Abstract
Purpose :
To determine if there is a core ocular surface microbiome and whether this changes over time in a healthy cohort using standard microbiological culturing and culture-independent 16S rRNA gene sequencing.
Methods :
Swabs were taken of the superior and inferior bulbar conjunctiva of 45 healthy, non-contact lens wearing participants at three time-points (baseline, 1-month and 3-months) along with 11 negative controls (blank swabs and nuclease free water). Swabs were taken from both eyes of each participant and then randomly assigned to be processed for either microbial culturing using standard biochemical tests or DNA extraction and paired-end 16S rRNA amplicon sequencing using the Illumina MiSeq platform.
Results :
Both cultured cell counts and DNA extract concentrations revealed extremely low microbial biomass on the healthy ocular surface. In total, 75% of samples were culture positive with the most commonly isolated species being coagulase-negative Staphylococcus (CNS) (38% of participants), Proprionibacteria sp (28%), Micrococcus sp. (20%) and Corynebacteria sp. (5%). No species was found in all participants at all times or in all participants in any one time. CNS, Proprionibacteria and Micrococcus were present in at least one or more participants at all times. After quality filtering of 16S rRNA sequencing data and removal of contaminant taxa identified in negative controls, there were 242 operational taxonomic units (OTUs) observed, with the most commonly detected genera Corynebacterium, Acinetobacter, Neisseriaceae and Streptococcus. No OTU was found in all participants at all times or in all participants in any one time but there were 26 OTUs present in at least one or more participants at all times. This included Corynebacterium, Acinetobacter, Neisseriaceae.
Conclusions :
The healthy ocular surface contains very few microbes. Using culture dependent and independent methods, there did not appear to be a core ocular surface microbiome and this was because there was large variation among individuals. However, consistently present taxa could be observed within individuals suggesting the possibility of specific core microbiome rather than a general one. Lastly, contaminant DNA remains the principal challenge in sampling the ocular surface and must not be overlooked.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.