Clinical isolates of Streptococcus mutans serotype c with altered colony morphology due to fructan synthesis

Abstract

Streptococcus mutans MT6801, MT6861, and MT6879, which form large mucoid colonies on mitis salivarius agar, were isolated from a mother and her two daughters. These isolates were identified as serotype c by immunodiffusion with serotype-specific antisera. The large colonies formed on sucrosecontaining agar were found to contain water-soluble fructan. The cell-free fructosyltransferase (FTase) activity of the strains which formed large colonies was five to eight times higher than that of serotype c S. mutans which produced small, rough colonies typical of this serotype. Furthermore, greater quantities of fructan were synthesized from sucrose by growing cells of MT6801 when compared with MT8148, a typical serotype c S. mutans. Glucosyltransferase and FTase could be isolated by chromatofocusing from culture supernatants of MT6801 and MT8148. The FTase activity of both strains was eluted at pH 4.5, and glucosyltransferase was released by elution with an NaCl linear gradient. The eluted FTase activity of MT6801 was significantly higher than that of MT8148. Strains MT6861 and MT6879 were also found to possess a similar property in terms of FTase activity. These results suggest that formation of large mucoid colonies by these strains is a consequence of high FTase activity.

Analysis of a DNA polymorphic region in the gtfB and gtfC genes of Streptococcus mutans

“…All of the other DNA variations identified in these strains were silent without affecting the amino acid sequence. In addition, most of the nucleotide changes were shared by the clinical isolates and a laboratory strain, MT-8148, originally from the National Institute of Health in Japan (17). The sequencing results confirmed our previous Southern blot analysis and identified DNA alterations none other than point mutations in the 5' coding regions of the gtB and gtC genes.…”

Analysis of the virulence of Streptococcus mutans serotype c gtfA mutants in the rat model system

“…We transformed two strains that were obtained as clinical dental isolates, one contained an indigenous 5.8-kb plasmid (UA101), and one was a plasmidless strain (UA130). We also transformed strain MT8148, which is considered a typical serotype c strain (41). Emr transformants were selected at erythromycin concentrations that ranged from 1 to 25 ,u.g/ml.…”

HIV Infection Affects Streptococcus mutans Levels, but Not Genotypes

“…Our descriptive subset study revealed that the phenotypic variance of S. mutans was greater than its genotypic variance, e.g., 4 different colony morphologies were isolated for participant 1, but all presented with an identical fingerprint. Although morphological characteristics have proved to be a useful tool in S. mutans identification on mitis-salivarius agar with optimal concentrations of sucrose and bacitracin, Okahashi et al previously illustrated that the same serotype of S. mutans could have different phenotypes based on the variations in glucans and fructans synthesis (Okahashi et al, 1984). The findings of our study provide new evidence to support the notion that S. mutans morphologic characteristics on MSB agar do not necessarily correspond to genotypic variance and are therefore not a reliable means of delineating S. mutans genotypes.…”