Changes in ocular flora in eyes exposed to ophthalmic antibiotics.

To determine changes in ocular flora in individuals repeatedly exposed to topical macrolide or fluoroquinolone antibiotics. Prospective, controlled, longitudinal study with 1-year follow-up. Forty-eight eyes of 24 patients undergoing serial unilateral intravitreal injection for choroidal neovascularization. Patients received 4 consecutive monthly unilateral intravitreal injections and were then treated as needed. Each patient was randomized to 1 of 4 antibiotics (azithromycin 1%, gatifloxacin 0.3%, moxifloxacin 0.5%, ofloxacin 0.3%) and used only their assigned antibiotic for 4 days after each injection. Conjunctival cultures of the treated eye and untreated fellow eye (control) were taken at baseline and before each injection. All bacterial isolates were tested for antibiotic susceptibility to 16 different antibiotics using the Kirby-Bauer disc diffusion technique. Changes in bacteria composition of the conjunctiva over time. In azithromycin-treated eyes, Staphylococcus epidermidis and Staphylococcus aureus accounted for 54.5% and 18.2% of cultured isolates, respectively, at baseline and 90.9% (P<0.01) and 4.5% (P<0.01), respectively, after azithromycin exposure. In fluoroquinolone-treated eyes, 45.7% and 6.5% of cultured isolates at baseline were S epidermidis and S aureus, respectively, but these percentages increased to 63.4% (P<0.03) and 13% (P = 0.24), respectively, after fluoroquinolone exposure. In contrast, the percentage of gram-negative species decreased from 8.7% at baseline to 1.6% (P<0.05) in fluoroquinolone-treated eyes. The percentage of S epidermidis isolated from azithromycin-treated eyes was significantly greater when compared with fellow control eyes (P<0.01) or fluoroquinolone-treated eyes (P<0.01). The percentage of S epidermidis isolated from the conjunctival surface significantly increases after repeated exposure to azithromycin and to a lesser degree fluoroquinolone antibiotics at the expense of other commensal flora. The author(s) have no proprietary or commercial interest in any materials discussed in this article.