Purpose: To study the microbial spectrum and antibacterial susceptibility of vitreous cultures in a tertiary referral center in Northeast United States.
Methods: All vitreous samples sent to the microbiology laboratory at a tertiary referral center from January 1988 to December 2008 were included in the study. The distribution and antibiotic susceptibility of all isolates from culture-positive samples were compared across 3 equal time periods 1988-1994, 1995-2001, and 2002-2008.
Results: One hundred forty-three positive cultures, where 11.9% (n=17) were polymicrobial, yielded a total of 160 isolates that consisted of 80.6% (n=129) gram-positive isolates, 12.5% (n=20) gram-negative isolates, and 6.9% (n=11) fungal isolates. The most prevalent organisms were coagulase-negative Staphylococcus (CoNS) (37.5%, n=60), Viridans Streptococcus (11.3%, n=18), and Streptococcus pneumoniae (6.9%, n=11). Other common gram-positive isolates include Propionibacterium acnes (5.6%, n=9), other Streptococcus species (4.4%, n=7), Staphylococcus aureus (4.4%, n=7), and Enterococcus faecalis (3.8%, n=6). The most common gram-negative isolates were Klebsiella species (3.1%, n=5), Moraxella species (3.1%, n=5), and Haemophilus species (2.5%, n=4). Vancomycin was effective against all CoNS, Sta. aureus, Viridans Streptococcus, and E. faecalis tested, and all Sta. aureus isolates were oxacillin sensitive. Of all CoNS isolates, 83.3% during 1988-1994, 73.1% during 1995-2001, and 100% during 2002-2008 were resistant to at least 1 of the antibiotics tested in the study with the last time period showing an increase in resistance (P=0.021, adjusted standard residual=2.0). CoNS showed a decreasing resistance over time to chloramphenicol and gentamicin (P=0.010, P=0.007, respectively) and an increase in resistance to penicillin and tetracycline during 2002-2008 (P=0.003, P=0.040, respectively). Susceptibility to other antibiotics did not show significant dependence on time.
Conclusion: Bacteria causing endophthalmitis showed variable resistance to antibiotics over time. The importance of adequately treating endophthalmitis in the setting of these resistance pattern changes stresses the importance of periodic evaluation of causative organisms to ensure appropriate empiric treatment.