Enumeration of mutans streptococci in clinical samples by using monoclonal antibodies

Mutans streptococci have been strongly associated with dental caries. Two members of this group of bacteria, Streptococcus mutans and Streptococcus sobrinus, are often found in human dental plaque. Identification of mutans streptococci on the basis of sugar fermentation is troublesome and easily leads to erroneous conclusions. Furthermore, the recovery on selective media differs for different species. This causes incorrect enumeration of S. mutans and S. sobrinus in clinical samples. The aim of this study was to develop a method for simultaneous identification and enumeration of S. mutans and S. sobrinus in dental plaque and saliva samples. With this immunoblot technique (IBT), significantly more plaque samples containing S. sobrinus were detected than on the selective medium Trypticase-yeast-cysteine-sucrose-bacitracin agar (TYCSB) (P less than 0.01). The numbers of plaque samples harboring S. mutans were equal on TYCSB and by IBT. However, the numbers of CFU of S.mutans as well as of S. sobrinus detected with the IBT were significantly higher than those obtained on TYCSB (P less than 0.001). The recovery of primary isolations of S. sobrinus on TYCSB seems to have been inhibited in 26 of the 45 S. sobrinus-containing plaque samples. False-positive or false-negative reactions with the IBT were not found.