Detection of B. anthracis strain Sterne 7702 (+, 104 spores; −, no spore) in the presence of spores (concentration range, 105 to 108 spores per ml) from B. cereus, B. thuringiensis, and B. subtilis strains. Data represent the results of a Meso Scale Discovery immunoassay performed with A1 MAb as the capture antibody and R93 MAb as the AChE tracer.