Distinct Ocular Surface Microbial Profiles in Corneal Transplant Candidates

Purpose: To characterize the ocular surface microbiome in patients undergoing corneal transplantation and to evaluate microbial shifts associated with corneal endothelial decompensation and surgical history. Methods: In this single-center case-control study, conjunctival swabs were collected from 54 adults scheduled for lamellar or penetrating keratoplasty and from 16 healthy controls. Sampling was performed under sterile conditions immediately before surgery. Bacterial DNA was analyzed by 16S rRNA gene sequencing targeting the V3-V4 regions. Alpha and beta diversity indices were calculated using the Shannon index and Bray-Curtis dissimilarity. Taxonomic composition was compared across groups stratified by clinical status and prior ocular surgery. Results: Pretransplant patients showed significantly higher alpha diversity than healthy controls (P = 0.04), and beta diversity analysis confirmed distinct microbial community structures between groups (P = 0.002). The patient group exhibited enrichment of Enterobacteriaceae, Pseudomonas, and Escherichia-Shigella, whereas Bacteroidota and Bacteroidia predominated in healthy subjects. No significant differences in diversity or composition were observed between decompensated and nondecompensated cases. Patients with prior penetrating keratoplasty displayed higher microbial diversity than those with previous phacoemulsification (P = 0.03). Conclusions: Corneal transplant candidates exhibit distinct ocular surface microbial profiles characterized by increased diversity and enrichment of opportunistic taxa. Although endothelial decompensation did not significantly alter microbial composition, prior surgical history appeared to influence diversity patterns. These exploratory findings provide preliminary evidence that the ocular surface microbiome may play a role in the preoperative assessment and postoperative outcomes of corneal transplantation.