New serotypes were sought among 165 clinical isolates of group-B streptococci that were untypable by antisera for the conventional types Ia, Ib, II and III. The strains were tested for sialic acid, an integral component of the group-B streptococcal type-polysaccharides; trypsin-treated bacteria were tested by slideagglutination with the sialic-acid-specific lectin from the snail Sialic acid was detected in 96 of the strains; in 95 of these, new type antigens were identified serologically (type IV, 52; provisional type V, 34; candidate type NT6, seven; provisional type V and candidate type NT6, one; candidate type 7271, one); the remaining strain was found to possess a small amount of Ia antigen. Sialic acid was not detected in 69 strains, and none of these possessed a polysaccharide type-antigen. Chemical measurement of the sialic-acid content of cultures by Aminoff's method gave results in conformity with the lectin-agglutination test and the presence of polysaccharide type-antigens.


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