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

Abstract

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 §ssub§ 1 §esub§ genes of nine STEC strains were located on large plasmids. The subAB §ssub§ 2 §esub§ allele (here designated subAB §ssub§2- 1§esub§), 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 §ssub§2§esub§ variant, designated subAB §ssub§2-2§esub§ 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 §ssub§2§esub§ variants. DNA analysis indicated sequence conservation in the plasmid-located alleles and sequence heterogeneity among the chromosomal subAB §ssub§ 2 §esub§ 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 §ssub§2-2§esub§ was described, which can occur in addition to subAB §ssub§2- 1§esub§ on a new chromosomal locus. © 2013 Funk et al.; licensee BioMed Central Ltd.