Exploring the potential for microbial transfer from exhaled breath to the ocular surface: a comparative analysis of...

Respiratory microbes typically enter the body via the nose and mouth, but transmission through the ocular surface-nasolacrimal duct route remains poorly understood. This study investigated the microbiota of exhaled breath, conjunctiva, and anterior nares in healthy individuals to assess the potential for microbial transfer from exhalations to the ocular surface.

Cross-sectional, single-center observational study.

Exhalation, conjunctival, and nasal samples were collected from 20 participants. Exhaled breath samples were obtained by having participants read a standardized script for three minutes in front of a sterile agar plate positioned 15 cm from the mouth. Sterile phosphate-buffered saline was applied to the agar surface and a sterile cell scraper was used to collect the sample. Conjunctival and nasal samples were collected using sterile flocked swabs. All samples were stored at - 80 °C. Microbial DNA was extracted, followed by PCR amplification and paired-end 16S rRNA gene sequencing on the Illumina MiSeq platform.

The cohort included 20 participants (8 female, 12 male; mean age 41.9 ± 9.2 years). Significant differences were found in microbial richness (P < 0.0001), evenness (P < 0.01), and bacterial community structure (P < 0.001) across sites. While 9 % of amplicon sequencing variants (ASVs) were shared across all sites, only 1 % were shared between exhalations and the conjunctiva. The anterior nares shared more ASVs with both the conjunctiva (8 %) and exhalations (20 %).

Minimal microbial overlap between exhaled breath and the conjunctiva suggests that in healthy adults, under specific low-intensity conditions tested, direct transmission to the ocular surface appears minimal.