Objective: To establish a quantity detection method of Streptococcus mutans (Sm) and bacteria and compare the relationship between the number of these bacteria and the prevalence of dental caries in different people.
Methods: With specific primers for a unique sequence in a 14 kb HaeIII restriction fragment consistently presenting during detecting Sm by chromosomal DNA fingerprints, the total number of Sm and bacteria of 99 saliva samples were detected by real-time polymerase chain reaction (PCR) and statistically analyzed.
Results: The primers were specific for Sm and the minimum detectable level by real-time PCR was 0.1 microg/L. The total number of bacteria in the dental caries and people without caries was 51.4 x 10(8) cell copies/L and 221.6 x 10(8) cell copies/L respectively, in which the ratio of Sm to bacteria was 0.0193 and 0.0059 respectively. The differences were significantly different between the people with dental caries and those without caries in the total number of bacteria and the ratio of Sm to bacteria.
Conclusions: The primers can be used to detect the Sm by real-time PCR. The ratio of Sm to bacteria was closely associated with the prevalence of dental caries.