Physiological and serological variation in Streptococcus mitis biovar 1 from the human oral cavity during the first year of life

ObjectiveThe purpose of the study was to explore the physiological and antigenic diversity of a large number of Streptococcus mitis biovar 1 isolates in order to begin to determine whether these properties contribute to species persistence.DesignS. mitis biovar 1 was collected from four infants from birth to the first year of age. At each of eight to nine visits, 60 isolates each were obtained from the cheeks, tongue and incisors (once erupted) yielding 4440 in total. These were tested for production of neuraminidase, β1-N-acetylglucosaminidase, β1-N-acetylgalactosaminidase, IgA1 protease and amylase-binding. Antigenic diversity was examined by ELISA and Western immunoblotting using antisera raised against S. mitis biovar 1 NCTC 12261T and SK145.ResultsThree thousand three hundred and thirty (75%) of the isolates were identified as S. mitis biovar 1 and 3144 (94.4%) could be divided into four large phenotypic groups based on glycosidase production. Fifty-four percent of the isolates produced IgA1 protease, but production was disproportionate among the phenotypes. Between one-third and one-half of the strains of each phenotype bound salivary α-amylase. Antisera against strains NCTC 12261T and SK145 displayed different patterns of reactivity with randomly selected representatives of the four phenotypes.ConclusionsS. mitis biovar 1 is physiologically and antigenically diverse, properties which could aid strains in avoiding host immunity and promote re-colonization of a habitat or transfer to a new habitat.