Serological studies of ungroupable Neisseria meningitidis.

Verification that Slaterus' Neisseria meningitidis serotypes X, Y, and Z are groups distinct from each other and from groups A, B, C, and D was made by use of the tube agglutination test on absorbed and unabsorbed antisera. A significant number of meningococcal strains in this country, which could not be classified serologically with standard antisera prepared to Branham's neotype A, B, C, and D strains, were grouped specifically with antisera prepared to the Slaterus types. The strains grouped as X, Y, and Z were from various geographical areas of the United States and were isolated from both carriers and cases. Over a 2-year period, the cultures tested ranged in predominance in descending order as follows: group B, C, Y, X, Z, A, and D. It is recommended that Slaterus' types should be considered as standard groups and follow in alphabetical order with the standard A, B, C, and D groups; i.e., X would be designated as group E, Y as group F, and Z as group G. It was observed that false-grouping cross-reactions could be greatly reduced by reconstituting the lyophilized grouping antisera in 50% glycerol-water. Of 99 cultures which could not be specifically grouped with antisera reconstituted in distilled water, 19 were specifically grouped with antisera reconstituted in 50% glycerol-water.