Occurrence of Multiple <i>stx1</i> Genes and Rare Genomic Variation in <i>stx1</i> Shiga Toxin-Producing <i>Escherichia coli</i>

Abstract

Shiga toxin-producing Escherichia coli are important foodborne pathogens. There are several subtypes of the Shiga toxin Stx known, with Stx2 (a–o) being more diverse than Stx1 (a, c, d). Multiple occurrences of stx2 genes as well as combinations of stx1 and stx2 have been reported. However, there is a lack of knowledge on the occurrence of multiple stx1 genes in STEC strains. Here, we report two strains from food and animal feces which show genomic variations in the stx1 operon. The first strain harbors stx1a and stx1c genes, and the second strain shows an inactive stx1 operon due to an insertion in the stxA1a subunit gene. The screening of publicly available complete genome sequences of STEC revealed further strains harboring multiple stx1 genes, indicating that those strains also occur in human infections. This should be kept in mind when applying routine diagnostic methods like PCR, that do not detect multiple occurrences of stx1 genes of the same subtype. Moreover, the impact on the severity of human infections due to multiple stx1 genes has not been investigated well.

Keywords

• <i>Escherichia coli</i>
• STEC
• stx
• genome