in most of thesubAB-positive VTEC strains from small ruminants was almost identical to that in the ED 591 strain. We propose the termssubAB1to describe the SubAB-coding genes resembling that in the 98NK2 strain andsubAB2to describe those resembling that in the ED 591 strain.