Distribution of espM and espT among enteropathogenic and enterohaemorrhagic Escherichia coli

Ana Arbeloa,Richard Bulgin,Cecilia López,María Pilar Alonso,Ghizlane Dahbi,Fabiana C Moreira,Jorge Blanco,Jesús E Blanco,Tânia A T Gomes,Miguel Blanco,Azucena Mora,Rosalia Ceferina Mamani,Gad Frankel

doi:10.1099/jmm.0.010231-0

Abstract

Enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) translocate dozens of type III secretion system effectors, including the WxxxE effectors Map, EspM and EspT that activate Rho GTPases. While map, which is carried on the LEE pathogenicity island, is absolutely conserved among EPEC and EHEC strains, the prevalence of espM and espT is not known. Here we report the results of a large screen aimed at determining the prevalence of espM and espT among clinical EPEC and EHEC isolates. The results suggest that espM, detected in 51 % of the tested strains, is more commonly found in EPEC and EHEC serogroups that are linked to severe human infections. In contrast, espT was absent from all the EHEC isolates and was found in only 1.8 % of the tested EPEC strains. Further characterization of the virulence gene repertoire of the espT-positive strains led to the identification of a new ζ2 intimin variant. All the espT-positive strains but two contained the tccP gene. espT was first found in Citrobacter rodentium and later in silico in EPEC E110019, which is of particular interest as this strain was responsible for a particularly severe diarrhoeal outbreak in Finland in 1987 that affected 650 individuals in a school complex and an additional 137 associated household members. Comparing the protein sequences of EspT to that of E110019 showed a high level of conservation, with only three strains encoding EspT that differed in 6 amino acids. At present, it is not clear why espT is so rare, and what impact EspM and EspT have on EPEC and EHEC infection.

Highlights

Enterohaemorrhagic Escherichia coli (EHEC) comprise a subgroup of Shiga-toxin producing E. coli that can cause bloody diarrhoea, haemorrhagic colitis and haemolyticuraemic syndrome
Screening O157 and non-O157 EHEC strains for the presence of espM and espT We determined the prevalence of espM and espT among 45 non-sorbitol fermenting EHEC O157 : H7
Our results show that espM is found in approximately 96 % of the strains belonging to the major EHEC serogroups: O26, O103, O111, O118, O145 and O157, and in a

Summary

Introduction

Enterohaemorrhagic Escherichia coli (EHEC) comprise a subgroup of Shiga-toxin producing E. coli that can cause bloody diarrhoea, haemorrhagic colitis and haemolyticuraemic syndrome (reviewed by Tarr, 1995). Enteropathogenic E. coli (EPEC) is the leading cause of mortality due to infantile diarrhoea in the developing world (reviewed by Chen & Frankel, 2005). G 2009 SGM Printed in Great Britain lesions, which are characterized by the close association of the bacteria with the enterocyte plasma membrane and localized breakdown of the brush border microvilli (Knutton et al, 1987; reviewed by Frankel & Phillips, 2008). The ability to induce A/E lesions is associated with the LEE pathogenicity island, which encodes gene regulators, intimin (Jerse et al, 1990), a type III secretion system (Jarvis et al, 1995), chaperones, translocator and effector proteins (reviewed by Garmendia et al, 2005a).

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