Conditions that may affect the results of susceptibility testing of Mycobacterium tuberculosis to pyrazinamide
Conditions that may affect the results of susceptibility testing of Mycobacterium tuberculosis to pyrazinamide
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DOI：
10.1099/0022-1317-51-1-42
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发表时间：
2002-01-01
影响因子：
3
通讯作者：
Sun, ZH
中科院分区：
文献类型：
--
作者：
Zhang, Y;Permar, S;Sun, ZH
吡嗪酰胺（Pyrazinamide， PZA）是一种重要的一线抗结核药物，仅在酸性pH下起作用，但酸性pH给PZA药敏试验带来了很大困难。PZA检测的一个常见问题是由大细菌接种引起的假耐药。本研究探讨了假耐药与细菌数量、细菌坑及其他可能影响PZA易感性的因素之间的关系。大剂量接种（1014芽孢杆菌/ml）使结核分枝杆菌H37Ra的培养基坑由5.5向中性显著增加，从而产生假耐药结果。培养基pH的增加被确定为活杆菌的作用；热杀杆菌作用很小或没有作用。对PZA及其活性衍生物吡嗪酸（POA）的敏感性在7H11琼脂培养基上相当，但在含有牛血清白蛋白（BSA）的液体培养基中，POA的活性低于PZA，表明BSA存在时，PZA或POA的敏感性降低，这是因为BSA对培养基的中和作用和显著的POA结合。3个月大的H37Ra培养比4天的培养对PZA暴露更敏感，这表明PZA对未生长的杆菌更有活性。最后，POA外排泵抑制剂利血平即使在接近中性pH 6.8时也会增加PZA的敏感性，其MIC为400 mg/L，与未使用利血平的1000 mg/L相比。这些发现对了解PZA的作用方式和PZA的药敏试验具有重要意义。
Pyrazinamide (PZA) is an important front-line anti-tuberculosis drug that is active only at acid pH. However, acid pH causes significant difficulty for PZA susceptibility testing. A common problem in PZA testing is false resistance caused by large bacterial inocula. This study investigated the relationship of false resistance to numbers of bacilli, pit and other factors that potentially affect susceptibility to PZA. Large inocula (1014 bacilli/ml) of M. tuberculosis H37Ra caused significant increase in medium pit from 5.5 towards neutrality, and thus produced false resistance results. The increase in medium pH was determined to be a function of live bacilli; heat-killed bacilli had little or no effect. Susceptibility to PZA and its active derivative pyrazinoic acid (POA) was comparable on 7H11 agar medium, but POA was less active than PZA in liquid medium containing bovine serum albumin (BSA), suggesting that susceptibility to PZA or POA was reduced in the presence of BSA, because of its neutralising effect on medium pit and significant POA binding. A 3-month-old H37Ra culture was shown to be more susceptible to PZA exposure than a 4-day log-phase culture, suggesting that PZA is more active for non-growing bacilli. Finally, reserpine, an inhibitor of POA efflux pump, increased susceptibility to PZA even near neutral pH 6.8, with an MIC of 400 mg/L compared with 1000 mg/L without reserpine. These findings should have implications for understanding the mode of action of PZA and for PZA susceptibility testing.