[In-vitro susceptibility of Mycobacterium avium complex to isoniazid and ethionamide]

In this study, it was investigated whether or not Mycobacterium avium complex strains were inhibited by such low concentrations of isoniazid and ethionamide as possible in blood. The inhibitory concentrations were determined by the "Actual Count" method (Tsukamura, M.: Japan J. Tuberc. 12: 46-54, 1964), in which the inhibitory concentration was measured as a concentration that can inhibit the growth of 'countable' colony-forming units. The ratio of strains which were inhibited by such low concentrations as 0.2 microgram/ml isoniazid or 5 micrograms/ml ethionamide was 14%. The result suggests that there are some strains in which isoniazid or ethionamide are clinically effective, though their prevalence was low (14%).