# Occurrence of Multiple stx1 Genes and Rare Genomic Variation in stx1 Shiga Toxin-Producing Escherichia coli

## TL;DR

This study reports the occurrence of multiple stx1 genes and rare genomic variations in Shiga toxin-producing E. coli, which could affect diagnostic accuracy and disease severity.

## Contribution

The study identifies rare genomic variations and multiple stx1 gene occurrences in STEC strains, previously underreported.

## Key findings

- Two STEC strains showed genomic variations in the stx1 operon, including multiple stx1 genes.
- Public genome data revealed additional strains with multiple stx1 genes, suggesting relevance to human infections.
- Current diagnostic methods may miss multiple stx1 genes of the same subtype.

## 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.