A modified mitis salivarius medium for a caries diagnostic test.

A new medium, MSKB, composed of mitis salivarius agar base, sorbitol, kanamycin sulfate and bacitracin, has been developed that is more selective for recovery of mutans streptococci (mutans) than the so called mitis salivarius bacitracin (MSB) medium. MSB and MSKB were compared for recovery and selectivity of mutans by plating saliva samples as well as pure cultures on both media. Sixty saliva samples were plated and counted for mutans and non-mutans colonies. Thirty-six samples had greater numbers of non-mutans on MSB than on MSKB, and 14 of the 36 had non-mutans colonies that could be visually confused with mutants. The recovery of mutans on MSKB was approximately 13% less than on MSB. The selectivity and recovery of MSB and MSKB were evaluated over 1-5 months of storage at 4 degrees C. Streptococcus anginosus grew on MSB after 1 month, but not on MSKB. Streptococcus milleri type 2 grew on both media after 4 months.