Antibiotic susceptibility patterns of ocular bacterial flora in patients undergoing intravitreal injections

To determine the antibiotic susceptibility patterns of conjunctival flora in patients undergoing intravitreal (IVT) injection.

Prospective, observational study.

Patients (n = 85) scheduled to undergo 136 IVT injections at California Vitreoretinal Center at Stanford University.

Conjunctival cultures were obtained on the day of the IVT injection from the injection site bulbar conjunctiva before the application of povidone-iodine or antibiotics.

Bacterial isolates were identified and tested for antibiotic susceptibility using either the Kirby-Bauer disc-diffusion technique or MicroScan-WalkAway system.

Our analysis included 136 samples collected from 90 eyes of 85 patients. Of those with positive cultures (n = 65), the most common bacterial isolates were coagulase-negative staphylococci (CNS), comprising 59 (83%) of the 71 bacterial strains. Among the CNS, all were susceptible to vancomycin and >80% were susceptible to gentamicin, chloramphenicol, tetracycline, and imipenem. Between 60% and 80% of the CNS were susceptible to the cephalosporins and newer generation fluoroquinolones. Fewer than 60% were susceptible to the penicillin analogs, erythromycin, and the earlier generation fluoroquinolones. Nearly half of the CNS (47%) were resistant to oxacillin/methicillin.

Bacteria isolated from the injection site of patients undergoing IVT injections were mostly CNS. Most are sensitive to vancomycin, gentamicin, and chloramphenicol.

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