Distribution of espM and espT among enteropathogenic and enterohaemorrhagic Escherichia coli

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Abstract
EnterohaemorrhagicEscherichia coli(EHEC) and enteropathogenicE. coli(EPEC) translocate dozens of type III secretion system effectors, including the WxxxE effectors Map, EspM and EspT that activate Rho GTPases. Whilemap, which is carried on the LEE pathogenicity island, is absolutely conserved among EPEC and EHEC strains, the prevalence ofespMandespTis not known. Here we report the results of a large screen aimed at determining the prevalence ofespMandespTamong clinical EPEC and EHEC isolates. The results suggest thatespM, 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,espTwas 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 theespT-positive strains led to the identification of a newζ2 intimin variant. All theespT-positive strains but two contained thetccPgene.espTwas first found inCitrobacter rodentiumand laterin silicoin 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 whyespTis so rare, and what impact EspM and EspT have on EPEC and EHEC infection.