Toward improving therapeutic regimens for Bacillus endophthalmitis.
OBJECTIVE
Bacillus cereus causes the most virulent and refractory form of endophthalmitis. The authors analyzed the effectiveness of early treatment with vancomycin or gatifloxacin, with or without dexamethasone, for experimental B. cereus endophthalmitis.


METHODS
Rabbit eyes were injected intravitreally with 100 colony-forming units of B. cereus. At 2, 4, or 6 hours after infection, eyes were injected intravitreally with 0.1 mL gatifloxacin (0.3%), vancomycin (1.0%), either antibiotic plus dexamethasone, dexamethasone alone (1.0%), or PBS. Eyes were analyzed by electroretinography, bacterial quantitation, and antibiotic penetration analysis. Drug toxicity toward Müller cells, retinal pigment epithelium, and cones was also analyzed.


RESULTS
Eyes treated at 2 hours with vancomycin or gatifloxacin, with or without dexamethasone, maintained higher ERG amplitudes than the dexamethasone alone and PBS control groups. Eyes treated with antibiotic plus dexamethasone at 6 hours had reduced retinal function compared to antibiotic treatment alone. With the exception of vancomycin with or without dexamethasone at 6 hours, all antibiotic treatments sterilized eyes. Only gatifloxacin reached aqueous concentrations greater than the minimal inhibitory concentration for B. cereus when measured at 8 hours. Neither gatifloxacin nor vancomycin was toxic to retinal cells in vitro.


CONCLUSIONS
Early intravitreal injection of vancomycin or gatifloxacin improved the therapeutic outcome of B. cereus endophthalmitis. The addition of dexamethasone to antibiotic treatment did not provide a therapeutic benefit over antibiotics alone and appeared to reduce the antibiotic efficacy of vancomycin 6 hours after infection. In this model, delay in treatment past 6 hours significantly reduced the potential for salvaging useful vision.
Wiskur
Brandt J
BJ
Oklahoma Center for Neuroscience, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
Robinson
Michael L
ML
Farrand
Allison J
AJ
Novosad
Billy D
BD
Callegan
Michelle C
MC
D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D001409:Bacillus cereus / Q000187:drug effects* / Q000502:physiology; D001682:Biological Availability; D003907:Dexamethasone / Q000627:therapeutic use; D004195:Disease Models, Animal; D004359:Drug Therapy, Combination; D004596:Electroretinography; D009877:Endophthalmitis / Q000188:drug therapy* / Q000382:microbiology; D015818:Eye Infections, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D024841:Fluoroquinolones / Q000627:therapeutic use; D000077734:Gatifloxacin; D005938:Glucocorticoids / Q000627:therapeutic use*; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy* / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D011817:Rabbits; D012160:Retina / Q000502:physiology; D014640:Vancomycin / Q000627:therapeutic use; D014822:Vitreous Body / Q000382:microbiology
D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D005938:Glucocorticoids; D014640:Vancomycin; D003907:Dexamethasone; D000077734:Gatifloxacin