Abstract: A method for performing an assay to differentiate between related taxa of micoorganisms, comprising the steps of providing a support having a plurality of zones, each zone comprising immobilized antibody to an enzyme found in a particular microorganism, wherein the antibody in the zone is specific to the enzyme, but not to corresponding enzyme of other taxa to be determined in the assay; contacting the zones with a sample suspected of containing one of the particular microorganisms; permitting enzyme in the sample to become bound by antibody in one or more of the zones; and determining which of the taxa were present in the sample by determining to which of the zones the enzyme has become bound. The determining step may comprise adding a substrate for the enzyme to the support after the enzyme has become bound thereto, wherein the substrate, after being acted on by the enzyme, creates a detectable signal.