ANTIGENIC VARIATION IN POPULATIONS OF STREPTOCOCCUS SALIVARIUS ISOLATED FROM THE HUMAN MOUTH

Populations of Streptococcus salivarius CM6 exhibited antigenic variation while colonizing the mouth and intestinal canal of gnotobiotic rats. Variants which no longer produced detectable levels of one or more of 5 antigenic components discernible by immunoelectrophoresis were isolated in low proportions as early as 3 days after mono-infection of germ-free rats; almost all isolates obtained 2 weeks after infection were variants. Oral and faecal isolates attached less well than the parent strain to human or rat buccal epithelial cells. Variants altered with respect to 2 of the 5 components emerged first and such variants were the most common. These 2 components could not be detected in Strep. salivarius cells following treatment with trypsin. There were no variants of laboratory stock cultures of strain CM6 over a 3-yr period. The relative predictability of the emergence of variants in gnotobiotic rats suggests that a specific selection pressure was responsible, part of which was due to an immune response of the animals suggested by the emergence of variants more quickly in animals previously immunized with formalin-killed CM6 cells. Emergence of variants was less in animals pretreated with cyclophosphamide, an immunosuppressant, or fed diets supplemented with large numbers of killed Strep. salivarius. Populations of Strep. salivarius colonizing papillae on the tongue dorsum, and of Streptococcus mutans colonizing approximal molar tooth surfaces in man, were antigenically heterogenous; in some instances, the proportions of antigenic subtypes appeared to fluctuate with time. © 1979.