A COMPARISON OF IMMUNOMAGNETIC SEPARATION AND DIRECT CULTURE FOR THE ISOLATION OF VEROCYTOTOXIN-PRODUCING ESCHERICHIA-COLI O157 FROM BOVINEFECES

Enhrichment culture (EC) in modified buffered peptone water followed b y immunomagnetic separation (IMS) with magnetic beads coated with an a ntibody against Escherichia coli O157 (Dynabeads anti-E. coli O157; Dy nal, Oslo) was compared with direct culture on cefixime rhamnose sorbi tol MacConkey agar (CR-SMAC) and cefixime tellurite sorbitol MacConkey agar (CT-SMAC) for the isolation of E. coli O157 from bovine faeces. When used to examine bovine faecal suspensions inoculated with 12 diff erent strains of E. coli O157, EC-IMS was c. 100-fold more sensitive f or detection of the organism than direct culture on either medium. Dur ing monitoring of a dairy herd, E. coli O157 was isolated from 84(8 . 2 %) of 1024 rectal swabs taken from cattle over a 4-month period; 23 (27 . 4 % of the 84 strains were isolated by both direct culture and I MS (15 of the 23 were isolated on both media, five on CT-SMAC only and three on CR-SMAC only), whereas 61 (72 . 6 %) strains were isolated b y IMS only. IMS is a sensitive and simple technique for the isolation of E. coli O157 from bovine faecal samples and should prove useful in elucidating further the epidemiology of this organism.