Quantitative determination of Streptococcus mutans by using competitive polymerase chain reaction

Mutans streptococci are among the range of pathogens strongly related to human dental caries. The determination of total amounts of these pathogens as well as their proportion in relation to other oral bacteria is of interest for the assessment of the risk that a patient runs of developing dental caries. This paper presents a competitive polymerase chain reaction (PCR) method for the specific quantitative determination of Streptococcus mutans which uses a homologous DNA for internal standardisation. For quantification of these bacteria, calibration curves were obtained by coamplification of known amounts of S. mutans DNA in the presence of different known amounts of the competitor DNA. The same procedure was performed with known amounts of cultured S. mutans cells. In a clinical study, the reliability of the newly developed quantitative PCR method was assessed by comparing its results with those obtained in parallel with a standard chair side culture method. The described method enables a rapid and exact determination of unknown amounts of S. mutans and could provide an efficient tool for evaluating the caries risk in a patient and to monitor the efficiency of preventive and therapeutic measures.