Streptococcus mutans from caries-active and caries-free individuals

A collection of strains of Streptococcus mutans from caries-active (CA strains) and caries-free individuals (CF strains) has been isolated and investigated for possible differences in pathogenicity. A series of 16 isolates of Strept mutans has been shown previously to differ in adherence to apatite and in release of calcium from apatite on culture (NOF 1997). Objectives: Further studies on this strain collection were performed in order to examine these apparent strain differences in detail. Methods: Bacteriocin-like activity was investigated by stab-inoculation of each of the test strains into pour-plates containing, separately, each of the test strains and 25 laboratory isolates of oral streptococci and other organisms. Electronmicroscopic investigation of CA and CF strains was carried out using negative staining to observe the presence of “fuzzy coat”. Immunoelectron microscopy using anti-crude fimbrial antibody and gold labelling was performed to determine possible differences in fimbriation of the CA and CF strains Results: Although CA strains showed more bacteriocin-like inhibition against other mutans streptococci (3.4 vs 1.2 strains; P<0.01), the CF strains were more inhibitory to other oral commensals (88/126 vs 59/126 tests; P<0.001). Despite considerable strain variation, a clear trend was noted of a thicker “fuzzy coat” layer for the CF strains (P=0.057) compared with CA strains. Almost all strains showed gold binding in this outer layer and no clear differences between CA and CF strains were observed. Conclusions: Clear morphological and behavioural differences appear to exist between strains of Strept. mutans although the mechanisms by which these differences affect the cariogenic potential of the strain are not yet clear.