title: Immunomagnetic separation as a sensitive method for isolating Escherichia coli O157 from food samples.
abstract: Minced beef samples inoculated with Escherichia coli O157 were cultured in buffered peptone water supplemented with vancomycin, cefsulodin and cefixime (BPW-VCC) and subcultured to cefixime tellurite sorbitol MacConkey (CT-SMAC) agar both directly and after immunomagnetic separation (IMS) of the organism with magnetic beads coated with an antibody against E. coli O157 (Dynabeads anti-E. coli O157, Dynal, Oslo). E. coli O157 was recovered from initial inocula of 200 organisms/g by direct subculture and 2 organisms/g by IMS. Twelve strains of E. coli O157 of different combinations of phage type, H antigen and toxin genotype were all recovered from initial inocula of two organisms/g by IMS. Non-specific binding of other organisms to the magnetic beads could be reduced by washing of the beads in PBS with Tween-20 0.002-0.005% E. coli O157 was not bound by magnetic coated with an unrelated antibody. During investigation of a dairy herd that was possibly linked to a small outbreak of infection with E. coli O157, the organism was isolated from 2 of 279 forestream milk samples from individual cattle; both isolates were made only by the IMS technique. IMS is rapid, technically simple, and a specific method for isolation of E. coli O157 and will be useful in epidemiological studies.
authors.affiliation: Public Health Laboratory, Sheffield.
authors.forename: D J
authors.initials: DJ
authors.lastname: Wright
authors.forename: P A
authors.initials: PA
authors.lastname: Chapman
authors.forename: C A
authors.initials: CA
authors.lastname: Siddons
mesh_terms: D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000254:growth & development / Q000302:isolation & purification*; D005069:Evaluation Studies as Topic; D005516:Food Microbiology; D018189:Immunomagnetic Separation; D008460:Meat / Q000382:microbiology*; D008863:Microspheres; D008892:Milk / Q000382:microbiology*; D012680:Sensitivity and Specificity