Optimal antibody concentration. The preliminary study to
determine the optimal concentration of the HRP-labeled goat
anti-E. coli O157:H7 antibody concentration was designed to
reveal the intended effects of extreme antibody concentrations
(false-positive and false-negative reactions) in the CLI protocol.
The substrate reactions were very weak and gradually
faded beyond recognition with antibody dilutions greater than
or equal to 0.03125 mg ml21 (data not shown). The antibody
concentration that worked best in the preliminary investigation
of a single incubation time was 0.0625 mg ml21
, based on
substrate color retention for the true positives and the absence
of substrate color for the true negatives.