Salfinger M, Heifets L B
National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Antimicrob Agents Chemother. 1988 Jul;32(7):1002-4. doi: 10.1128/AAC.32.7.1002.
The MICs of pyrazinamide (PZA) were determined for Mycobacterium tuberculosis cultivated under different pH conditions in 7H12 liquid medium. Mycobacterial growth was monitored by the radiometric method (BACTEC system; Johnston Laboratories, Inc., Towson, Md.). We observed a predictable eightfold difference between the MICs determined at pH 5.5 and those determined at pH 5.95. The highest MICs for 21 susceptible strains were 50.0 micrograms/ml at pH 5.5 and 400 micrograms/ml at pH 5.95. This eightfold difference enabled us to predict MICs at pH 5.5 from the values observed at pH 5.95. The use of 7H12 broth at pH 5.95 simplified the radiometric PZA susceptibility test by avoiding the addition of acid solutions in the course of cultivation, which was required when the test was performed at pH 5.5. An additional benefit of using pH 5.95 instead of pH 5.5 was that all tested strains grew at pH 5.95, while some of them, especially PZA-resistant strains, did not grow at pH 5.5.
在7H12液体培养基中，针对在不同pH条件下培养的结核分枝杆菌测定了吡嗪酰胺（PZA）的最低抑菌浓度（MIC）。采用放射性测量法（BACTEC系统；约翰斯顿实验室公司，马里兰州陶森）监测分枝杆菌的生长。我们观察到，在pH 5.5时测定的MIC与在pH 5.95时测定的MIC之间存在可预测的八倍差异。21株敏感菌株在pH 5.5时的最高MIC为50.0微克/毫升，在pH 5.95时为400微克/毫升。这种八倍差异使我们能够根据在pH 5.95时观察到的值预测pH 5.5时的MIC。使用pH 5.95的7H12肉汤简化了放射性PZA药敏试验，因为在培养过程中无需添加酸性溶液，而在pH 5.5进行试验时则需要添加。使用pH 5.95而非pH 5.5的另一个好处是，所有测试菌株在pH 5.95时均能生长，而其中一些菌株，尤其是耐PZA菌株，在pH 5.5时不能生长。
