Comparison of Techniques for Measuring the Isoniazid Resistance of Tubercle Bacilli

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Abstract
Sensitivity tests of isoniazid-resistant tubercle bacilli on Lowenstein medium containing a range of isoniazid concns. showed a marked fall in resistance when the organisms were subcultured on Dubos medium. There was a good correlation in the results of sensitivity tests with Lowenstein and Dubos media containing isoniazid in various concns. of the organisms grown, but not with organisms grown on Lowenstein medium. Although not entirely satisfactory, Lowenstein medium was better than Dubos medium for the growth of the resistant strains. Storage at 37[degree]C, dilution and subculture reduced their resistance.