A selective medium for the isolation of Corynebacterium species in oral cavities

Corynebacterium matruchotii is a microbial inhabitant in the oral cavity of humans and is associated with the formation of dental calculi. C. matruchotii forms highly specific morphological units, which are referred to as corn-cobs. Although other Corynebacterium species have frequently been isolated from the oral cavity of humans, their distribution has not been reported as extensively. The aim of the present study was to develop a selective medium to isolate the genus Corynebacterium and examine the distribution Corynebacterium species in the oral cavity of humans. The growth recoveries of representative Corynebacterium species on the selective medium were sufficient. Moreover, the growth of other representative oral bacteria was markedly inhibited on the selective medium. The proportion of Corynebacterium species in saliva samples collected from 20 subjects was examined. PCR primers were designed for the oral Corynebacterium species. C. matruchotii and Corynebacterium durum accounted for 0.3% and 1.5% of the total cultivable bacteria number on the BHI medium from saliva samples, respectively. The selective medium could distinguish C. matruchotii from C. durum by each colony color using differences in acid production from galactose. The selective medium, designated OCM, was useful for isolating oral Corynebacterium species.