Department of Clinical and Molecular Microbiology, University Clinical Hospital Centre Zagreb, Kišpatićeva 12, 10000 Zagreb, Croatia.
Institute of Clinical Microbiology, University of Szeged, Semmelweis u. 6, H-6725 Szeged, Hungary.
J Glob Antimicrob Resist. 2016 Jun;5:11-4. doi: 10.1016/j.jgar.2016.01.009. Epub 2016 Mar 4.
The aims of this study were to induce in vitro metronidazole resistance in nim-negative Bacteroides fragilis group strains and to determine the lactate dehydrogenase (LDH) activity of the induced strains. A collection of B. fragilis group strains were identified by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF/MS). Minimum inhibitory concentrations (MICs) for metronidazole were determined by the agar dilution technique. The presence of nim genes was screened by PCR. A sample of 52 nim-negative metronidazole-susceptible strains were selected at random and were exposed to metronidazole in the resistance induction experiment. LDH activity was measured by spectrophotometry. Of the 52 selected strains, 12 (23.1%) acquired resistance to metronidazole. MICs ranged from 8mg/L to 96mg/L. Eight of the twelve induced strains displayed decreased LDH activity, whilst only one expressed a significant increase in LDH activity with LDH values of 49.1U/mg and 222.0U/mg, respectively. In conclusion, in vitro induction of metronidazole resistance could be selected in nim-negative B. fragilis group strains. A statistically significant decrease in LDH activity was in contrast to previous findings in which, underlying higher metronidazole MICs, an increase in LDH activity compensated for the decreased activity of pyruvate-ferredoxin oxidoreductase (PFOR). These findings could be explained if the induction caused only physiological and not genetic changes. We believe that genetic mutations in the B. fragilis strain that demonstrated an emergent increase in LDH activity were responsible for the increased activity.
本研究的目的是诱导 nim 阴性脆弱拟杆菌群菌株产生体外甲硝唑耐药性，并测定诱导菌株的乳酸脱氢酶（LDH）活性。采用基质辅助激光解吸电离飞行时间质谱（MALDI-TOF/MS）对脆弱拟杆菌群菌株进行鉴定。采用琼脂稀释法测定甲硝唑的最小抑菌浓度（MIC）。通过 PCR 筛选 nim 基因的存在。随机选择 52 株 nim 阴性甲硝唑敏感株进行甲硝唑耐药诱导实验，采用分光光度法测定 LDH 活性。在 52 株选定的菌株中，有 12 株（23.1%）对甲硝唑产生了耐药性。MIC 范围为 8mg/L 至 96mg/L。12 株诱导株中有 8 株 LDH 活性降低，而只有 1 株 LDH 活性显著增加，分别为 49.1U/mg 和 222.0U/mg。结论：nim 阴性脆弱拟杆菌群菌株可在体外诱导甲硝唑耐药性。与之前的研究结果相反，在甲硝唑 MIC 值较高的情况下，LDH 活性的增加补偿了丙酮酸铁氧还蛋白氧化还原酶（PFOR）活性的降低。如果诱导只引起生理而非遗传变化，那么可以解释这些发现。我们认为，表现出 LDH 活性增加的脆弱拟杆菌株的基因突变是导致活性增加的原因。
