Isolation and Drug Susceptibility of Streptomycin Sensitive Taylorella equigenitalis from Mares with Metritis and Infertility in Japan

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During the 1985 breeding season, Taylorella equigenitalis was isolated from 33 of 478 cervical swabs taken from mares with metritis and infertility in a breeding area of Hokkaido, the northernmost part of Japan. Contagious equine metritis (CEM) broke out in this aera for the first time in the 1980 breeding season. When 25 of these isolates at the 2nd passage level were examined by the disk diffusion test using commercial discs with 50μg of streptomycin (SM), 4 were susceptible to SM and 21 resistant. After the 3rd subculture the minimal inhibitory concentration (MIC) was 12.5μg/ml for 90% of SM-sensitive strains and 200μg/ml for 90% of SM-resistant strains. After the 4th subculture, however, it became 200μg/ml for 90% of SM-sensitive strains. There was no difference in susceptibility to any other antimicrobial agents between the SM-sensitive and SM-resistant strains. These results suggest that the MIC of SM to the sensitive strains of T. equigenitalis may be less than 12.5μg/ml at the time of primary isolation and increase quickly to 200μg/ml after several subcultures on media without SM. So these strains differ from SM-sensitive strains of other bacteria in an appearance of resistance to SM. For the purpose of control and eradication of CEM, it is absolutely necessary to use media without SM for the selective isolation of any strain of T. equigenitalis from carrier horses of the disease.
日本ウマ科学会の論文