Drug sensitivity of tubercle bacilli is usually determined by the indirect method, because the direct method is not considered easy to obtain standardized inocula for tests. Therefore, the present study has stressed on the standardization of inoculum size for the direct ,sensitivity test. In order to determine probable number of culturable bacilli in the suptum specimen, we used the fluorescence microscope instead of conventional light microscope, because we could scan much larger fields of smear in a much shorter time by the former than by the latter. Microscopic enumeration of acid-fast bacilli in the sputum specimen was compared with the number of colony forming particles on culture examination and we could
prepare a proper inoculum by diluting the digested sputum on the basis of microscopic data. If the homogenized sputa contain more then 100 or 50 to 100 bacilli per fluorescence microscopic field, it is desirable to dilute the specimens in 10 or 5 folds respectively before inoculation. If the specimens contain more than 100 bacilli per smear or 1 to 50 bacilli per microscopic field, the specimens must be planted onto media without dilution or after 2 folds dilution. Minimal inhibitory concentrations(MIC) of tubercle bacilli to KM, EMB, TH, and CS showed a great differences between Lowenstein-Jensen medium and KIT medium, regardless of the methods employed. In the indirect methods, the minimal inhibitory concentrations to INH and SM were higher in KIT medium than those in Lowenstein- Jensen medium. But it was not evident in the direct method.
|