Novel Selective Medium for the Isolation of Rothia aeria, Which Is an Inhabitant of the Human Oral Cavity

Abstract

Roth aeria, Rothia dentocariosa, and Rothia mucilaginosa are isolated from the human oral cavity. Among them, R. aeria can cause severe systemic infection diseases (e.g., bronchitis, endocarditis, pneumonia, and sepsis). However, the veritable prevalence of this organism in the human oral cavity has not ever been known. Thus, the selective medium for the isolation and quantification of R. aeria is necessary to assess the prevalence of this organism, and to diagnose various R. aeria infection diseases. To investigate R. aeria distribution in oral cavities, a novel selective medium (RAESM) was developed for isolating and quantifying R. aeria. RAESM consists of sodium gluconate, tryptone, meat extract, sodium fluoride, acriflavin neutral, fosfomycin, lincomycin, colistin, aztreonam, and agar. Polymerase chain reaction (PCR) primers were designed based on partial sequences of the 16S rDNA genes of R. aeria. The percentage of R. aeria in saliva samples collected from 20 subjects was examined. Moreover, we examined the antibiotic susceptibility of thirty isolates from six subjects. The average growth recovery of R. aeria on RAESM was 96.6% compared with that on Brain Heart Infusion supplemented with Yeast Extract (BHI-Y) agar. Growth of other representative oral bacteria, including other Rothia species, was remarkably inhibited on the selective medium. The PCR primers reacted to R. aeria and did not react to other Rothia species or representative oral bacteria. R. aeria was detected as 1.0% of the total bacteria, 5.9×107CFU/ml, on BHI-Y agar in the oral cavities of all subjects. R. aeria isolates obtained in this study were susceptible to most antibiotics; however R. aeria isolates from one subject were highly resistant to erythromycin, lincomycin, and clindamycin. R. aeria may be a part of the normal flora in the human oral cavities. A novel selective medium, RAESM, was useful for isolating R. aeria. Moreover, it was indicated that RAESM was useful for diagnosing R. aeria infections.