Sato Toyotaka, Suzuki Yuuki, Shiraishi Tsukasa, Honda Hiroyuki, Shinagawa Masaaki, Yamamoto Soh, Ogasawara Noriko, Takahashi Hiroki, Takahashi Satoshi, Tamura Yutaka, Yokota Shin-Ichi
Department of Microbiology, Sapporo Medical University School of Medicine, Sapporo, Japan
Department of Microbiology, Sapporo Medical University School of Medicine, Sapporo, Japan.
Antimicrob Agents Chemother. 2017 Jan 24;61(2). doi: 10.1128/AAC.01654-16. Print 2017 Feb.
Tigecycline (TGC) is a last-line drug for multidrug-resistant Enterobacteriaceae We investigated the mechanism(s) underlying TGC nonsusceptibility (TGC resistant/intermediate) in Escherichia coli clinical isolates. The MIC of TGC was determined for 277 fluoroquinolone-susceptible isolates (ciprofloxacin [CIP] MIC, <0.125 mg/liter) and 194 fluoroquinolone-resistant isolates (CIP MIC, >2 mg/liter). The MIC and MIC for TGC in fluoroquinolone-resistant isolates were 2-fold higher than those in fluoroquinolone-susceptible isolates (MIC, 0.5 mg/liter versus 0.25 mg/liter; MIC, 1 mg/liter versus 0.5 mg/liter, respectively). Two fluoroquinolone-resistant isolates (O25b:H4-ST131-H30R and O125:H37-ST48) were TGC resistant (MICs of 4 and 16 mg/liter, respectively), and four other isolates of O25b:H4-ST131-H30R and an isolate of O1-ST648 showed an intermediate interpretation (MIC, 2 mg/liter). No TGC-resistant/intermediate strains were found among the fluoroquinolone-susceptible isolates. The TGC-resistant/intermediate isolates expressed higher levels of acrA and acrB and had lower intracellular TGC concentrations than susceptible isolates, and they possessed mutations in acrR and/or marR The MICs of acrAB-deficient mutants were markedly lower (0.25 mg/liter) than those of the parental strain. After continuous stepwise exposure to CIP in vitro, six of eight TGC-susceptible isolates had reduced TGC susceptibility. Two of them acquired TGC resistance (TGC MIC, 4 mg/liter) and exhibited expression of acrA and acrB and mutations in acrR and/or marR In conclusion, a population of fluoroquinolone-resistant E. coli isolates, including major extraintestinal pathogenic lineages O25b:H4-ST131-H30R and O1-ST648, showed reduced susceptibility to TGC due to overexpression of the efflux pump AcrAB-TolC, leading to decreased intracellular concentrations of the antibiotics that may be associated with the development of fluoroquinolone resistance.
替加环素（TGC）是治疗多重耐药肠杆菌科细菌的最后一线药物。我们研究了大肠杆菌临床分离株中TGC不敏感（TGC耐药/中介）的潜在机制。测定了277株对氟喹诺酮敏感的分离株（环丙沙星[CIP] MIC，<0.125 mg/L）和194株对氟喹诺酮耐药的分离株（CIP MIC，>2 mg/L）的TGC MIC。氟喹诺酮耐药分离株中TGC的MIC和MIC比氟喹诺酮敏感分离株高2倍（MIC分别为0.5 mg/L对0.25 mg/L；MIC分别为1 mg/L对0.5 mg/L）。两株氟喹诺酮耐药分离株（O25b:H4-ST131-H30R和O125:H37-ST48）对TGC耐药（MIC分别为4和16 mg/L），另外四株O25b:H4-ST131-H30R分离株和一株O1-ST648分离株显示中介结果（MIC，2 mg/L）。在氟喹诺酮敏感分离株中未发现TGC耐药/中介菌株。TGC耐药/中介分离株中acrA和acrB表达水平较高，细胞内TGC浓度低于敏感分离株，且acrR和/或marR存在突变。acrAB缺陷突变体的MIC明显较低（0.25 mg/L），低于亲本菌株。在体外连续逐步暴露于CIP后，8株TGC敏感分离株中有6株对TGC的敏感性降低。其中2株获得了TGC耐药性（TGC MIC，4 mg/L），并表现出acrA和acrB的表达以及acrR和/或marR的突变。总之，包括主要的肠道外致病谱系O25b:H4-ST131-H30R和O1-ST648在内的一群氟喹诺酮耐药大肠杆菌分离株对TGC的敏感性降低，原因是外排泵AcrAB-TolC的过度表达，导致抗生素细胞内浓度降低，这可能与氟喹诺酮耐药性的产生有关。
