Prevalence of Specific Streptococcus mutans strains in Non-alcoholic Steatohepatitis Patients

Objectives: Non-alcoholic fatty liver disease (NAFLD), the most common form of chronic liver disease in many industrialized countries, represents a wide spectrum of conditions ranging from non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH). Recently,Streptococcus mutans species harboring collagen-binding protein (Cnm) and protein antigen (PA) (Cnm- and PA-positive S. mutans) were shown to aggravate NASH in mice. Here, we assessed oral samples obtained from NAFLD patients with NASH or NAFL to determine the presence of Cnm-and PA-positive S. mutans strains.
Methods: Saliva samples were collected from 41 biopsy-proven NAFLD patients (21 with NASH, 20 with NAFL), then S. mutans strains were isolated and inoculated onto Mitis-Salivarius agar plates, and the number of colonies were determined. Genomic DNA was then extracted from each isolated strain and PCR performed to detect the cnmgene encoding Cnm, while PA expression was confirmed by Western blotting. This study was conducted after receiving approval from the ethics committees of Nara City Hospital, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, and Osaka University Graduate School of Dentistry.

Results: S. mutans strains were isolated from samples obtained from 80.9% of the NASH and 85.0% of the NAFL patients, which was not significantly different. As for Cnm- and PA-positive S. mutans strains, those were significantly more prevalent in the NASH patients (52.9% vs. 17.6%, P<0.05). In addition, the mean number ofS. mutans organisms in saliva from the NASH patients was significantly higher as compared to that from the NAFL patients (9.5×10⁵vs. 1.2×10⁴CFU/mL,P<0.05).

Conclusions: These results suggest that specific S. mutans species, such as Cnm- and PA-positive strains, are associated with the pathogenesis of NASH aggravation.