Phenotypic and genotypic diversity of Streptococcus sanguis in infants

Streptococcus sanguis comprises a heterogeneous group of oral streptococci indigenous to the oral cavity of humans. A total of 289 isolates from an in fant population (n=37) were tentatively identified as S. sanguis on the bas is of the distinctive colony morphology as shown on MM10-sucrose non-select ive medium. These isolates were divided into four biovars of S. sanguis as determined by an extended panel of biochemical attributes. Chromosomal DNA was extracted from each isolate, and an AP-PCR fingerprint profile was obta ined to allow study of the diversity within and among the infants. In this study, all four biovars of S. sanguis were detected in the infants. A wide genotypic diversity of S. sanguis was observed among these isolates; on ave rage, each infant harbored 2.7 unique amplitypes as shown by the AP-PCR fin gerprints. To explore the phylogenic relationship among these S. sanguis is olates, 20 strains representing the four biovars were selected at random fo r sequencing of their 16S rDNA and 16S-23S rDNA intergenic spacer chromosom al loci. Two major sequence patterns were identified within the 16S rDNA se quences. A phylogenic analysis showed that members from each of the four bi ovars of S. sanguis bore close relationship with the type-strain ATCC 10556 sequence, and that all of the isolates representing the four biovars could be clustered into two main phylotypes. The biovars were distributed throug hout the phylotypes, indicating no correlation between the genetic and phen otypic groupings.