Figure 2: ELISA detection of Escherichia coli O157:H7 cells. In a sandwich immunoassay, live (closed circles) and heat-killed E. coli O157:H7 (open squares) bacteria were reacted with anti-heat-killed E. coli O157:H7 capture antibody (15 μg/ml) bound to polystyrene microplate wells followed by reaction with AP-conjugated anti-heat-killed E. coli O157:H7 antibody and colorimetric substrate. Formation of colored product was measured and represented above as absorbance (at 405 nm) versus bacteria concentration.(Initial rates were determined using LINEST in Microsoft Excel as applied to the first four data points).