Comparison of selective broth and plating methods for isolation of Streptococcus mutans from root surface dental plaques.

Approximately 150 sound root surfaces in 44 subjects prone to root surface caries were sampled longitudinally to determine the microbial flora associated with root caries initiation. During the first 16 months of the study, a comparison of Streptococcus mutans recovery was made by using three bacteriological media: mitis-salivarius agar (MSA), mitis-salivarius-bacitracin-sucrose agar (MSB), and a partially selective mannitol-containing broth. Total streptococcal and S. mutans populations were found to be much lower than in previous reports. MSB was more selective; S. mutans was detected in many samples when its numbers were too low for isolation on MSA. However, recovery of S. mutans was greater on MSA than on MSB for most samples yielding colonies on both media. Mannitol-containing broth used as an enrichment medium yielded the highest frequency of S. mutans isolation among the three media.