Analysis of stx gene variants and putative adhesin genes of non-O157 Shiga toxin-producing Escherichia coli isolates

Objective To understand the stx gene variants and putative adhesin genes of the non-O157 Shiga toxin-producing Escherichia coli (STEC) isolates collected from some areas in China. Methods Polymerase chain reaction (PCR) was performed to amplify the complete stx1 and stx2 genes of 29 non-O157 STEC isolates, and PCR products were sequenced and compared with the published sequences of stx1 and stx2 variants in the GenBank. Genes of pathogenicity island called locus of enterocyte effacement (LEE) and other putative adhesin genes outside the LEE were also investigated by PCR. Results Among 25 stx1 positive isolates, 13 carried stx1a, 12 carried stx1c. Among 10 stx2 positive isolates, 7 carried stx2d, and stx2g, stx2a were identified from 1 isolate respectively, 1 isolate carried the stx2 variant that is similar to stx2e in A subunit and identical to stx2d in B subunit. Seven genes encoded in the LEE were all negative among 29 isolates; putative adhesin genes iha was identified in 26 isolates (89.7%); saa was detected in 3 isolates; eibG was detected in 1 isolate; other 6 putative adhesin genes were all negative. Conclusion The predominant stx variants of non-O157 STEC isolates from some areas in China were stx1c and stx2d, the absence of the 7 genes in the LEE suggested that the 29 isolates were all LEE negative. The putative adhesin gene iha was widely distributed while saa and eibG genes were present only in some isolates. The mechanisms that mediate colonization of non-O157 STEC strains are needed to be further studied.