Use of microtiter plate to drug susceptibility testing for Mycobacterium tuberculosis
has been evaluated in the hope of replacing it with the conventional method, which is
so complex, laborious, and time-consuming that it requires more materials, equipments,
and skilled technieque.
The results obtained were summarized as follows.
1) Drug susceptibility testing with 240 isolates of M. tuberculosis using
Lowenstein-Jensen medium showed 97.5% agreement of the results between two
methods for kanamycin (KM) and rifampicin (RMP), 93.8% for streptomycin (SM),
92.9% for isoniazid (INH), 91.7% for ρ-aminosalicylic acid (PAS), and 89.6% for
ethambutol (EMB). In a separate study with 38 strains using 10-1 ㎎/㎖ of
inoculum, overall agreement was 100% for all drugs tested.
2) The direct susceptibility tests with 10 sputum specimens, that had been digested,
decontaminated, concentrated by centrifugation, and then directly inoculated on the drug
free and containing media, showed 100% agreement between two methods for EMB,
ethionamide (TH), INH, RMP, SM, and tuberactionmycin (TUM), and 90% for CS, KM,
and PAS.
3) Agreement was very poor between two tests for pyrazinamide (PZA), which had
been done in acidic medium.
Microtiter method is easy and rapid to perform and requires less amount of medium,
merely one-tenth of the conventional method and no culture bottles or tubes. In addition,
it is possible to shorten incubation period providing an average gain of 2 weeks or so.
As the result of this study, microtiter method seems to be applicable for routine use
except for PZA if the inoculum size and incubation period are well standardized.
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