PHENO-GENOTYPING OF VEROTOXIN-2 (VT2)-PRODUCING ESCHERICHIA-COLI CAUSING HEMORRHAGIC COLITIS AND HEMOLYTIC-UREMIC SYNDROME BY DIRECT ANALYSIS OF PATIENTS STOOLS

The subtype of verotoxin 2 (VT2) found in 22 VT2-positive stool sample s from severely diseased Italian and German children with haemorrhagic colitis or haemolytic uraemic syndrome, or both, and that produced by the corresponding VT-producing Escherichia coli (VTEC) strains isolat ed from the stools were studied by cytotoxicity sero-neutralisation as says and by polymerase chain reaction (PCR) amplification of the VT2 B -subunit gene, followed by restriction fragment length polymorphism (R FLP) analysis. The free faecal toxin was serotyped as the classical VT 2 in 21 stool samples, and as the VT2 variant VT2c in one. For all but one of the VTEC isolates, the toxin phenotype was consistent with the type of VT produced in vivo and found in the corresponding stool samp les. Genotyping was in agreement with phenotyping for those strains ha rbouring a single type of VT2 gene, Three O157:H7 isolates carrying bo th VT2 and VT2c genes had the VT2 phenotype, instead of the expected V T2c phenotype. Direct PCR analysis of stools detected VT genes in only 11 of 20 VT-positive stool samples suggesting that the Vero cell cyto toxicity assay is more sensitive in diagnosing VTEC infection. Immunol ogical and genetic subtyping of VT2 performed directly on stool sample s from patients with haemolytic uraemic syndrome could be a useful com plementary approach to understanding the role of the different types o f VT in this syndrome.