A reagent is provided for the detection of an exotoxin protein produced by a beta-hemolytic streptococcus bacteria suspected of being present in a host biological fluid collected from a subject. An enzyme inhibitor is present to inhibit rogue protein modification of the substrate to prevent a false positive result of the color change. A kit is provided that is readily usable by an untrained user and merely requires that an element of the kit be contacted with a biological sample and thereafter no further actions are required by the user before a discernable color change is observed with visible or UV light and a positive/negative results reference card.