Pyrazinamide is an effective drug against slowly multipling tubercle bacilli inside macrophages due to the acid environment. But it has been difficult to perform the susceptibility test of tubercle bacilli to this drug because pyrazinamide is inactive at the neutral pH of medium. Therefore, there still remain some problems to solve: how to determine an approprite pH of the medium maintaining active state of pyrazinamide and avoiding growth inhibition of test straits as few as possible and how to overcome the growth retard of organisms on culture media owing to the acid environment. Authors tried to examine all possible problems encountered with pyrazinamide susceptibility tests. We also compared the results of pyrazinamide susceptibility tests with simplified method of pyrazinamidase test recommended by Wayne, and both results obtained were analysed according to the history of chemotherapy. The results are summarized as follows;
1) The pH of medium greatly affected bacterial growth and most strains in logarithmic growth stage could usually grow on the media of preinspissation pH 4.8(pH 5.2 after inspissation) after 5-6 weeks’ cultivation.
2) Drug susceptibility patterns did not change any longer after 4 week-cultivation of H37Rv strains. Bacterial growth were restricted only to drug-free media at preinspissation pH 4.8 or lower in inoculum size of 10-1㎎ or at pH 5.0 or lower in 10-3㎎, but organisms normally grew at pH 5.2 or more even in the presence of high concentrations of PZA.
3) In 176 sprains from patients who have no history of previous antituberculous chemotherapy, 148 sprains(84.1%) possesed pyrazinamidase activity while 28 strains (15.9%) were devoid of it. All strains possessing pyrazinamidase activity were also confirmed as sensitive in pyrazinamide susceptibility tests, but in 28 strains of negative pyrazinamidase only 15 strains(53.6%) were resistant to pyrazinamide.
4) In 37 strains from patients with history of more than 6 months of pyrazinamide treatment, pyrazinainidase positives were 9 strains(24.3%) of which 8 straits were sensitive to pyraginamide. Twenty eight(75.7%) of 37 strains were pyrazinamidase negative, but only 18(64.8%) of 28 strains were resistant to pyrazinamide while the rest stowed differences in resistance depending on pH of media used.
5) Three-hundred ten strains were compare4 their pyrazinamide susceptibility with pyrazinamidase activity simultaneously. One-hundred sixty-one strains slowed at all preinspissation pH tested(pH 4.65, 4.85, and 5.05), but 64 strains crowed at pH 4.85 or higher, 35 strains growed at only pH 5.05, and the remaining could not grow at all pH used in susceptibility tests for pyrazinamide. Of 53 PZA sensitive strains at pH 4.85-5.05 among 141 acid untorelant strains, 45(84.9%) shoved positive pyrazinamidase by the Wayne method while 16 strains(66.7%) of 24 grown at only pH 5.05 were positive and 27 strains(63.4%) of 42 which did not grow at all pHs teated showed negative pyrazinamidase. In 169 acid tolerant strains which groved at pH 4.65-5.05, 101(83.5%) of 121 PZA sensitive strains at pH 4.65-5.05 possessed pyrazinamidase while 24(80.0%) of 30 P2A resistant at all acid media containing pyrazinamide could not hydrolyse pyrazinamide. It was noted that the results of tests for the pyrazinamide susceptibility and pyrazinamidase activity tended to fairly well correlated in the cased showing the same susceptibility or resistance patterns at all acid pHs used in tests.
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