Efficacy of besifloxacin in a rabbit model of methicillin-resistant Staphylococcus aureus keratitis.
OBJECTIVE
The purpose of this study was to determine the effectiveness of topically applied besifloxacin (0.6%), gatifloxacin (0.3%), and moxifloxacin (0.5%) for the late treatment of experimental methicillin-resistant Staphylococcus aureus (MRSA) keratitis.


METHODS
One hundred colony-forming units (CFUs) of bacteria were injected intrastromally into rabbit corneas. Sixteen hours after infection, one topical drop of phosphate-buffered saline, besifloxacin, gatifloxacin, or moxifloxacin was applied to each eye every 15 minutes for 5 doses and then every 30 minutes for 14 doses. Eyes were examined before and after treatment by slit lamp biomicroscopy. Corneas were harvested from treated and untreated rabbits for the quantitation of bacteria. Minimal inhibitory concentrations (MICs) were determined in vitro for each fluoroquinolone.


RESULTS
None of the treatments had an effect on clinical severity (P > 0.05). Although there were no differences in clinical severity between any groups after treatment, the mean log10 CFU of MRSA recovered from besifloxacin-treated corneas (5.111 +/- 0.251) was significantly lower than the CFU recovered from corneas treated with phosphate-buffered saline (7.006 +/- 0.144), gatifloxacin (7.108 +/- 0.346), and moxifloxacin (7.473 +/- 0.144; P < 0.001). CFU recovered from gatifloxacin- and moxifloxacin-treated corneas were not significantly different from phosphate-buffered saline-treated corneas (P = 1.000). The MICs against the MRSA strain were 8 microg/mL for both gatifloxacin and moxifloxacin, whereas the MIC for besifloxacin was 1 microg/mL.


CONCLUSIONS
Besifloxacin had an 8-fold lower MIC for MRSA than gatifloxacin and moxifloxacin and was significantly more effective than gatifloxacin and moxifloxacin in reducing the number of MRSA in the rabbit cornea 16 hours after infection.
Sanders
Melissa E
ME
Department of Microbiology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
Norcross
Erin W
EW
Moore
Quincy C
QC
Shafiee
Afshin
A
Marquart
Mary E
ME
D000287:Administration, Topical; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D001372:Aza Compounds / Q000008:administration & dosage; D001381:Azepines / Q000008:administration & dosage*; D015169:Colony Count, Microbial; D003320:Corneal Ulcer / Q000188:drug therapy* / Q000382:microbiology; D004195:Disease Models, Animal; D015818:Eye Infections, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D005260:Female; D024841:Fluoroquinolones / Q000008:administration & dosage*; D000077734:Gatifloxacin; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D000077266:Moxifloxacin; D009883:Ophthalmic Solutions; D011804:Quinolines / Q000008:administration & dosage; D011817:Rabbits; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D001372:Aza Compounds; D001381:Azepines; D024841:Fluoroquinolones; D009883:Ophthalmic Solutions; D011804:Quinolines; C522124:besifloxacin; D000077734:Gatifloxacin; D000077266:Moxifloxacin