Ruiz Joaquim, Mensa Laura, Pons Maria J, Vila Jordi, Gascon Joaquim
Centre de Recerca en Salut Internacional de Barcelona, Hospital Clinic/IDIBAPS, C/Villarroel 170, 08036 Barcelona, Spain.
J Antimicrob Chemother. 2008 May;61(5):1016-9. doi: 10.1093/jac/dkn078. Epub 2008 Mar 5.
To select rifaximin-resistant mutants of Escherichia coli and to establish the frequency of mutation, cross-resistance with other antimicrobial agents and the stability of the mutants obtained.
Four E. coli isolates [two enteroaggregative E. coli (EAEC) and two enterotoxigenic E. coli (ETEC)] were used to obtain rifaximin-resistant mutants. The frequency of mutation in the presence of rifaximin, rifampicin and ciprofloxacin was established by growth on plates containing serial dilutions of antibiotic above the bacterial MIC. To determine the stability of rifaximin resistance, 28 selected resistant mutants were grown for 20 consecutive cultures on antibiotic-free plates. Every 10 days, the MICs of rifaximin, chloramphenicol, nalidixic acid and ciprofloxacin were established.
The frequency of mutation in the presence of rifaximin ranged between 5.7 x 10(-7) and 1.6 x 10(-6) in the case of the ETEC isolates, and between 2.0 x 10(-8) and 9.3 x 10(-8) in the case of the EAEC isolates; the frequency of mutation in the presence of rifampicin was in the order of 10(-8) and no mutant in the presence of ciprofloxacin was obtained. Twenty-six out of 28 selected mutants exhibited resistance levels around or higher than 256 mg/L. In all cases, the resistance was stable, and no reversion towards the original parental MIC was observed. In no case was the MIC of chloramphenicol, nalidixic acid or ciprofloxacin affected.
Rifaximin has a low level of resistance selection, although it may select stable highly resistant mutants in a single step. Periodical surveillance of the levels of rifaximin resistance is required to detect the possible appearance of rifaximin-resistant clinical isolates. Further studies to characterize in-depth the mechanisms of stable resistance to rifaximin are necessary.
筛选大肠埃希菌对利福昔明的耐药突变株，确定突变频率、与其他抗菌药物的交叉耐药性以及所获突变株的稳定性。
使用4株大肠埃希菌分离株[2株肠聚集性大肠埃希菌（EAEC）和2株产肠毒素大肠埃希菌（ETEC）]获取对利福昔明的耐药突变株。通过在含高于细菌最低抑菌浓度（MIC）系列稀释抗生素的平板上生长来确定在利福昔明、利福平及环丙沙星存在时的突变频率。为确定利福昔明耐药性的稳定性，将28株筛选出的耐药突变株在无抗生素平板上连续传代培养20次。每10天测定利福昔明、氯霉素、萘啶酸及环丙沙星的MIC。
ETEC分离株在利福昔明存在时的突变频率在5.7×10⁻⁷至1.6×10⁻⁶之间，EAEC分离株在利福昔明存在时的突变频率在2.0×10⁻⁸至9.3×10⁻⁸之间；在利福平存在时的突变频率约为10⁻⁸，在环丙沙星存在时未获得突变株。28株筛选出的突变株中有26株的耐药水平达到或高于256mg/L。在所有情况下，耐药性均稳定，未观察到回复至原始亲本MIC的情况。氯霉素、萘啶酸或环丙沙星的MIC在任何情况下均未受影响。
利福昔明的耐药性选择水平较低，尽管它可能一步筛选出稳定的高耐药突变株。需要定期监测利福昔明耐药水平，以检测可能出现的利福昔明耐药临床分离株。有必要进一步深入研究利福昔明稳定耐药机制的特征。
