DRUG SENSITIVITY-RESISTANCE DETERMINATION AND SIMPLE ENZYMATIC TESTS FOR THE DIFFERENTIATION OF MYCOBACTERIA.

Tests to determine mycobacterial sensitivity to antituberculosis drugs have become a routine procedure to enable clinicians to apply the most suitable treatment. However, while antimycobacterial drugs have been widely and successfully used in recent years, laboratory techniques for performing drug sensitivity tests have not yet been standardized and thus do not permit international comparison of results.Among the main hindrances to standardization are differences in the sensitivity of culture media, the capacity of some of the ingredients to adsorb certain drugs, the decomposition of some drugs when exposed to high temperatures during coagulation of solid media, and difficulties in the preparation of standard inocula.The techniques described in this paper have been used with success to determine the sensitivity to the three major antituberculosis drugs (isoniazid, streptomycin and p-aminosalicylic acid) of 600 strains of mycobacteria isolated from 200 newly diagnosed cases in a WHO-sponsored field trial. In all these patients, sputum conversion was achieved by treatment with a combination of the three drugs, without the emergence of resistant strains.The cytochemical tests recommended by the authors for routine use in the differentiation of mycobacteria are a combined test for catalase and peroxidase activity and either the niacin test or, preferably, the Virtanen-Griess nitrate test for differentiating Mycobacterium tuberculosis from Myco. bovis.