Endophthalmitis caused by gram-negative bacteria: etiologies, antibiotic susceptibilities, and treatment outcomes

BACKGROUND: To report the etiologies, antibiotic susceptibilities, and treatment outcomes of patients with culture-proven endophthalmitis associated with gram-negative organisms. METHODS: A single-center retrospective chart review of patients with positive vitreous cultures for gram-negative organisms who presented to a referral center from January 2014 to May 2025. RESULTS: The study included 46 patients (mean age 69.5 years; 58.7% male). The most common isolates were Pseudomonas aeruginosa (19/46, 41.3%), Haemophilus influenzae (8/46, 17.4%), Klebsiella pneumoniae (3/46, 6.5%), Morganella morganii (3/46, 6.5% and Serratia marcescens (3/46, 6.5%). The most common etiologies were post-operative (20/46, 43.5%), followed by bleb-associated (9/46, 19.6%), corneal ulcer (6/46, 13.0%), trauma (5/46, 10.9%), endogenous (4/46, 8.7%), and suture-related (2/46, 4.3%). Most tested organisms were susceptible to amikacin (32/34, 94.1%), gentamicin (33/36, 91.7%), ceftazidime (36/37, 97.3%), tobramycin (33/35, 94.3%), and ciprofloxacin (34/37, 91.9%). Lower susceptibility rates were observed for trimethoprim-sulfamethoxazole (12/18, 66.7%) and ceftriaxone (13/15, 86.7%). All tested organisms were susceptible to meropenem (30/30, 100%). At the last follow-up, only 13.0% (6/46) of patients had a visual acuity of 20/800 or better, and 30.4% (14/46) of patients had no light perception. Enucleation or evisceration was performed in 28.3% of patients (13/46). CONCLUSION: In the current study, there were generally favorable susceptibilities to commonly used intravitreal antibiotics, but overall patients had poor visual outcomes regardless of specific causative organisms and etiologies. Despite appropriate treatment with intravitreal antibiotics and/or pars plana vitrectomy, enucleation and evisceration were common.