Department of Food Hygiene and Environmental Health, Faculty of Veterinary Medicine, University of Helsinki, P,O, Box 66, Agnes Sjöbergin katu 2, FI-00014, Helsinki, Finland.
Vet Res. 2013 Jul 16;44(1):56. doi: 10.1186/1297-9716-44-56.
Genomic analysis of a metronidazole resistant H. bizzozeronii strain revealed a frame length extension of the oxygen-insensitive NAD(P)H-nitroreductase HBZC1_00960 (RdxA), associated with the disruption of the C-terminal cysteine-containing conserved region (IACLXALGK). This was the result of the extension (from C8 to C9) of a simple sequence cytosine repeat (SSCR) located in the 3' of the gene. A 3' SSCR is also present in the rdxA homolog of H. heilmannii sensu stricto, but not in H. pylori. We showed that in the majority of in vitro spontaneous H. bizzozeronii metronidazole resistant mutants, the extension of the 3' SSCR of rdxA was the only mutation observed. In addition, we observed that H. bizzozeronii ΔrdxA mutant strain showed the same MIC value of metronidazole observed in the spontaneous mutants. These data indicate that loss of function mutations in rdxA and in particular the disruption of the conserved region IACLXALGK is associated with reduced susceptibility to metronidazole in H. bizzozeronii. Slipped-strand mispairing of the SSCR located in the 3' of the H. bizzozeronii rdxA appears to be the main mechanism. We also observed that H. bizzozeronii acquires resistance to metronidazole at high mutation rate, and that serial passages in vitro without selection induced an increased level of susceptibility. In conclusion, contrary to what was previously described in H. pylori, the H. bizzozeronii rdxA appears to be a contingency gene which undergoes phase variation. The contingency nature of rdxA should be carefully considered when metronidazole is used in the treatment of H. heilmannii-associated gastritis.
对一株甲硝唑耐药的 H. bizzozeronii 菌株进行基因组分析发现，氧不敏感 NAD(P)H-硝基还原酶 HBZC1_00960（RdxA）的框架长度延长，这与 C 末端含半胱氨酸保守区（IACLXALGK）的破坏有关。这是由于基因 3' 处简单序列胞嘧啶重复序列（SSCR）的扩展（从 C8 到 C9）所致。H. heilmannii sensu stricto 的 rdxA 同源物中也存在 3' SSCR，但 H. pylori 中不存在。我们表明，在大多数体外自发甲硝唑耐药的 H. bizzozeronii 突变株中，仅观察到 rdxA 的 3' SSCR 扩展。此外，我们观察到 H. bizzozeronii ΔrdxA 突变株的 MIC 值与自发突变株观察到的甲硝唑值相同。这些数据表明 rdxA 的功能丧失突变，特别是保守区 IACLXALGK 的破坏，与 H. bizzozeronii 对甲硝唑的敏感性降低有关。位于 H. bizzozeronii rdxA 3' 的 SSCR 发生错配滑动可能是主要机制。我们还观察到 H. bizzozeronii 以高突变率获得对甲硝唑的耐药性，并且在没有选择的体外连续传代诱导了敏感性的增加。总之，与之前在 H. pylori 中描述的情况相反，H. bizzozeronii 的 rdxA 似乎是一个经历相位变异的备用基因。在使用甲硝唑治疗与 H. heilmannii 相关的胃炎时，应仔细考虑 rdxA 的备用性质。
