Changes in drug susceptibility and the quinolone-resistance determining region of Staphylococcus epidermidis after administration of fluoroquinolones.

摘要

PURPOSE: To evaluate the correlation between changes in the susceptibility of bacteria and mutations in the quinolone-resistance determining region (QRDR) after 3 weeks of continuous fluoroquinolone instillation. SETTING: Miyata Eye Hospital, Miyazaki, Japan. METHODS: In this prospective randomized study, gatifloxacin 0.3% eyedrops or levofloxacin 0.5% eyedrops were administered for 1 week before cataract surgery and for 2 weeks after surgery. Samples were collected from the conjunctival sac before instillation of the antibiotic agent and 14 days after surgery. Susceptibility to the fluoroquinolones and gene mutations in the QRDR of the isolated Staphylococcus epidermidis were analyzed. RESULTS: The detection rate of S. epidermidis was 27% in the gatifloxacin group (n=79 eyes) and 21% in the levofloxacin group (n=73 eyes) before instillation of the antibiotic and 6% and 19%, respectively, 14 days postoperatively. The susceptibility rates of S. epidermidis strains to levofloxacin were statistically significantly lower after instillation than before antibiotic instillation, and the number of gene mutations in the QRDR was statistically significantly higher after instillation. There was no difference in the gatifloxacin group between before and after antibiotic instillation. In the 9 eyes in which S. epidermidis was detected in samples taken before and after antibiotic instillation, most strains were genetically different from each other between the 2 time points. CONCLUSIONS: Three-week continuous instillation of levofloxacin affected the indigenous bacterial flora in the conjunctival sac, suggesting possible induction of microbial substitution to fluoroquinolone-resistant S. epidermidis. However, there was no change with gatifloxacin.