Applications of DNA probes for Vero cytotoxin-producing Escherichia coli

Vero cytotoxin-producing Escherichia coli (VTEC) are now recognized as important aetiological agents in human disease. The symptoms of VTEC infection range from mild non-bloody diarrhoea to severe conditions such as haemorrhagic colitis (HC) and haemolytic uraemic syndrome (HUS). Two types of Vero cytotoxin (VT), VT1 and VT2, have been identified. The genes controlling production of VT1 and VT2 are phageencoded in several E. coli strains and DNA probes have been developed from cloned genes derived from these VT phages. Recently, synthetic oligonucleotide probes for VTEC have also been prepared and evaluated. The VT probes have been labelled radioactively and also non-radioactively with digoxigenin and biotin. Present applications of VT probes include detection of VTEC in faecal samples from patients with diarrhoea, HC or HUS and also the examination of different foods for the presence of VTEC. The proportion of VTEC in the faecal flora or foods may be low, often less than 1%. The use of DNA probes allows several hundred colonies from a sample to be examined and by this technique VT genes were detected in 30-40% of faecal specimens from patients with HC or HUS. Use of methods such as the polymerase chain reaction for amplification of the target genes combined with DNA probes should result in an increased sensitivity for the detection of VTEC.