[Specific activity of colored variants of N. meningitidis colonies]

The character of fluorescence of the colonies formed by serogroup A meningococci (229 strains) in oblique light and their activity in the agglutination test with group specific S and RD antisera to the meningococcal dissociant of the same serogroup were studied. Orange and orange-green colonies were found to have pronounced group-specific activity, and faint gray colonies changed the character of their agglutination with the group-specific antiserum up to the loss of agglutinability; and simultaneously their capacity for agglutination with the antiserum to the dissociant was revealed. The study of the character of fluorescence and the group-specific activity of meningococcal colonies belonging to other serogroups provided similar results.