Variability in the Occupancy of Escherichia coli O157 Integration Sites by Shiga Toxin-Encoding Prophages.

Scott T Henderson,David Knupp,David W Lacher,Galeb S Abu-Ali,Shannon D Manning,James T Rudrik,Pallavi Singh

doi:10.3390/toxins13070433

Abstract

Escherichia coli O157:H7 strains often produce Shiga toxins encoded by genes on lambdoid bacteriophages that insert into multiple loci as prophages. O157 strains were classified into distinct clades that vary in virulence. Herein, we used PCR assays to examine Shiga toxin (Stx) prophage occupancy in yehV, argW, wrbA, and sbcB among 346 O157 strains representing nine clades. Overall, yehV was occupied in most strains (n = 334, 96.5%), followed by wrbA (n = 213, 61.6%), argW (n = 103, 29.8%), and sbcB (n = 93, 26.9%). Twelve occupancy profiles were identified that varied in frequency and differed across clades. Strains belonging to clade 8 were more likely to have occupied sbcB and argW sites compared to other clades (p < 0.0001), while clade 2 strains were more likely to have occupied wrbA sites (p < 0.0001). Clade 8 strains also had more than the expected number of occupied sites based on the presence of stx variants (p < 0.0001). Deletion of a 20 kb non-Stx prophage occupying yehV in a clade 8 strain resulted in an ~18-fold decrease in stx2 expression. These data highlight the complexity of Stx prophage integration and demonstrate that clade 8 strains, which were previously linked to hemolytic uremic syndrome, have unique Stx prophage occupancy profiles that can impact stx2 expression.

Highlights

Shiga toxin-producing Escherichia coli (STEC), which includes strains belonging to serogroup O157 and other non-O157 serogroups, is a major foodborne pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome (HUS) in some cases [1]
E. coli O157:H7 strains are highly diverse and have previously been considered ‘phage factories’ [32] when referring to the extensive diversity of prophages that contribute to the evolution of this important foodborne pathogen
The genes encoding the three Shiga toxin (Stx) variants, namely, stx1a, stx2a, and stx2c, are found on distinct lambdoid prophages that preferentially insert into the O157:H7 chromosome at four key loci: yehV, argW, wrbA, and sbcB [14,15,16]

Summary

Introduction

Shiga toxin-producing Escherichia coli (STEC), which includes strains belonging to serogroup O157 and other non-O157 serogroups, is a major foodborne pathogen that causes hemorrhagic colitis and hemolytic uremic syndrome (HUS) in some cases [1]. Production of Stx and/or Stx is most common, though multiple variants have been described [6]. These Stx variants can be found in different combinations that differ in their ability to cause severe disease. Stx2-producing strains, for example, have been correlated with more severe disease outcomes in several epidemiological studies in different locations [7,8,9,10,11]. The Stx2a lysogenic phage was shown to control a type III secretion system, which is a critical virulence trait found in some STEC

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Conclusion