A comparison of immunomagnetic separation, direct culture and polymerase chain reaction for the detection of verocytotoxin-producing Escherichia coli O157 in human faeces.

Verocytotoxin-producing Escherichia coli O157 (O157 VTEC) has become well recognized as an important enteric pathogen. The number of organisms present in environmental and clinical samples may be low and efforts have been made to increase the sensitivity of O157 VTEC detection. Immunomagnetic seperation (IMS) has been shown to improve O157 VTEC detection in bovine faeces and food samples. A milkborne outbreak of O157 VTEC infection allowed us to compare the isolation rates from human faeces by IMS, direct faecal culture on sorbitol-MacConkey agar and a PCR test for verotoxin gene carriage. Of 142 faecal samples examined, 20 were positive on both direct culture and IMS and a further 13 on IMS alone. Therefore, IMS increased the detection rate of individual cases of O157 VTEC infection and also compared well with PCR. We recommend IMS for use in routine diagnostic laboratories where a more sensitive method than direct faecal culture is required for O157 VTEC isolation.