Isolation of Streptococcus mutans in the gastrointestinal tract of corpses

Objective The oral–gut axis, the pathway by which oral bacteria reach the intestine, has recently attracted attention. However, no recent studies have isolated live Streptococcus mutans, a major pathogen of dental caries, in the gastrointestinal tract. In the present study, we isolated S. mutans from the gastrointestinal tract of corpses.Methods Fifty corpses from forensic autopsies (ages 0–94 years, median age 49) were used. Samples were taken from the oral cavity and gastrointestinal tract (esophagus, stomach, duodenum, small intestine, and large intestine) using sterile swabs. S. mutans isolates was cultured from the swabs, and DNA and RNA of the bacteria were extracted for genetic analysis.Results S. mutans was isolated from each organ with the following frequency: oral cavity, 14 cases (28%); esophagus, 3 cases (6%); stomach, 1 case (2%); duodenum, 0 cases (0%); small intestine, 1 case (2%); and large intestine, 4 cases (8%). When S. mutans strains isolated from the oral cavity and gastrointestinal tract of the same corpses were compared, the serotypes and genotypes were completely consistent. Bioinformatic analysis showed that gene expression and predicted functions differed between S. mutans strains isolated from the oral cavity and the gastrointestinal tract, even though these S. mutans strains were the same genotype.Conclusion These results suggest that S. mutans strains existing in the gastrointestinal tract may undergo changes in gene expression to adapt to the environment of each organ.