Anthony Richard M, den Hertog Alice, Mansjö Mikael, Werngren Jim
Center for Infectious Diseases Research, Diagnostics and Perinatal Screening (IDS), Center of Epidemiology and Surveillance of infectious diseases (EPI), National Institute for Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands.
Institute for Life Sciences and Chemistry, HU University of Applied Sciences Utrecht, Utrecht, The Netherlands.
Int J Mycobacteriol. 2016 Dec;5 Suppl 1:S71-S72. doi: 10.1016/j.ijmyco.2016.08.009. Epub 2016 Sep 20.
Pyrazinamide (PZA) is included in the 2016 World Health Organization multidrug-resistant tuberculosis treatment guidelines and is a key component of most ongoing clinical trials investigating novel antibiotic combinations. PZA resistance is associated with worse tuberculosis treatment outcomes. Unfortunately, for such an important drug, phenotypic susceptibility testing is extremely challenging. The exacting bacterial growth conditions required to induce susceptibility to the drug reduce the accuracy of the susceptibility assay, even in experienced laboratories, and widespread testing is not performed. This situation is unacceptable for such a valuable and important drug. A more complete understanding of the mechanism of action of PZA would be expected to lead to improvements in this situation. Although the exact mechanism of action of PZA is not known yet, it is widely accepted that PZA is a prodrug requiring transformation to pyrazinoic acid, the active form, by the mycobacterial enzyme encoded by the pncA gene. Most clinical resistance indeed appears to be a result of a diverse range of mutations in this gene and sequencing of the pncA gene has been shown to have excellent predictive power for PZA resistance. The wider availably of pncA sequencing in combination with databases of the phenotypic implications of these mutations has helped make genetic testing for PZA resistance a practical proposition. For the past decades, it has been generally accepted that an extracellular low pH is required for PZA activity but work in our laboratory [1] and others [2] has recently challenged this assumption. Alternative bacterial stresses, apart from a reduced pH of the growth media (such as reduced temperature), can also induce a PZA-susceptible phenotype. The characterization of spontaneous in vitro-resistant pyrazinoic acid mutants selected under neutral pH conditions suggests a key role for the pantothenate/coenzyme A biosynthetic pathway. This has profound implications for the mechanism of action of PZA as well as potentially the bacterial population against which PZA is active in the host. These findings will be discussed as well as their implications for further research and the future of PZA susceptibility testing.
吡嗪酰胺（PZA）被纳入2016年世界卫生组织耐多药结核病治疗指南，并且是大多数正在进行的研究新型抗生素组合的临床试验的关键组成部分。PZA耐药与结核病治疗效果较差相关。不幸的是，对于这样一种重要药物，表型药敏试验极具挑战性。诱导对该药物敏感所需的严格细菌生长条件降低了药敏试验的准确性，即使在经验丰富的实验室也是如此，并且未进行广泛检测。对于这样一种有价值且重要的药物，这种情况是不可接受的。对PZA作用机制的更全面理解有望改善这种情况。虽然PZA的确切作用机制尚不清楚，但人们普遍认为PZA是一种前药，需要由pncA基因编码的分枝杆菌酶转化为活性形式的吡嗪酸。大多数临床耐药似乎确实是该基因各种突变的结果，并且已证明pncA基因测序对PZA耐药具有出色的预测能力。pncA测序与这些突变表型影响数据库的更广泛可用性有助于使PZA耐药的基因检测成为一个切实可行的方案。在过去几十年中，人们普遍认为PZA活性需要细胞外低pH，但我们实验室[1]和其他实验室[2]的研究最近对这一假设提出了挑战。除了生长培养基pH降低（如温度降低）之外，其他细菌应激也可诱导PZA敏感表型。在中性pH条件下选择的自发体外耐药吡嗪酸突变体的特征表明泛酸/辅酶A生物合成途径起关键作用。这对PZA的作用机制以及PZA在宿主体内具有活性的潜在细菌群体具有深远影响。将讨论这些发现及其对进一步研究和PZA药敏试验未来的影响。
