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Advisory Committee Chair

Noel K Childers

Advisory Committee Members

Stephen A Moser

R Douglas Watson

Thane Wibbels

Document Type

Dissertation

Date of Award

2016

Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences

Abstract

Dental caries is chronic global infectious disease. Streptococcus mutans are most frequently associated with dental caries. The goal of this work is to use molecular genotyping methods to investigate the genetic diversity and evidence for transmission of S. mutans for the epidemiological study of dental caries. It was first necessary to validate methods proposed in this study including choice of selective media, choice of multilocus sequence typing (MLST) scheme, and the frequency of clonality. Analysis included 13,906 S. mutans isolates obtained from oral samples collected from children and their household members in an 8-year longitudinal epidemiological study. Two genotyping methods were used: Repetitive extragenic palindromic PCR (rep-PCR), a cost effective, rapid gel based typing method, differentiated by short, non-coding repetitive elements interspersed throughout the genome; and MLST, a molecular sequence based approach that differentiates strains based on 8 highly conserved housekeeping genes. Both methods are standardized, reproducible within and between laboratories, with web-based analysis tools for global data sharing. Results indicated that choice of media and MLST typing scheme were valid. Clonality of S. mutans was observed to be a characteristic of this population and a reference rep-PCR library for S. mutans was established. While 63% of children shared at least 1 genotype with their mothers, 72% of genotypes were not shared with any household family members. Rep-PCR was reasonably accurate at predicting strains of S. mutans requiring additional analysis with MLST. MLST analysis of the diverse genotype (G12) suggests that younger children share strains with their mother. Some strains of S. mutans appear to be highly transmissible and probable source individuals were identified. This work contributes to the understanding of S. mutans genotype diversity and its association with dental caries through molecular analysis approaches. These findings offer new insights into the genotypic distribution of strains using rep-PCR and MLST. The importance of child-to-child transmission is clearly demonstrated, although more validation with another method, such as MLST or whole genome sequencing is needed. Continued study of this data offers the potential for new understanding of how and which S. mutans strains contribute to the initiation and progression of dental caries.

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