四环素诱导表皮葡萄球菌对氟喹诺酮类耐药性研究

目的　为研究氟喹诺酮类抗菌药物非特异性耐药机制建立细菌筛选方法,并研究其耐药特点及遗传稳定性。方法　使用高浓度四环素作诱导剂,分步诱导敏感表皮葡萄球菌产生高耐突变株,并从中选择对环丙沙星和司帕沙星耐药菌株。结果　经过4 步四环素诱导突变后,获得的突变株对四环素的M IC增加了500 倍,这些菌株中约有1/3 对环丙沙星和司帕沙星中度耐药,MIC比亲代株增加了60 倍。子代菌与亲代菌相比主要生化反应无改变,连续传代培养证明突变株对氟喹诺酮类药物的抗药性可稳定遗传。结论　采用四环素诱导突变的方法可使细菌获得对氟喹诺酮类的耐药性,提示用其它抗菌药物治疗感染失败的患者换用氟喹诺酮类药物时应慎重

Acquired fluoroquinolone resistance of Staphylococcus epidermidis induced by tetracycline

OBJECTIVE The purpose of this study was designed to select and grow fluoroquinolones resistant bacterial variants, which were suitable to study the mechanisms of non structure related fluoroquinolones resistance. METHODS The resistant clones were selected from 8 wild type Staphylococci epidermidis in the presence of tetracycline concentration up to 4 fold the MIC. The spontaneous resistant mutants were exposed to higher concentrations of tetracycline again. After the fourth exposition, the mutants resistant to ciprofloxacin and sparfloxacin were collected. RESULTS The resistant mutants exhibited a marked increase of the MICs to tetracycline and about 60 fold increase to ciprofloxacin and sparfloxacin. The prominent biochemical properties of drug resistant mutants showed no change in comparison with their parent strains. Drug susceptibility tests suggested that the fluoroquinolones resistance might be inheritable. CONCLUSION Fluoroquinolones susceptible strains could acquire non structure related drug resistance in the presence of high concentrations of tetracycline. It indicates that fluoroquinolones may not effect the pathogenic organisms after a failing treatment with other antibiotics.