Increased sensitivity of the rapid hydrophobic grid membrane filter enzyme-labeled antibody procedure for Escherichia coli O157 detection in foods and bovine feces

Abstract

Several strains of Escherichia coli O157:H7 artificially inoculated into vegetables and dairy products were recovered on hydrophobic grid membrane filters and enumerated by an enzyme-labeled antibody assay. The mean of the recoveries from 12 fresh vegetables was 108.8%, whereas that from 10 dairy products was 93.2%. Modified tryptic soy broth at 43°C with shaking at 100 rpm provided optimum recovery of the organism from meat, with a sensitivity of ≤ 1 CFU/g, which is 10 times more sensitive than direct plating. The method performed equally well with vegetable and dairy products. Tryptic soy broth, however, under the same conditions gave the best results for fecal samples. Of 22 asymptomatic dairy cattle, reported as having positive Brucella titers when assayed with polyclonal antibodies, eight were found to contain E. coli O157 in their feces as demonstrazed by the enzyme-labeled antibody assay by using monoclonal antibodies. This finding may explain some of the false-positive Brucella tests.