Comparison of various measures of sensitivity of M. tuberculosis to ethambutol.
Subbammal, S.; Nair, N.G.K.; Radhakrishna, S.; Tripathy, S.P.
Tubercle; 1978; 59; 185-191.
A sensitivity test for ethambutol was standardised, and performed on cultures isolated from patients before and after the start of chemotherapy with ethambutol and isoniazid. A discrimination type of approach was employed and three criteria of resistance were evolved: (a) growth of 20 colonies or more on ethambutol 4 µg/ml, using a standard inoculum; (b) a proportion of 25% or more on ethambutol 1.4 µg/ml; (c) a proportion of 5% or more on ethambutol 2 µg/ml. The MIC definition appears to be the best in view of its simplicity and insensitivity of the classification (as sensitive or resistant) to variations in inoculum size.
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