Jorgensen M A, Manos J, Mendz G L, Hazell S L
School of Microbiology and Immunology, University of New South Wales, Sydney, Australia.
J Antimicrob Chemother. 1998 Jan;41(1):67-75. doi: 10.1093/jac/41.1.67.
The effects of metronidazole on catalase-positive and spontaneous catalase-negative mutants of Helicobacter pylori were studied to investigate whether the action of metronidazole on this microaerophilic organism occurs by reactive oxygen species generated by futile cycling or by the reduction of metronidazole to its active form. Increased sensitivity would be expected to occur in catalase-negative mutants if the mode of action of metronidazole was mediated through reactive oxygen species that may result from futile cycling of metronidazole. Two strains, RU1 and N6, were found to mutate spontaneously to a catalase-negative phenotype. The catalase-positive strain RU1(KatA+) and its catalase-negative counterpart RU1(KatA-) were sensitive to metronidazole, with MICs of 0.5 mg/L. The metronidazole-sensitive strain RU1(KatA-) lost viability at a rate similar to the parent RU1(KatA+) strain in the presence of 10 mg/L of metronidazole. Stable resistance to metronidazole was induced in RU1(KatA+) and RU1(KatA-) by passaging these strains in the presence of metronidazole. The catalase-positive and catalase-negative strains, N6(KatA+) and N6(KatA-), were resistant to metronidazole, with MICs of 96 mg/L. These observations indicated that the presence or absence of catalase activity did not affect the susceptibility of strains to metronidazole. The metabolism of metronidazole by H. pylori was investigated by 14N-NMR spectroscopy. Metronidazole was reduced in sensitive, catalase-positive and catalase-negative strains. Metronidazole-resistant cells reduced the 5-nitroimidazole more slowly, suggesting that resistance is achieved through the prevention or inhibition of metronidazole reduction.
研究了甲硝唑对幽门螺杆菌过氧化氢酶阳性和自发过氧化氢酶阴性突变体的影响，以调查甲硝唑对这种微需氧菌的作用是通过无效循环产生的活性氧还是通过甲硝唑还原为其活性形式来实现的。如果甲硝唑的作用方式是通过甲硝唑无效循环可能产生的活性氧介导的，那么过氧化氢酶阴性突变体预计会表现出更高的敏感性。发现两个菌株RU1和N6自发突变为过氧化氢酶阴性表型。过氧化氢酶阳性菌株RU1（KatA +）及其过氧化氢酶阴性对应菌株RU1（KatA -）对甲硝唑敏感，MIC为0.5mg/L。在10mg/L甲硝唑存在下，对甲硝唑敏感的菌株RU1（KatA -）的活力丧失速率与亲本RU1（KatA +）菌株相似。通过在甲硝唑存在下传代这些菌株，在RU1（KatA +）和RU1（KatA -）中诱导出对甲硝唑的稳定抗性。过氧化氢酶阳性和过氧化氢酶阴性菌株N6（KatA +）和N6（KatA -）对甲硝唑耐药，MIC为96mg/L。这些观察结果表明，过氧化氢酶活性的有无并不影响菌株对甲硝唑的敏感性。通过14N-NMR光谱研究了幽门螺杆菌对甲硝唑的代谢。甲硝唑在敏感的、过氧化氢酶阳性和过氧化氢酶阴性菌株中被还原。耐甲硝唑的细胞还原5-硝基咪唑的速度较慢，这表明耐药性是通过阻止或抑制甲硝唑的还原而实现的。
