Molecular analysis of subtilase cytotoxin genes of food-borne Shiga toxin-producing Escherichia coli reveals a new allelic subAB variant

BACKGROUND: The open reading frames of subAB genes and their flanking regions of 18 food-borne Shiga toxin-producing E. coli (STEC) strains were analyzed. RESULTS: All but one subAB open reading frames (ORF) were complete in all STEC strains. The subAB(1) genes of nine STEC strains were located on large plasmids. The subAB(2) allele (here designated subAB(2-1)), which was recently described by others to be present in the Subtilase-Encoding PAI (SE-PAI) was found in 6 STEC strains. A new chromosomal subAB(2) variant, designated subAB(2-2) was detected in 6 strains and was linked to a chromosomal gene hypothetically encoding an outer membrane efflux protein (OEP). Three STEC strains contained both subAB(2) variants. DNA analysis indicated sequence conservation in the plasmid-located alleles and sequence heterogeneity among the chromosomal subAB(2) genes. CONCLUSIONS: The results of this study have shown that 18 subAB-PCR positive STEC strains contain complete subAB open reading frames. Furthermore, the new allelic variant subAB(2-2) was described, which can occur in addition to subAB(2-1) on a new chromosomal locus.