Comprehensive Analysis of the Conjunctival Sac Microbiome in Patients With Evaporative Dry Eye and Mixed Dry Eye.

Purpose: This study aimed to investigate the differences in the microbial community of the conjunctival sac (CS) between patients with evaporative dry eye (EDE) and patients with mixed dry eye (DE), then, to compare it with previously reported ocular surface microbial of healthy people. Methods: CS swabs were collected from 10 patients with EDE and 10 patients with mixed DE. Bacterial DNA from these swabs were analyzed using 16S ribosomal RNA (rRNA) gene amplicon sequencing. Alpha diversity analysis assessed the microbial community diversity, while beta diversity was evaluated. Bioinformatic analysis of relative abundances and the functional annotations were performed at the genus level. Results: Results indicated no significant difference in alpha diversity, but a significant difference in beta diversity was observed (P = 0.001). Notably, Ralstonia and Corynebacterium exhibited significant differences. At the species level, the colonization rates and abundances of bacteria, including Comamonas denitrificans, Raoultella planticola (R. planticola), Pseudomonas mosselii, and Pseudomonas aeruginosa were significantly different. Functional annotation revealed that disparities in the microbial composition from CS between the two groups were accompanied by differences in the expression levels of genes involved in carbohydrate metabolism and histidine kinases, which were elevated in the mixed DE group. Conclusions: The microbial community structure of the EDE group was comparable to that of the mixed DE group. However, notable differences were observed in the relative abundance and colonization rate of certain specific microorganisms. These variations were associated with alterations in carbohydrate metabolism and histidine kinase expression. Translational Relevance: Corynebacterium, and Ralstonia may play important roles in the pathogenesis of dry eye disease (DED).