Toward the Characterization of the Human Core Ocular Surface Microbiome.

Purpose: The field of ocular surface microbiome (OSM) research suggests its involvement in ocular surface (OS) health and disease. However, existing OSM data are heterogeneous. This study aims to provide a whole-metagenome shotgun sequencing-based description of the healthy core ocular surface microbiome (COSM), encompassing all taxonomic kingdoms at species-level resolution. Methods: Swabs from the conjunctiva and lower lid margin, and tear fluid of 27 individuals without OS disease aged 40 to 60 years were collected at 3 time points. The OSM was sequenced and taxonomically and functionally profiled using Kraken2 and HUMAnN3, respectively. To validate sequencing results, human and microbial proteins of the tear fluid, termed the tear proteome (TP), were characterized by nano liquid chromatography-tandem mass spectrometry (nLC-MS/MS) and profiled by gene ontology. The COSM was defined as the microbiome present in most of the study population over time. Therefore, species present in > 50% of all samples across the three time points were considered to form the COSM. Results: At species level, Cutibacterium acnes, Malassezia restricta, and Staphylococcus epidermidis formed the COSM, with Corynebacterium segmentosum additionally being part of the core lid microbiome (LM). No significant differences in the OSM and human TP were observed between the left and right eyes on individual levels. However, the variance between subjects mostly exceeded that between eyes within subjects, suggesting an individual-specific COSM and TP. Conclusions: The description of the COSM provides the basis for future OSM research and potential targets for preventive and therapeutic interventions of the OS and associated diseases.