Purpose: To investigate the in vitro susceptibility of Gram-positive and Gram-negative endophthalmitis bacterial isolates to vancomycin, amikacin, and ceftazidime over a 23-year period.
Design: Retrospective non-comparative laboratory case series.
Subjects: Endophthalmitis patients that were culture positive for bacteria.
Methods: Laboratory records of bacteria isolated from endophthalmitis specimens collected from January 1st 1993 to December 31st 2015 were reviewed for incidence and standard susceptibility testing.
Main outcome measures: The in vitro susceptibilities of bacteria cultured from endophthalmitis to vancomycin (VAN), amikacin (AMK), and ceftazidime (CEF).
Results: Patients with endophthalmitis were culture positive for bacteria in 665 cases.. Coagulase negative Staphylococci (CoNS) were the most common bacteria (54.6%), followed by Streptococci (Strep) species (20.8%), Staphylococcus aureus (SA) (10.2%), other Gram-positive (other-GP) bacteria (7.4%) and Gram-negative (GN) bacteria (7.1%). All Gram-positive organisms were susceptible to VAN, with the exception of 2 isolates. The in vitro susceptibilities of bacteria to AMK were: CoNS (95.3%), SA (75.0%), Strep (8.0%), GN (95.7%), and other-GP (81.1%). The in vitro susceptibilities of bacteria to CEF were: CoNS (58.5%), SA (54.4%), Strep (84.1%), GN (93.6.%), and other-GP (52.8%). There was no difference between AMK (95.7%) and CEF (93.6%) for GN coverage. AMK provided better coverage than CEF for CoNS, SA, and other-GP bacteria respectively (p<0.05, Fisher's exact), however, CEF appeared to provide better coverage (p<0.001, Fisher's exact) for Strep than AMK.
Conclusions: Based on standard in vitro susceptibility testing, vancomycin remains an optimal antibiotic choice for the treatment of Gram-positive endophthalmitis. AMK and CEF appear to provide equal GN coverage, but AMK appears to provide better coverage for CoNS, SA, and other-GP, but not Strep.