In vitro Susceptibilities to Topical Antibiotics of Bacteria Isolated from the Surface of Clinically Symptomatic Eyes

Background: The permanent change of resistance patterns of bacteria causing ocular infections makes repeat susceptibility testings against the most recent clinical isolates mandatory. The aim of the present study was to assess the in vitro susceptibility of ocular bacterial isolates of clinically symptomatic eyes admitted to the outpatient clinic of the eye department of a large central hospital to commonly used topical antibiotics. Methods: Ocular isolates (n = 454) were tested for their susceptibility to ofloxacin, ciprofloxacin, norfloxacin, gentamicin, tobramycin, meomycin, bacitracin, erythromycin, tetracycline and chloramphenicol. Results: All three tested fluoroquinolones were found to be very effective against gram-negative organisms but demonstrated some weakness against certain strains of gram-positive germs, in particular coagulase-negative staphylococci and Streptococcus viridans. These germs, however, were very susceptible to bacitracin and chloramphenicol. The relative overall in vitro efficacy was (in decreasing order): chloramphenicol, ciprofloxacin, ofloxacin, norfloxacin, bacitracin, tetracycline, neomycin, erythromycin, tobramycin and gentamicin. Conclusion: Chloramphenicol had the highest overall in vitro efficacy, but has potential lethal side effects. The fluoroquinolones were highly effective, especially being superior to the aminoglycosides tested, but no single antibiotic provided 100% coverage against all of the bacterial isolates that were tested.