A New Selective Medium for Oral Streptococci in Dogs

Objectives: The purpose of the present investigation was to study the cultivable oral microflora of dogs with special attention to the genus Streptococcus which is predominantly exists in the human oral cavity and to examine the selectivity of Mitis Salivarius agar medium which is commonly use for detection of human oral streptococci. Also we developed a new selective medium for streptococci from dog oral cavity. Methods: Oral samples from 68 dogs were cultured on MS medium under candle jar conditions. The recovery of new selective medium was compared with that on MS using oral samples from dogs. Results: The predominant bacterial group on MS plates were gram- negative rods. Gram-positive rods and -negative cocci were grown on the medium at low levels. Selectivity of streptococci on MS medium was 20.2%. The ratios of streptococci against total cultivable bacteria were 2.0%. A new selective medium, designated MS-CAN-AE, was developed for the isolation of streptococci from dog oral cavity. The average growth recovery of laboratory and isolated strains from oral cavity of streptococci on MS-CAN-AE medium was 84.1% compared to that on MS medium. Gram-negative rods were grown rarely on MS-CAN-AE. The selectivity of MS-CAN-AE was 95.0% for samples. Mutans streptococci were never found in any dog. Conclusion: Streptococci constituted a small percentage of the normal bacterial flora in dog oral cavity. The new selective medium was highly selective for streptococci. MS-CAN-AE medium, to replace MS, for streptococci in dog oral cavity samples will be useful for determining the distribution of streptococci.This study was supported in part by a Grant-in-Aid for Systematic Research Grant of Nihon University (2004) and for FRONTIER 2003 from MEXT.