Genetic diversity within Streptococcus mutans evident from chromosomal DNA restriction fragment polymorphisms

Area of Science:

• Microbiology
• Genetics
• Infectious Diseases

Background:

• Studying the natural history of Streptococcus mutans infections is challenging due to limitations in current phenotypic typing methods.
• Most mutans streptococci linked to dental caries belong to biotype I (S. mutans), making isolate differentiation difficult with existing techniques.

Purpose of the Study:

• To develop and validate a novel genomic fingerprinting method for distinguishing individual Streptococcus mutans isolates.
• To investigate the transmission patterns and natural history of S. mutans infections in mother-infant pairs using this new technique.

Main Methods:

• Genomic fingerprinting of S. mutans strains by analyzing chromosomal DNA digested with restriction endonuclease HaeIII.
• Examining restriction fragment profiles of S. mutans isolates from three mother-infant pairs during infant colonization.
• Assessing strain stability over a 3-year period in one mother-infant pair.

Main Results:

• Unique DNA restriction fragment profiles (fingerprints) were observed for S. mutans strains from over 30 individuals.
• Infant S. mutans isolates showed identical restriction fragment profiles to their mothers', indicating maternal transmission.
• Identical S. mutans restriction profiles were stably maintained for up to 3 years in a mother-infant pair.
• Mothers and infants typically harbored only a few S. mutans strains, suggesting transmission is limited to family cohorts.

Conclusions:

• Genomic fingerprinting provides a powerful tool for studying the acquisition and transmission of Streptococcus mutans.
• Maternal transmission is a significant route for S. mutans colonization in infants.
• Streptococcus mutans transmission appears to occur within discrete family units, with strains persisting over time.