Dj. Wright et al., IMMUNOMAGNETIC SEPARATION AS A SENSITIVE METHOD FOR ISOLATING ESCHERICHIA-COLI O157 FROM FOOD SAMPLES, Epidemiology and infection, 113(1), 1994, pp. 31-39
Minced beef samples inoculated with Escherichia coli O157 were culture
d in buffered peptone water supplemented with vancomycin, cefsulodin a
nd cefixime (BPW-VCC) and subcultured to cefixime tellurite sorbitol M
acConkey (CT-SMAC) agar both directly and after immunomagnetic separat
ion (IMS) of the organism with magnetic beads coated with an antibody
against E. coli O157 (Dynabeads anti-E. coli O157, Dynal, Oslo). E. co
li O157 was recovered from initial inocula of 200 organisms/g by direc
t 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 red
uced by washing of the beads in PBS with Tween-20 0.002-0.005 % E. col
i O157 was not bound by magnetic coated with an unrelated antibody. Du
ring investigation of a dairy herd that was possibly linked to a small
outbreak of infection with E. coli O157, the organism was isolated fr
om 2 of 279 forestream milk samples from individual cattle; both isola
tes were made only by the IMS technique. IMS is rapid, technically sim
ple, and a specific method for isolation of E. coli O157 and will be u
seful in epidemiological studies.