Characterization of Streptococcus mutans in a Dental College Population

Objectives: Streptococcus mutans (SM) is known to play a significant role in the development of dental caries. The objective of this project is to isolate SM from dental plaque collected from students at the University of Iowa College of Dentistry and conduct an analysis of SM genotypes detected in this relatively caries-free population. Through this project, we have begun to compile a library of SM strains from healthy subjects for potential future comparison to strains detected in populations with high rates of decay.
Methods: Sterile cotton swabs were used to collect whole mouth plaque samples from 18 students in the class of 2020 at the University of Iowa College of Dentistry. Samples were diluted and spiral plated onto MSKB (Mitis salivarius-Kanamycin-Bacitracin) agar for SM counts and isolation.. Identification of presumed SM isolates was confirmed by colony morphology and PCR targeting the gtfB gene. Genotyping was completed by AP-PCR (OPA2 primer). GelComparIIv6.5 software was used to analyze gels and create dendograms for isolate comparison.
Results: SM was detected in 66% (12/18) of students in this study. Only 3 SM genotypes were identified in this population. Individual subjects showed a range of 0-2 genotypes of SM, with genotypes A, B, and C present in 11% (2/18), 5.5% (1/18), and 61% (11/18) respectively. Two individuals of all subjects were colonized by 2 different genotypes.
Conclusions: Our results demonstrate relatively low diversity in SM genotypes with only 11% of subjects colonized by more than one genotype, and 33% with no SM present in this dental student population. This library of SM strains found in healthy subjects will be beneficial for future comparison to what is found in populations with much higher risk and incidence of caries.