[Fluctuation in the ratio between drug-resistant and -susceptible M. tuberculosis bacilli which were isolated from patients with prolonged anti-tuberculosis treatment].

Purpose: In this study, we examined the fluctuation in the ratio between strains of tuberculosis bacilli resistant and susceptible to the anti-tuberculosis drugs.

Material & Method: We selected the cases in which the bacilli acquired drug resistance during the therapy and the cases in which drug resistance was fluctuating during prolonged anti-tuberculosis treatment. We selected the isolates throughout the medication period, and the selected isolates were separated into respective single colonies. Then we measured the minimal inhibitory concentration (MIC) for each colony by microdilution test for M. tuberculosis complex, BrothMIC MTB-1 (Kyokuto Pharmaceutical Inc., Tokyo).

Results: Five patients were eligible for analysis because their medical histories were clearly recorded and drug resistance changed during the course. The MIC of 19 isolates, 202 colonies were measured. Isolates with coexisting drug-resistant and -susceptible colonies were detected in 2 patients. From these results, we considered that the fluctuation in the ratio between drug-resistant and -susceptible bacilli changes with the progression of anti-tuberculosis medication.

Conclusion: We showed in this article that the drug-resistant bacilli increased rapidly when the strains acquired the drug resistance during medication, and when the administration of particular anti-tuberculosis drug was stopped, the susceptible bacilli seemed to increase gradually. However, the strain immediately became fully drug-resistant when the particular antibacterial drug was readministered.