Cariogenic virulence characteristics of mutans streptococci isolated from caries-active and caries-free adults

The objective of the study was to compare aciduricity (ability, to live in acid), acidogenicity (ability to produce acid), and intracellular polysaccharide production of mutans streptococci (MS) strains isolated from caries-active (CA, with one or more cavitated lesions) and caries-free (CF, with no clinically observable new caries in the last five years) adults. Forty-three MS strains from 17 of 17 CA adults, and 14 strains from eight of 12 CF adults were investigated. MS isolates' growth, survival, and pH reduction in pH 3.5-7.0 broths were evaluated to compare their acidogenicity and aciduricity. Extracellular water-soluble polysaccharide (WSP) and water-insoluble polysaccharide (WISP) was extracted from MS culture in BHI broth with 5 percent sucrose and assessed by a colorimetric anthrone-sulfuric acid microassay. No significant differences in mean aciduricity were found between CA and CF MS isolates (P>0.05, t test). However, significantly more CA subjects (29 percent) were colonized by MS strains with aciduricity above the average than CF subjects (13 percent, Fisher's exact test, P<0.05). Furthermore, CA MS strains produced significantly more acid at pH<5 (Mann-Whitney, P<0.05) and significantly more CA subjects were colonized with more acidogenic MS at pH<4.5 (Fisher's exact test, P<0.01). Similarly, CA MS isolates produced significantly more WISP than CF (Mann-Whitney test, P<0.01) while no statistical difference was found in WSP between the two groups. More CA subjects were colonized by multiple strains with aciduricity, acidogenicity, and polysaccharide synthesis ability above average. The study indicated that differences in acidogenicity, aciduricity, and polysaccharide synthesis in strains of MS may partially contribute to increased caries activity.