Shifting trends in in vitro antibiotic susceptibilities for common bacterial conjunctival isolates in the last decade at the New York Eye and Ear Infirmary

Background Bacterial conjunctivitis is one of the most common forms of ocular diseases worldwide. The purpose of this study is to determine the most common pathogens causing bacterial conjunctivitis, their in vitro susceptibility to existing antibiotics, and the changing trends in bacterial resistance to antibiotics over the last decade. Methods Records of all conjunctival bacterial cultures performed at the NYEEI Microbiology Laboratory from 1 January 1997 through 30 June 2008 were reviewed. Data on species of bacterial isolates and their in vitro susceptibility to the antibiotics tetracycline, trimethaprim/sulfamethoxazole (TMP/ SMZ), imipenem, fluoroquinolones (ciprofloxacin, moxifloxacin, gatifloxacin), aminoglycosides (gentamicin, tobramycin), erythromycin, cefazolin, oxacillin, and vancomycin were collected. Results Review of records yielded 20,180 conjunctival bacterial cultures, 60.1% of which were culture-positive. Of the culture-positive isolates, 76.6% were gram-positive and 23.4% were gram-negative pathogens. Staphylococcus aureus was the most common gram-positive pathogen isolated, and also the most commonly isolated pathogen overall. Haemophilus influenzae was the most common gram-negative pathogen. A significant increase in the percentage of methicillin-resistant Staphylococcus aureus (MRSA) was observed in the course of 11.5 years. The highest levels of antibiotic resistance were observed to tetracycline, erythromycin, and TMP/SMZ. Grampositive isolates were least resistant to vancomycin, and gramnegative isolates were least resistant to imipenem. The lowest broad-spectrum antibiotic resistance was observed in the case of moxifloxacin, gatifloxacin, and aminoglycosides. Conclusion Staphylococcus aureus is the most common pathogen in bacterial conjunctivitis. Conjunctival bacterial isolates demonstrated high levels of resistance to tetracycline, erythromycin and TMP/SMZ. Moxifloxacin and gatifloxacin appear to be currently the best choice for empirical broad-spectrum coverage. Vancomycin is the best antibiotic for MRSA coverage.