Tear film Microbiota in Meibomian gland dysfunction: Compositional changes and their correlation with meibum lipids and tear film parameters.

Meibomian gland dysfunction (MGD) is the leading cause of evaporative dry eye disease. The multifactorial pathogenesis of MGD remains poorly understood, with limited understanding of the interplay between the microbiome and meibum lipid composition. This study investigates the ocular microbiota and lipid profiles in patients with MGD (n = 20, diagnosed according to TFOS DEWS III criteria) and in Healthy Controls (HC, n = 24). Bacterial isolates from the tear film wash, cultured on blood agar, were assessed for their ability to form biofilms. Meibum collected from the upper and lower eyelids of the same patients was profiled for lipidomics (LC-MS/MS). Bacteria were identified through 16S rRNA gene sequencing and BLAST search analysis. MGD samples showed an increased abundance of Gram-negative bacteria and a significant reduction in the Genus Bacillus. Biofilm-forming capacity was markedly higher in MGD isolates. MGD meibum revealed increased levels of phospholipids and cholesteryl esters. Lipid pathway enrichment analysis (LIPEA) of the differentially abundant lipids linked them to glycerophospholipid metabolism, ferroptosis, autophagy, inflammation, and apoptosis. Spearman correlation analysis between MGD and HC revealed positive correlations between the abundance of biofilm formers and the percentage of polar lipids, total bacterial counts and reduced lipid layer thickness, suggesting their potential interactions in MGD. The results of the study indicate that MGD is characterized by an altered ocular surface microbial composition, increased biofilm-forming capability, and disrupted lipid composition.