THE ISOLATION AND DETECTION OF ESCHERICHIA-COLI O157 BY USE OF IMMUNOMAGNETIC SEPARATION AND IMMUNOASSAY PROCEDURES

The use of immunomagnetic separation (IMS) techniques has been reporte d to reduce the total test time, and improve the sensitivity, of micro biological tests done on foods. This approach is being adopted in epid emiological investigations into suspected foodborne outbreaks of Esche richia coli O157 infection and has gained acceptance by public health laboratories and the food industry. This study demonstrated the abilit y of a commercially available IMS procedure, Dynabeads anti-E. coli O1 57, to enable detection of a few cells of E. coli O157 in 25 g of inoc ulated minced beef, giving results 1 d earlier than a cultural analysi s of similar sensitivity. With correct choice of enrichment broths, IM S may increase isolation rate of E. coli O157 compared to that obtaine d using conventional cultural methods. It is suggested that this may b e due to an increase in relative concentration of E. coli O157 compare d with the background microflora present in minced beef, which may red uce reliability of non-IMS detection procedures by masking or mimickin g target cells on selective/differential solid media. The use of an im munoassay incorporating an IMS step, EHEC-Tek (Organon-Teknika), enabl ed detection of a few cells of E. coli O157 in 25 g of minced beef. Co mparison of the IMS-ELISA with a standard ELISA procedure (Tecra) indi cated the sensitivity of the latter system to be greater, perhaps resu lting in the higher isolation rate. The use of a method to reliability isolate and detect extremely low levels of E. coli O157 in a food is necessary to aid reduction in the incidence of this most serious of fo odborne pathogens.