JAN 13, 2011
Increasing resistance of normal ocular flora to commonly used antibiotic classes, including macrolides, aminoglycosides, and third-generation fluoroquinolones, has led to the widespread use of more potent fourth-generation fluoroquinolones. However, resistance to these fourth-generation fluoroquinolones has also emerged. There is concern that repeated exposure of ocular and nasopharyngeal flora to topical antibiotics after intravitreal injections may result in resistant strains.
To evaluate the resistance patterns of ocular and nasopharyngeal flora exposed to repeated short-term applications of topical antibiotics over time, the authors of this study collected cultures from the conjunctiva of 24 patients undergoing intravitreal injections for choroidal neovascularization to determine their baseline resistance to 16 different antibiotics.
The most common organisms were coagulase-negative staphylococci (CNS), representing 37 (65 percent) of the 57 isolated strains. The most common CNS organisms were Staphylococcus epidermidis and Staphylococcus lugdunensis, accounting for 73 percent and 11 percent of CNS isolates, respectively. Of the CNS isolates, 60 percent were resistant to three or more antibiotics and 30 percent were resistant to five or more antibiotics. More than 50 percent of isolates demonstrated some level of resistance to ofloxacin and levofloxacin, and 33 and 37 percent showed some level of resistance against gatifloxacin and moxifloxacin, respectively.
These results suggest an increasing trend of multiresistant ocular flora. Combined with the results of other studies, they also suggest that multiresistance may be associated with greater virulence and increased infection rates. Greater understanding of antibiotic susceptibility patterns of ocular flora in this patient cohort may have important implications for the prevention and treatment of postinjection endophthalmitis.