EFFECT OF ISONIAZID ON THE DEHYDROGENASE ACTIVITY OF MYCOBACTERIUM TUBERCULOSIS

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Abstract
Tubercle bacilli were exposed to various concentrations of isoniazid or alpha-ethyl-thioisonicotinamide for various times. The ability of the traated and untreated bacteria to reduce tetrazolium chloride was measured. The bacteria exposed to bactericidal concentrations of the drugs for 24 - 48 hours reduced tetrazolium at an accelerated rate and in larger amounts than the controls. After prolonged exposure to the drug, the bacteria lost this property. The enhancement of the dehydrogenase activity is attributed to a damaging effect of the drugs on the bacillary membranes and the hypothesis is discussed that the drug may inhibit the synthesis of a lipid constituent of the membranes of the tubercle bacillus.