Clinical and genetic analysis of oral and nasal staphylococcus aureus isolates in dental patients

Staphylococcus aureus is a common bacterium that sometimes causes various pyogenic diseases. Methicillin resistant S. aureus (MRSA) infections are particularly difficult to treat. Recently, MRSA has been spreading in the community, so it is important to determine the prevalence of MRSA in the community and to conduct epidemiological studies from genetic and statistical perspectives. In this study, S. aureus/MRSA was isolated from the oral and nasal cavities of 504 dental patients (65 inpatients and 439 outpatients). Sixty-two S. aureus strains and 9 MRSA strains were isolated from the oral cavity, and 112 S. aureus strains and 21 MRSA strains were isolated from the nasal cavity. Multi-locus sequence typing (MLST) analysis showed ST8 was high (18 isolates) among 30 MRSA isolates, whereas among 144 methicillin sensitive isolates, ST15 (25 isolates) and ST8 (20 isolates) were high. Statistical analysis of the patients' clinical status revealed a correlation between oral S. aureus and denture use. Among the 34 patients from whom S. aureus was isolated from both sites, 25 had the same ST, and 23 showed below 40 single-nucleotide polymorphisms which are considered to be identical strains. Our study revealed various properties of S. aureus/MRSA in the oral and nasal cavities as commensals.