Abstract
Shiga Toxin-producing Escherichia coli (STEC) are a group of foodborne pathogens associated with diarrhea, dysentery, hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS). Shiga toxins are the major virulence factor of these pathogens, however adhesion and colonization to the human intestine is required for STEC pathogenesis. A subset of STEC strains carry the Locus of Enterocyte Effacement (LEE) pathogenicity island (PAI), which encodes genes that mediate the colonization of the human intestine. While LEE-positive STEC strains have traditionally been associated with human disease, the burden of disease caused by STEC strains that lacks LEE (LEE-negative) has increased recently in several countries; however, in the absence of LEE, the molecular pathogenic mechanisms by STEC strains are unknown. Here we report a 86-kb mosaic PAI composed of four modules that encode 80 genes, including novel and known virulence factors associated with adherence and autoaggregation. Therefore, we named this PAI as Locus of Adhesion and Autoaggregation (LAA). Phylogenomic analysis using whole-genome sequences of STEC strains available in the NCBI database indicates that LAA PAI is exclusively present in a subset of emerging LEE-negative STEC strains, including strains isolated from HC and HUS cases. We suggest that the acquisition of this PAI is a recent evolutionary event, which may contribute to the emergence of these STEC.
Highlights
Shiga Toxin-producing Escherichia coli (STEC) are a group of foodborne pathogens associated with gastrointestinal diseases, including acute diarrhea and dysentery
We identified a member of the Heat-resistant agglutinin family (Hra Family) produced by the Locus of Enterocyte Effacement (LEE)-negative O113:H21 STEC strain E045-00, which is seroreactive to sera from patients with HUS16
Our findings strongly suggest that in absence of LEE, Locus of Adhesion and Autoaggregation (LAA) may be involved as an alternative mechanism of adhesion to the human intestine, in which Hes, Iha, Ag43 and other virulence factors encoded in this locus could participate
Summary
Shiga Toxin-producing Escherichia coli (STEC) are a group of foodborne pathogens associated with gastrointestinal diseases, including acute diarrhea and dysentery. To determine the distribution of hes in our culture collection (167 STEC strains, including 48 LEE-negative STEC, and 12 fecal E. coli isolated from healthy subjects), PCR analysis was performed using primers hes_det1 + hes_det[2] (Supplementary Table 1), which are specific for this gene and do not amplify other allelic variants of the Hra family (Supplementary Note 1).
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