AIM: To investigate and analyze the changes in the conjunctival flora of patients exposed to repeated antibiotic usage. In addition, determining the effects of this repeated exposure on the resistance pattern of the conjunctival flora.

METHODS: This study included 40 patients, admitted to the Retina Unit of the Research Institute of Ophthalmology. All chosen patients had a minimum of 4 consecutive, monthly intravitreal injections(IVI), some were extended to 6mo or 1y as required. The patients were randomly divided into 3 groups and each group received one kind of antibiotic which was either ofloxacin, moxifloxacin or ceftazidime. All bacterial isolates were tested for antibiotic susceptibility using Kirby-Bauer disc diffusion technique.

RESULTS: In this study the conjunctival normal flora at baseline culture varied from a predominance of Staphylococcus epidermidis (51.2%), followed by Staphylococcus aureus 14% to Micrococcus species 12.8% and other coagulase negative staphylococci(CONS)13%. Our results showed an increase in the percentage of Staphylococcus epidermidis among ceftazidime treated eyes during the four visits in comparison to baseline cultures of patients randomized to ceftazidime. In contrast, there was no noticeable increase in Staphylococcus aureus percentage from baseline. In fluoroquinolone treated eyes, we also observed an increase in percentage of Staphylococcus epidermidis from base line. In contrast to ceftazidime treated eyes, the Staphylococcus aureus percentage in fluoroquinolone treated eyes showed an increase from baseline. However, the pattern of the ocular flora composition changed with the exposure to the old and newer generation of fluoroquinolones. We noticed an increase of Staphylococcus epidermidis in moxifloxacin treated eyes than that in ofloxacin treated eyes from baseline. There was no observed difference in the pattern of Staphylococcus aureus regarding exposure to older and newer generations of fluoroquinolones.

CONCLUSION: Repeated use of ophthalmic antibiotics not only alters the composition of the normal ocular flora, but also selects for resistant strains.