Mitis salivarius-bacitracin 10% sacarose agar for oral streptococci and Streptococcus mutans counts

The MSB Agar (mitis salivarius-bacitracin) 20% sacarose medium is frequently used for the isolation and count of total streptococci and Streptococcus mutans. Although it is considered a selective culture medium for this micro-organism, S. mutans recovery in this medium is much lower than in this Mitis Salivarius Agar (MSA). Because the number of S. mutans in saliva is used for estimating caries risk and activity from a microbiological stand point, the aim of this work was to find a modification of the MSB 20% sacarose medium so that it would offer not only selectivity in the isolation but also maximum recovery. This would detect people at risk more efficiency and would evaluate the preventive odontological treatments more accurately. The results show that: 1) the greatest recovery of total streptococci and S. mutans is obtained in the MSB 10% sacarose medium, 2) S. mutans must be incubated in aerobiosis and the total streptococci in a candle jar (10% CO2). MSB 10% sacarose medium is proposed as a choice medium for the microbiological estimation of cariogenic risk and activity, to detect infection levels and evaluate preventive odontological treatments.