The in Vitro Effect of Antituberculous Agents in Relation to the Exposure Time on Ogawa Gly cerol Egg Medium.

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The in Vitro Effect of Antituberculous Agents in Relation to Drug-Exposure Time on Ogawa Glycerol Egg Medium.<BR>Here in Japan, Ogawa glycerol egg medium is now most frequently used for drug-sensitivity test of tubercle bacilli. However, little information has been available concerning the relation between drug exposure time and antibacterial effect on this me dium. This problem is directly concerned with the stability of potency of antituberculous drugs. In other words, if the decisive effect of test drugs is exerted upon the bacilli more rapidly than the potency-decreasing rate of the drugs, there will be little obstacles in the test. If the reverse is the case, however, the test result might be altered more or less. This state of affairs will not be the same depending upon the nature of drug effect (bactericidal or bacteriostatic) and also upon the drug concentration.<BR>The present authors examined the above problem using streptomycin (SM), isoniazid (INH), and PAS as test drugs. Namely, a time-course viabillity test was conducted by liberating the bacilli once inoculated upon drug-contaning Ogawa megium slants and then by reinoculating then upon fresh drug-free media. In this way, the bactericidal effect of the drugs was checked in relation to drug-exposure time. Two different methods were employed for liberation of the bacilli from drug envirorment. One of them was to homogenize the whole medium and dilute it by ten-fold steps so that the drug concentration might be low enough and the bacillary number might be adequate for subsequent colonial counting. The other method was to wash the surface of bacilli-inoculated media with a O.01 % solution of Triton WR-1339, and this washings and the serial ten-fold dilutions were used for viability test.<BR>Fig.1, 2, and Table 1 are the results a ccording to the former technique and Fig.3 and 4 are those according to the latter technique. Despite of the difference in technique, the results showed the same tendency. Namely, SM in the concentration of 4 mcg/ml and INH of 0.1 mcg/ml showed a marked bactericidal effect after only 3 day contact with bacilli inoculated onto Ogawa medium slants. On the other hand, the activity of PAS was proved mostly bacteriostatic.<BR>The observations gave us a suggestion as follows. The relation between drug-exposure time and antibacterial activity, which will be a factor in drugsensitivity test in association with the stability of drug potency, must be taken into our consideration especially concerning the bacteriostatic concentrations of SM and INH or in the case of essentially bacteriostatic drugs such as PAS, but it is not so vital problem concerning the bactericidal concentration of SM and INH.
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The in Vitro Effect of Antituberculous Agents in Relation to the Exposure Time on Ogawa Gly cerol Egg Medium.

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