Genetic and Functional Analyses of Virulence Potential of an Escherichia coli O157:H7 Strain Isolated From Super-Shedder Cattle.

Lin Teng,Kwangcheol Casey Jeong,Shinyoung Lee,Dongjin Park

doi:10.3389/fcimb.2020.00271

Abstract

Shiga toxin (Stx)-producing Escherichia coli (STEC) O157:H7 is an enteric pathogen that causes life-threatening disease in humans, with cattle being major natural reservoirs. A group of STEC O157:H7 with a dramatic combination of high virulence potentials and super-shedder bovine origin have been isolated. Here, an STEC O157:H7 isolate, JEONG-1266, was analyzed by comparative genomics, stx genotyping, and phenotypic analyses. The phylogenetic typing and whole-genome comparison consistently showed that JEONG-1266 is genetically close to EC4115 (one of 2006 Spinach outbreak isolates) and SS17 (an isolate from super-shedder cattle) strains, all of which belong to lineage I/II and Clade 8. Both lineage I/II and Clade 8 are known to be mostly associated with clinical strains with high virulence and severe clinical symptoms. Further, JEONG-1266, like EC4115 and SS17, harbors stx2a/stx2c genes, and carries Stx-encoding prophages, specifically the φstx2a-γ subtype. Possession of the φstx2a-γ subtype of Stx-encoding prophages and production of Stx2a have been shown to be a key signature associated with hypervirulent STEC O157:H7 strains. In silico virulence typing elucidated JEONG-1266, EC4115, and SS17 shared a highly conserved profile of key virulence genes at the nucleotide sequence level. Consistently, phenotypic data showed that JEONG-1266 expressed a high level of Stx2 toxins and had the full capacity of adhesion in vitro. Taken together, our study suggests that JEONG-1266 may represent an emerging STEC O157:H7 group, which are hypervirulent strains that originate from super-shedders, that can be a threat to food safety and public health.

Highlights

Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 has become a major public health burden worldwide (Arthur et al, 2013; Munns et al, 2015), especially in Japan, Scotland and North America (Mead et al, 1999; Sakuma et al, 2006; Pollock et al, 2007), since it was first identified as a foodborne pathogen in 1982
Compared to the three reference strains of STEC O157:H7 including a super-shedder strain (SS17) and two outbreak-associated strains (EDL933 and EC4115), the chromosome of JEONG-1266 was slightly shorter in size, containing fewer coding sequences (CDSs) (Table 1)
Phylogenetic analysis with 26 E. coli O157 strains from various sources showed that JEONG-1266 belongs to the prominent cluster including all spinach outbreak strains and super-shedder strains (Clade III, Figure 2A)

Summary

Introduction

Shiga toxin (Stx)-producing Escherichia coli (STEC) O157 has become a major public health burden worldwide (Arthur et al, 2013; Munns et al, 2015), especially in Japan, Scotland and North America (Mead et al, 1999; Sakuma et al, 2006; Pollock et al, 2007), since it was first identified as a foodborne pathogen in 1982. Jeon et al reported super-shedders disseminated E. coli O157 to other cattle housed in the same pen, causing the E. coli O157 shed by super-shedders predominant in the farm (Jeon et al, 2013) Ecological dynamics of these predominant E. coli O157 and super-shedders increase the frequencies of contamination in animal food products such as beef and milk (Gyles, 2007). It is of great importance to understand the characteristics of the E. coli O157 strains from the super-shedders to reduce the prevalence of this pathogen in food-producing animals and to curtail the number of foodborne outbreaks and human illnesses

Methods

Results

Conclusion