Evaluation of streptomycin and ethambutol concentrations for susceptibility testing of Mycobacterium tuberculosis by radiometric and conventional procedures.

Clinical isolates of Mycobacterium tuberculosis were used to compare various concentrations of streptomycin and ethambutol in the BACTEC 460 (Johnston Laboratories, Inc., Towson, Md.) radiometric method for drug susceptibility testing with those in the conventional method. Streptomycin used at 2.0 micrograms/ml for both methods showed a 0.99 agreement with susceptible strains and a 0.97 agreement with resistant strains. Ethambutol used at 2.5 micrograms/ml for the radiometric method showed 1.00 agreement with both susceptible and resistant strains when compared with ethambutol at 5.0 micrograms/ml for the conventional method.