Non-O157 : H7 Shiga toxin (verocytotoxin)-producing Escherichia coli strains: epidemiological significance and microbiological diagnosis

Shiga toxin (Stx)-producing Escherichia coli (STEC) are important causes of diarrhoea and the haemolytic uremic syndrome (HUS). The most common STEC s erotype implicated worldwide is E. coli O157:H7 that is diagnosed using pro cedures based on its typical phenotypic feature, the lack of sorbitol ferme ntation. In addition to E. coli O157:H7, a variety of non-O157:H7 STEC stra ins that usually ferment sorbitol and are thus missed by using the diagnost ic protocol for E. coli O157:H7 have been isolated from patients. Among the se sorbitol-fermenting (SF) non-O157:H7 STEC, SF E. coli O157:H- and non-O1 57 STEC strains of serogroups O26, O103, O111 and O145 have emerged as sign ificant causes of HUS and diarrhoea in continental Europe and have been ass ociated with human disease in other parts of the world. Microbiological dia gnosis of non-O157:H7 STEC strains is difficult due to their serotype diver sity and the absence of a simple biochemical property that distinguishes su ch strains from the physiological intestinal microflora. Screening for non- O157:H7 STEC and their isolation from stools is presently based on the dete ction of Stx production or stx genes that are common characteristics of suc h strains. Molecular subtyping of the most frequent non-O157 STEC demonstra ted that strains of serogroups O26, O103 and O111 belong to their own clona l lineages and show unique virulence profiles. SF STEC O157:H- strains that have been isolated mostly in Central Europe represent a new clone within E . coli O157 serogroup which has its own typical combination of virulence fa ctors.