Identification and grouping of Neisseria meningitidis directly on agar plates by coagglutination with specific antibody-coated protein A-containing staphylococci.

It has been shown that Neisseria meningitidis can be grouped by coagglutination directly upon growth on sheep blood or chocolate agar plates. All positive reactions were group specific, and only a single colony was required for a positive reaction. There was variation seen in the effectiveness of commercial antisera in preparing sensitive reagents. Certain throat and sputum isolates of group Z organisms failed to react by coagglutination, although they would react directly with antiserum in whole-cell agglutination. This problem remains unresolved but may not be greatly significant in laboratory use of this method since group Z is rarely associated with disease.