A method is provided for differentiation of the microorganisms associated with periodontal disease, such as Actinobacillus actinomycetemcomitans, Bacteroides gingivalis and Bacteroides intermedius, in a biological specimen. Thus, extracted antigens from any and all of the microorganisms are contacted with a microporous membrane having at least three discrete zones for immunological complexation. Antigens from each microorganism are complexed in specific zones so the operator can determine which microorganisms are present in the specimen by observing which zones have immunological complexes therein. Complexation occurs between the antigens and corresponding water-insoluble reagents which are composed of water-insoluble particles to which the appropriate antibodies are affixed. Detection of the complexes is achieved using labeled antibodies directed to the individual antigens. An article and kit useful in this method are also described.
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