McIver Christopher, Hogan Tiffany, White Peter, Tapsall John
Department of Microbiology (SEALS), Prince of Wales Hospital, Randwick, NSW, Australia.
Pathology. 2004 Apr;36(2):166-9. doi: 10.1080/00313020410001672019.
To investigate the diversity of genetic mutation in the quinolone resistance-determining region (QRDR) of gyrA in clinical isolates and laboratory-derived mutants of Campylobacter jejuni resistant to ciprofloxacin (CipR) and to determine the influence of this mutation on the susceptibility of the organisms to different quinolone antibiotics.
Laboratory-derived CipR mutants were obtained from C. jejuni NCTC 11 168 and six quinolone-sensitive faecal isolates (parent prototypes) grown in sub-inhibitory concentrations of ciprofloxacin. Initial mutants found to be CipR were designated 'primary mutants' and subjected to a repeat of this process to select 'secondary mutants' with increased resistance. The susceptibility of the mutants and an additional six clinical isolates of CipR C. jejuni to seven quinolone antibiotics was determined by measuring their MICs. The QRDR of gyrA in all strains was amplified by PCR, sequenced and compared with that of the L04566 C. jejuni gyrA gene.
All six CipR clinical isolates contained a Thr-86-Ile mutation. This was also the commonest mutation found amongst the laboratory derived CipR strains. Other derived mutations in the in vitro derived CipR group included Asp-90-Asn, Thr-86-Ala, and a previously unreported double mutation, Asp-85-Tyr and Thr-86-Ile. Strains with the Thr-86-Ile mutation had the highest MICs to seven different quinolones. CipR strains with other single mutations had a lower range of MICs. There were no additional QRDR mutational changes detected in secondary mutants even where MICs to the fluoroquinolones were higher than in primary mutants.
Thr-86-Ile mutations were common in both clinical and laboratory derived CipR strains. Other mutations found amongst the latter strains were more sensitive to the fluoroquinolones. Different QRDR changes in gyrA differentially affected the susceptibility of CipR C. jejuni to the various fluoroquinolones.
研究空肠弯曲菌临床分离株及环丙沙星耐药实验室突变株中gyrA喹诺酮耐药决定区(QRDR)的基因突变多样性,并确定该突变对菌株对不同喹诺酮类抗生素敏感性的影响。
从空肠弯曲菌NCTC 11168及6株在亚抑菌浓度环丙沙星中生长的喹诺酮敏感粪便分离株(亲本原型)获得实验室衍生的环丙沙星耐药(CipR)突变株。最初发现的CipR突变株被指定为“初级突变株”,并重复此过程以选择耐药性增加的“次级突变株”。通过测量突变株及另外6株CipR空肠弯曲菌临床分离株对7种喹诺酮类抗生素的最低抑菌浓度(MIC)来确定其敏感性。通过聚合酶链反应(PCR)扩增所有菌株中gyrA的QRDR,进行测序并与空肠弯曲菌L04566 gyrA基因进行比较。
所有6株CipR临床分离株均含有Thr-86-Ile突变。这也是在实验室衍生的CipR菌株中发现的最常见突变。体外衍生的CipR组中的其他衍生突变包括Asp-90-Asn、Thr-86-Ala,以及一个先前未报道的双突变Asp-85-Tyr和Thr-86-Ile。具有Thr-86-Ile突变的菌株对7种不同喹诺酮类药物的MIC最高。具有其他单突变的CipR菌株的MIC范围较低。即使对氟喹诺酮类药物的MIC高于初级突变株,在次级突变株中也未检测到额外的QRDR突变变化。
Thr-86-Ile突变在临床和实验室衍生的CipR菌株中均很常见。在后者菌株中发现的其他突变对氟喹诺酮类药物更敏感。gyrA中不同的QRDR变化对CipR空肠弯曲菌对各种氟喹诺酮类药物的敏感性有不同影响。