Analysis of Infectious Keratitis Isolates and Antimicrobial Resistance: An 8-Year Retrospective Study in Southern China

Objectives: To characterise the bacterial and fungal spectrum of infectious keratitis (IK) in southern China and to evaluate changes in the bacterial profiles and antimicrobial resistance (AMR) over an 8-year period (2017–2024). Methods: This retrospective study included patients with culture-positive IK treated between 2017 and 2024. Corneal scrapings were obtained for microbiological culture and pathogen identification. Antimicrobial susceptibility testing was performed for all bacterial isolates. Microbial distribution and in vitro antibiotic susceptibility were analysed. Results: A total of 2785 microbial isolates were recovered from 2741 patients. Overall, fungal isolates predominated (59.6%), exhibiting a distinct seasonal distribution, with Fusarium (40.2%) and Aspergillus (14.3%) being the most common genera. Among bacterial isolates, Gram-positive organisms were predominant (63.6%). The most frequently identified Gram-positive organisms were coagulase-negative staphylococci (CNS; 34.9%), while Pseudomonas (18.9%) was the most common Gram-negative pathogen. Over the study period, an increase in the proportions of CNS (p < 0.001) and Serratia was observed (p = 0.017), alongside a decline in Pseudomonas (p = 0.009) and Kocuria (p < 0.001). Resistance among Gram-positive isolates increased for penicillin (from 62.3% to 74.4%; p = 0.002) and levofloxacin (from 26.4% to 46.9%; p < 0.001), whereas Gram-negative resistance generally declined. Conclusions: IK in southern China is characterised by persistent fungal predominance and evolving bacterial composition. AMR patterns differ between Gram-positive and Gram-negative organisms, reflecting both shifts in pathogen distribution and species-specific resistance changes, highlighting the importance of continued regional surveillance to guide empirical therapy.