Population dynamics of Streptococcus mitis in its natural habitat

The purpose of this study was to examine the genetic structure of the typic al commensal Streptococcus mitis biovar 1 in its natural habitat in the hum an oral cavity and pharynx and to investigate the role that selected microb ial properties and host, spatial, and temporal factors play in determining the structure of the bacterial population. Consecutive samples were collect ed from buccal and pharyngeal mucosal surfaces of two infants, their four p arents, and two elderly individuals over a period of approximately 1 year. A total of 751 isolates identified as S. mitis biovar I were typed by restr iction endonuclease analysis (REA) and representative clones were typed by multilocus enzyme electrophoresis (MLEE). The genetic diversity of the S. m itis biovar I isolates collected from single infant hosts over a period of 9 to 10 months was found to be between 0.69 and 0.76, which is considerably higher than that previously observed for intestinal populations of Escheri chia coli. The study provides evidence of the existence of both transient a nd persistent clones in adult individuals. In the two infants, however, non e of 42 demonstrated clones were detected on more than a single occasion. S tatistical calculations showed that the ability to persist was not distribu ted at random in the S. mitis biovar I population. However, neither immunog lobulin Al protease activity nor the ability to bind alpha -amylase from sa liva was a preferential characteristic of persistent genotypes. In contrast to current concepts of climax ecosystems, the species niche in the habitat appears to be maintained predominantly by a succession of clones rather th an by stable strains. Several lines of evidence suggest that the major orig in of "new" clones is the many other habitats in the respiratory tract that are occupied by this species.