Pasquali Frédérique, Manfreda Gerardo
Department of Food Science, Alma Mater Studiorum, University of Bologna, Fanin 44, 40127 Bologna, Italy.
Vet Microbiol. 2007 Jan 31;119(2-4):304-10. doi: 10.1016/j.vetmic.2006.08.018. Epub 2006 Aug 17.
The mutant prevention concentration (MPC) is a new concept meant to face the increased prevalence of antibiotic resistance by using antibiotic concentrations able to prevent the selection of single-step resistant mutants. In the present study, the MPCs of ciprofloxacin and enrofloxacin were evaluated against fully susceptible strains of Escherichia coli, Salmonella Typhimurium and Pseudomonas aeruginosa. Additionally, representative single-step mutants arising after exposure to sub-MPC antibiotic concentrations were investigated for molecular basis of their fluoroquinolone resistance phenotypes. MPC value was recorded when more than 10(10) CFU/mL were spread on Muëller Hinton Agar supplemented with different antibiotic concentrations (from 1X to 16X MIC value). MICs of original strains as well as single-step mutants were determined in presence or absence of the Efflux Pump Inhibitor Phe-Arg-beta-naphthylamide (PAbetaN). Moreover point mutations in the QRDR of the gyrA and parC genes were investigated by sequencing. The enrofloxacin MPC values were 4-16-fold higher than ciprofloxacin values. E. coli and S. Typhimurium representative single-step mutants showed reduced susceptibilities associated with point mutations in the QRDR of the gyrA gene or efflux pump system. P. aeruginosa mutants showed resistance phenotypes associated predominantly with efflux pump system activity. According to in vitro MPC data, ciprofloxacin showed a better efficacy than enrofloxacin, in preventing the selection of E. coli, S. Typhimurium and P. aeruginosa single-step mutants. However, in relation to AUC/MPC ratio, the MPC concept can be applied in vivo to ciprofloxacin and enrofloxacin for E. coli and S. Typhimurium but not for P. aeruginosa.
突变预防浓度（MPC）是一个新概念，旨在通过使用能够防止单步耐药突变体产生的抗生素浓度来应对日益普遍的抗生素耐药性问题。在本研究中，评估了环丙沙星和恩诺沙星对大肠杆菌、鼠伤寒沙门氏菌和铜绿假单胞菌完全敏感菌株的MPC。此外，还研究了暴露于低于MPC的抗生素浓度后出现的代表性单步突变体对氟喹诺酮耐药表型的分子基础。当在补充了不同抗生素浓度（从1倍到16倍MIC值）的穆勒-欣顿琼脂上涂布超过10(10) CFU/mL时记录MPC值。在有或没有外排泵抑制剂苯丙氨酸-精氨酸-β-萘酰胺（PAbetaN）的情况下测定原始菌株以及单步突变体的MIC。此外，通过测序研究gyrA和parC基因喹诺酮耐药决定区（QRDR）中的点突变。恩诺沙星的MPC值比环丙沙星的值高4至16倍。大肠杆菌和鼠伤寒沙门氏菌的代表性单步突变体显示出与gyrA基因QRDR中的点突变或外排泵系统相关的敏感性降低。铜绿假单胞菌突变体显示出主要与外排泵系统活性相关的耐药表型。根据体外MPC数据，在防止大肠杆菌、鼠伤寒沙门氏菌和铜绿假单胞菌单步突变体产生方面，环丙沙星显示出比恩诺沙星更好的疗效。然而，就AUC/MPC比值而言，MPC概念可在体内应用于针对大肠杆菌和鼠伤寒沙门氏菌的环丙沙星和恩诺沙星，但不适用于铜绿假单胞菌。
