Virulence factors of Escherichia coli O157 and other Shiga toxin-producing E-coli

Shiga toxin-producing Escherichia roll O157 are important enteropathogens causing outbreaks of haemorrhagic colitis and haemolytic uraemic syndrome. Strains of E. coli belonging to other serogroups also produce Shiga toxins but are less frequently isolated from cases of diarrhoeal illness despite humans having greater exposure to these organisms in food and the environment. It is generally considered that E. coli O157 is more virulent than these other Shiga toxin-producing E. coli. The question of which factors make toxigenic E. coli O157 more virulent is unanswered. In this review the various virulence properties of E. coli O157 and their incidence in non-O157 Shiga toxin-producing E. coli are described. The most important factors for E. coli O157 are the production of Shiga toxin 2 and the adhesin intimin. The role of some of the other virulence factors, such as enterohaemolysin, a serine protease (EspP) and a catalase/peroxidase (Katp), in infection may be low. Uncharacterized virulence properties such as a clostridial-like toxin and haemoglobin uptake require further study and it is likely that other virulence properties remain to be discovered.