Is Shiga Toxin-Producing Escherichia coli O45 No Longer a Food Safety Threat? The Danger is Still Out There.

Yujie Zhang,Vivian C.H Wu,Xiaohong Sun,Yen-Te Liao

doi:10.3390/microorganisms8050782

Abstract

Many Shiga toxin-producing Escherichia coli (STEC) strains, including the serogroups of O157 and most of the top six non-O157 serotypes, are frequently associated with foodborne outbreaks. Therefore, they have been extensively studied using next-generation sequencing technology. However, related information regarding STEC O45 strains is scarce. In this study, three environmental E. coli O45:H16 strains (RM11911, RM13745, and RM13752) and one clinical E. coli O45:H2 strain (SJ7) were sequenced and used to characterize virulence factors using two reference E. coli O45:H2 strains of clinical origin. Subsequently, whole-genome-based phylogenetic analysis was conducted for the six STEC O45 strains and nine other reference STEC genomes, in order to evaluate their evolutionary relationship. The results show that one locus of enterocyte effacement pathogenicity island was found in all three STEC O45:H2 strains, but not in the STEC O45:H16 strains. Additionally, E. coli O45:H2 strains were evolutionarily close to E. coli O103:H2 strains, sharing high homology in terms of virulence factors, such as Stx prophages, but were distinct from E. coli O45:H16 strains. The findings show that E. coli O45:H2 may be as virulent as E. coli O103:H2, which is frequently associated with severe illness and can provide genomic evidence to facilitate STEC surveillance.

Highlights

Shiga toxin-producing Escherichia coli (STEC), as one of the major foodborne pathogens, can produce Shiga toxins and cause severe human disease, such as diarrhea, hemorrhagic colitis, and hemolytic–uremic syndrome (HUS) [1,2,3]
Each of the three O45:H16 strains contained two different iss alleles, which were located on the Stx1a prophage and a suspected 50,703-bp prophage sequence, respectively. These findings show that the three environmental E. coli O45:H16 strains in this study were genomically conserved, with the virulence factors being carried by certain prophages
The results of this study show that the prophages carrying non-locus of enterocyte effacement (LEE) encoded type III translocated effectors were only identified in LEE-positive strains, including E. coli O45:H2 and E. coli O103:H2 strains, but were absent in the E. coli O45:H16 LEE-negative strains. This phenomenon will need to be investigated in future studies. This is the first study to report the genomic characterization of STEC O45 strains of different origins

Summary

Introduction

Shiga toxin-producing Escherichia coli (STEC), as one of the major foodborne pathogens, can produce Shiga toxins and cause severe human disease, such as diarrhea, hemorrhagic colitis, and hemolytic–uremic syndrome (HUS) [1,2,3]. E. coli O157 and the “top six” non-O157 serogroups, including O26, O45, O103, O111, O121, and O145, are the primary STEC pathotypes frequently associated with foodborne outbreaks around the world [5,6]. Among the non-O157 STEC serotypes, STEC O45 has been identified as a cause of sporadic cases of bloody diarrhea [1]. In 2005, the first STEC O45 outbreak occurred in New York City, in which a total of 52 inmates were sick with diarrhea or bloody diarrhea, likely resulting from exposure to an ill food worker [7,8]. Two E. coli O45:H2-associated outbreaks were reported to have caused 18 illnesses in the United States, and contaminated smoked game meat and goats were implicated as sources of contamination in these outbreaks [9]

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