Pathogen Spectrum and Antimicrobial Susceptibility Profiles in Culture-Proven Endophthalmitis at a Tertiary Referral Center in China: A Three-Decade Retrospective Study

Background/Objectives: Endophthalmitis is a devastating, vision-threatening intraocular infectious disease. Given the scarcity of long-term cohort data in Asian populations, appropriate empirical antibiotic therapy is essential to prevent irreversible vision loss. The present study aimed to identify the culture-positive pathogen profiles and antimicrobial susceptibility in endophthalmitis. Methods: This retrospective study included 90 culture-positive isolates from patients with endophthalmitis treated between January 1990 and October 2020. The etiology, clinical presentation, and antibiotic susceptibility profiles of the isolates were analyzed. Results: Forty-three isolates were Gram-positive cocci, 23 were Gram-negative bacilli, and 24 were fungi. Postoperative infections were dominated by Gram-positive cocci (72.1%). Furthermore, 47.8% (11/23) of Gram-negative bacilli and 66.7% (16/24) of fungi were recovered from endogenous endophthalmitis isolates. In patients with endophthalmitis caused by Gram-negative bacilli, visual acuity was numerically inferior at both initial presentation and final follow-up visit (p = 0.051 and p = 0.018). All isolates of Gram-positive cocci exhibited full susceptibility to vancomycin and teicoplanin, while linezolid yielded a susceptibility rate of 96.9% (31/32). For Gram-negative bacilli, over 80% of isolates were susceptible to amikacin, aztreonam, and third-generation cephalosporins, whereas carbapenems and fluoroquinolones achieved susceptibility rates exceeding 90%. Among staphylococcal isolates, ciprofloxacin resistance was significantly higher in patients older than 55 years compared with those aged 55 years or younger (71.4% versus 12.5%; exact p = 0.013). Conclusions: Postoperative infection was the leading cause of Gram-positive cocci endophthalmitis. Antimicrobial susceptibility profiles validated intravitreal vancomycin combined with ceftazidime as a rational regimen for empirical antibacterial coverage. Elevated fluoroquinolone resistance among Gram-positive cocci, particularly in elderly patients, underscores the necessity of sustained regional antimicrobial resistance surveillance and periodic reassessment of conventional topical antibiotic prophylatic protocols.