眼部常见致病菌防耐药突变浓度的测定

Mutant prevention concentrations of antibacterial agents to ocular pathogenic bacteria

目的测定抗菌药物对眼部常见致病菌的防耐药突变浓度（MPC）。方法实验研究。采用微量肉汤倍比稀释法测定左旋氧氟沙星（LVF）、氧氟沙星（OFL）、环丙沙星（CIP）、诺氟沙星（NFL）、妥布霉素（TOB）及氯霉素（CHL）对40株眼部分离菌（金黄色葡萄球菌、表皮葡萄球菌、肺炎球菌、铜绿假单胞菌及肺炎克雷伯杆菌各8株）的最低抑菌浓度（MIC）；通过集菌法将细菌浓度提高到1．2×10^10克隆形成单位／ml，接种其于水解酪蛋白胨（MH）肉汤及胰酶大豆（TSA）培养基中，测定致病菌的MPC。采用SPSS11．0软件，计算出MIC范围、MPC范围、90％MIC和90％MPC（即MIC90、MPC90）、选择指数（MPC90／MIC90）及突变选择窗（MSW，即MIC90与MPC90之间的浓度范围）。结果LVF和TOB对金黄色葡萄球菌的MIC90最低（4mg／L），CIP对绿脓杆菌的MIC90最低（0．25mg／L），LVF对其他3种细菌（表皮葡萄球菌、肺炎球菌及肺炎克雷伯杆菌）的MIC90最低（分别为256．00、1．00、0．25mg／L）；LVF对5种细菌的MPC90、MPC90／MIC90及MSW均最小。从整体趋势看出，CHL的MIC90最大，抗菌活性最弱；LVF的抗菌活性强，但对绿脓杆菌以CIP的抗菌活性最强。CHL和TOB的MPC90较大，防细菌突变能力弱于氟喹诺酮类药物；氟喹诺酮类药物中，以LVF的防细菌突变能力最强。结论左氧氟沙星对眼部分离菌既有较强的抗菌活性又有较强的防细菌突变能力。

Objective To establish a method to measure mutant prevention concentration （MPC） in vitro, and to measure MPC of antibacterial agents for ocular bacteria caused keratitis. Methods It was an experimental study. Forty strains of ocular bacteria were separated from cornea in Beijing Institute of Ophthalmology, which included 8 strains of Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Pseudomonas aeruginosa and Klebsiella pneumoniae respectively. The minimal inhibitory concentration （ MIC ） of the levofloxacin （LVF）, ofloxacin （OFL）, ciprofloxacin （CIP）, norfloxacin （NFL）, tobramycin （TOB） and chlormycetin （CHL） were determined by agar dilution method from National Committee of Clinical Laboratory Standard （ NCCLS）. The MPC were measured by accumulate-bacterial methods with bacterial population inoculated more than 1.2 × 10^10 colony forming units per milliliter with Mueller-Hinton broth and tryptic soy agar plate. With the software of SPSS 11.0, the datum such as the range of MIC, MPC, MICgo and MPC90 were calculated, and the selection index （MPCg0/ MICgo ）and mutant selection window （MSW） were obtained. Results The MIC90 of LVF and TOB（4 mg/L） to Staphylococcus aureus strains were the lowest. CIP showed the lowest MICgo （0. 25 mg/L）to Pseudomonas aeruginosa among six kinds of antibacterial agents. The MICgo of LVF to Staphylococcus epidermidis （256 mg/L）, Streptococcus pneumoniae （1 mg/L ） and Klebsiella pneumoniae （0.25 mg/L ） were lower than other antibacterial agents. The MPC90, MSW and the MPCgo/MIC90 of levofloxacin showed lower values compared with other antibacterial medicines. From all the datum, the MIC90 of CHL was the highest and the activity was the weakest. Although the activity of LVF was higher to every kind of bacteria, CIP had the highest activity antibacterial to Pseudomonas aeruginosa. The capacity of CHL and TOB was weaker than Quinolones for restricting resistant mutants on ocular bacteria. LVF had the strongest capacity for restricting resistant mutants among Quinolones. Conclusion LVF has better antibacterial effects and stronger capacity for restricting the selection of resistant mutants on ocular bacteria than other antibacterial agents.