CALCIFICATION OF A CARIOGENIC STREPTOCOCCUS AND OF CORYNEBACTERIUM (BACTERIONEMA) MATRUCHOTII

The main aim of this investigation was to challenge the idea that cari ogenic streptococci do not calcify. Calcium uptake or calcification of Streptococcus mutans C180-2, proven to be an acidogenic and cariogeni c strain, was compared with calcium uptake and calcification of Coryne bacterium (Bacterionema) matruchotii, known as a ready calcifier. Bact eria were grown on Brain Heart Infusion Agar (BHIA) and on well-buffer ed semi-synthetic E-agar, both containing 1.4 mmol/L calcium, 2 g/L gl ucose, initial pH 7.4. Calcium uptake from BHIA by C. matruchotii (25 mmol Ca/kg wet bacterial cell mass), but not by S. mutans, was found. Grown as a plaque-like lawn on E-agar, the S. mutans cell mass concent rated calcium to 63 +/- 11 mmol/kg compared with 145 +/- 61 mmol/kg in C. matruchotii. X-ray diffraction confirmed the presence of crystalli ne apatite in the bacterial cell masses. Electron microscopy revealed crystals and mineralized deposits in both organisms. Heavy calcificati ons in some cells of S. mutans were seen. Calcification was partly inh ibited by magnesium ion and by methanehydroxybisphosphonate. S. sobrin us 6715, as well as freshly isolated S. mutans and S. sobrinus from pa tients, concentrated very large quantities of calcium, up to 500-fold from the medium, when maintained for several weeks on E-agar of initia l pH 7.6. Our observations widen the view on acidogenic bacteria as mi neralization agents and support the notion that members of the mutans group of streptococci may be involved in events that trigger heavy int racellular calcifications and, possibly, dental calculus formation.