The antibody concentration and the conjugate incubation time were further optimized by using two false-positive strains,
O157:H45 (KPL 300386) and O157:H3 (KPL 300489), which were chosen because of their initial weak reaction with the
O157-agglutinating antisera (Difco) during preliminary testing. These strains, along with the two O157:H7 strains (MDLand5), provided excellent measures of specificity for the further refinement of an effective antibody concentration and conjugate
incubation time for use in the CLI.