Antigenic Variation in Populations of Oral Streptococci

Abstract

It is well established that human sera and secretions contain antibodies which react with strains of indigenous bacteria (1–5). The apparent ability of indigenous organisms to persistently colonize humans and animals despite the presence of antibodies reactive with them suggests either: 1) that the host immune response to indigenous organisms is comparatively feeble and does not significantly influence their colonization, or 2) populations of indigenous species are able to evade the host’s immune response by undergoing antigenic variation. This phenomenon is well known to occur in certain viral (6) and protozoan diseases (7), but it has been studied less well in bacterial infections. Populations of Vibrio cholerae have been observed to change serotype while colonizing gnotobiotic mice (8), and antigenic changes have been noted in isolates of Camplylobacter fetus during natural infections in cattle (9); antigenic alterations may also occur in hemolytic streptococci following serial mouse passage (10).