Genotypic Diversities of American and Mexican Streptococcus mutans Clinical Isolates

Streptococcus mutans is consistently associated with dental caries initiation. Current literature suggests that the S. mutans population in children may be genetically diverse. Genetic identification currently involves a variety of approaches for clonal characterization. Strain relatedness as determined using genetic fingerprinting is an important epidemiological tool. Recent molecular diagnostics for mutans streptococci strain identification include: chromosomal DNA fingerprinting, pulsed-field gel electrophoresis, arbitrarily primed-polymerase chain reaction or randomly amplified polymorphic DNA, and ribotyping. These methods have their positive attributes, but can be costly and labor prohibitive. Another method, repetitive extragenic palindromic PCR (rep-PCR) has been used successfully in discriminating and genotyping strains of E. coli, Acinetobacter, Streptococcus pneumoniae and other bacterial species. However, this technology has not been applied to S. mutans genotyping. Objectives: This study investigated the usefulness of manual rep-PCR in genotyping S. mutans from U.S. and Mexican children using a primer set commonly used for other bacterial species. Methods: A commercial kit was used to isolate DNA from seventeen S. mutans clinical isolates, including UA159 (standard) and randomly selected clinical isolates from American and Mexican children. Extracted DNA was used to perform rep-PCR to screen several candidate primer pairs and various PCR buffers. Post amplification reactions were subjected to electrophoresis in 2% agarose gel and stained with ethidium bromide. Resulting banding patterns were compared within and between American and Mexican isolates. Results: Diverse banding patterns were seen within and between the American and Mexican isolates, although some banding patterns appeared identical. Conclusions: The results are consistent with previous findings concerning genetic stability in S. mutans. Further testing may reveal a useful and affordable manual rep-PCR alternative over a more expensive microfluidic method in S. mutans genotyping and be valuable in small-scale epidemiological studies of S. mutans colonization.

Supported by NIDCR grant DE016684