Isolation of Escherichia coli O157:H7 using O157 specific antibody coated magnetic beads

Escherichia coli O157 specific antibody, coated on magnetic beads, was used to concentrate and remove the E. coli O157:H7 from mixed cultures and meat samples. The problem of nontarget organism carryover was addressed by adding Protamine to the culture-bead sample, washing the beads three times in saline, and changing the test tubes with each wash. These modifications reduced the nontarget colony counts obtained from uninoculated meat samples. This procedure enabled consistent recovery of E. coli O157:H7 from inoculated meat samples. The percentage of E. coli O157:H7 cells captured, compared to the total number of cells captured, ranged from 48 to 100%. Two strains of E. coli O157, :H7 and :non-H7, appeared to compete with one another and thus reduce or prevent isolation.