Minimal inhibitory concentrations of isoniazid, rifampin, ethambutol, and streptomycin against Mycobacterium tuberculosis strains isolated before treatment of patients in Taiwan.

Minimal inhibitory concentrations (MICs) of isoniazid (INH), rifampin (RMP), ethambutol (EMB), and streptomycin (SM) for susceptible "wild" M. tuberculosis strains isolated from Taiwanese patients were within the limits previously reported for strains isolated in the United States. The highest agar-determined MICs (in 7H10 and 7H11 agar) corresponded well with the critical concentrations established for these media. The highest MICs found radiometrically in 7H12 broth were significantly lower than the critical concentrations proposed for this medium. On the basis of an evaluation of the highest broth-determined MICs found in this and in the previous study (1), we suggest that the following MICs, when determined radiometrically, should be used as breakpoints to classify the strain as "susceptible": for INH, 0.1 microgram/ml or less; for RMP, 0.5 microgram/ml or less; for EMB, 4.0 micrograms/ml or less; for SM, 2.0 micrograms/ml or less.