Heym B, Stavropoulos E, Honoré N, Domenech P, Saint-Joanis B, Wilson T M, Collins D M, Colston M J, Cole S T
Unité de Génétique Moléculaire Bactérienne, Institut Pasteur, Paris, France.
Infect Immun. 1997 Apr;65(4):1395-401. doi: 10.1128/iai.65.4.1395-1401.1997.
Mutations to the regulatory region of the ahpC gene, resulting in overproduction of alkyl hydroperoxide reductase, were encountered frequently in a large collection of isoniazid (INH)-resistant clinical isolates of Mycobacterium tuberculosis but not in INH-susceptible strains. Overexpression of ahpC did not seem to be important for INH resistance, however, as most of these strains were already defective for catalase-peroxidase, KatG, the enzyme required for activation of INH. Transformation of the INH-susceptible reference strain, M. tuberculosis H37Rv, with plasmids bearing the ahpC genes of M. tuberculosis or M. leprae did not result in a significant increase in the MIC. Two highly INH-resistant mutants of H37Rv, BH3 and BH8, were isolated in vitro and shown to produce no or little KatG activity and, in the case of BH3, to overproduce alkyl hydroperoxide reductase as the result of an ahpC regulatory mutation that was also found in some clinical isolates. The virulence of H37Rv, BH3, and BH8 was studied intensively in three mouse models: fully immunocompetent BALB/c and Black 6 mice, BALB/c major histocompatibility complex class II-knockout mice with abnormally low levels of CD4 T cells and athymic mice producing no cellular immune response. The results indicated that M. tuberculosis strains producing catalase-peroxidase were considerably more virulent in immunocompetent mice than the isogenic KatG-deficient mutants but that loss of catalase-peroxidase was less important when immunodeficient mice, unable to produce activated macrophages, were infected. Restoration of virulence was not seen in an INH-resistant M. tuberculosis strain that overexpressed ahpC, and this finding was confirmed by experiments performed with appropriate M. bovis strains in guinea pigs. Thus, in contrast to catalase-peroxidase, alkyl hydroperoxide reductase does not appear to act as a virulence factor in rodent infections or to play a direct role in INH resistance, although it may be important in maintaining peroxide homeostasis of the organism when KatG activity is low or absent.
在大量耐异烟肼（INH）的结核分枝杆菌临床分离株中，经常发现ahpC基因调控区发生突变，导致烷基过氧化氢还原酶过度产生，但在INH敏感菌株中未发现这种情况。然而，ahpC的过表达似乎对INH耐药性并不重要，因为这些菌株中的大多数过氧化氢酶-过氧化物酶KatG已经存在缺陷，而KatG是激活INH所需的酶。用携带结核分枝杆菌或麻风分枝杆菌ahpC基因的质粒转化INH敏感参考菌株结核分枝杆菌H37Rv，并未导致最低抑菌浓度（MIC）显著增加。在体外分离出H37Rv的两个高度耐INH的突变体BH3和BH8，结果显示它们不产生或仅产生少量KatG活性，就BH3而言，由于ahpC调控突变导致烷基过氧化氢还原酶过度产生，这种突变在一些临床分离株中也有发现。在三种小鼠模型中对H37Rv、BH3和BH8的毒力进行了深入研究：完全免疫 competent的BALB/c和C57BL/6小鼠、CD4 T细胞水平异常低的BALB/c主要组织相容性复合体II类基因敲除小鼠以及不产生细胞免疫反应的无胸腺小鼠。结果表明，产生过氧化氢酶-过氧化物酶的结核分枝杆菌菌株在免疫 competent小鼠中的毒力明显高于同基因KatG缺陷突变体，但当感染无法产生活化巨噬细胞的免疫缺陷小鼠时，过氧化氢酶-过氧化物酶的缺失就不那么重要了。在过表达ahpC的耐INH结核分枝杆菌菌株中未观察到毒力恢复，用适当的牛分枝杆菌菌株在豚鼠中进行的实验证实了这一发现。因此，与过氧化氢酶-过氧化物酶不同，烷基过氧化氢还原酶在啮齿动物感染中似乎不充当毒力因子，也不在INH耐药性中起直接作用，尽管当KatG活性低或不存在时，它可能对维持生物体的过氧化物稳态很重要。
