Identification and characterisation of Escherichia coli strains of O157 and non-O157 serogroups containing three distinct Shiga toxin genes

Three Shiga toxin (Stx)-producing Escherichia coli (STEC) strains from pati ents with diarrhoea were identified, each of which contained three distinct sfx genes (stx(1), stx(2) and stx(2c),), The strains belonged to the serot ypes O52:H19, O75:H- and O157:H- and harboured eae and EHEC-hly sequences, Colony-blot immunoassay was used to demonstrate that both major types of St x were expressed, The association of str genes with either phage or phage D NA was demonstrated in all three strains. Isolated phage DNA from all strai ns contained stx(1) sequences, but sfx(2) sequences were found only in phag e DNA of two of these strains, The presence of three distinct stx genes may enhance the virulence of STEC strains and should be monitored. The observa tions demonstrate not only the potential of sfx genes to spread within diff erent serotypes, but also their capacity to accumulate within a single stra in.