Understanding the microbial requirements for colonization and immunogenicity of commensal bacteria at the ocular surface

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Abstract Ocular surface disease has an astounding economic burden of over $12 billion per year for treatment. While current standards of care only treat symptoms rather than address the cause(s) of disease, recent data suggest that manipulation of the microbiome may be a potential avenue to treat and/or prevent disease. Recently, an ocular commensal bacterium, Corynebacterium mastitidis (C. mast), was identified and shown to protect the ocular surface from infection with C. albicans and P. aeruginosa. Despite this beneficial immunity, there is still a need to understand the microbial factors that govern ocular colonization and ability to stimulate the host immune response. The foundation of the proposed studies was built upon preliminary data acquired from genomically and phenotypically screening over 30 clinically relevant isolates of Corynebacterium spp. and nearly 2000 transposon mutants of C. mast. Specifically, the first aim will identify microbial factor(s) that govern ocular colonization by testing eight C. mast mutants that were predicted to lack an ability to colonize the eye. The second aim will discover microbial factor(s) that stimulate host immunity by assessing immunogenicity, in vitro and in vivo, of nine different C. mast mutants that were predicted to have a limited ability to induce immune responses. The third aim will mechanistically define how ocular commensal bacteria stimulate the human immune response. As outlined, the proposed studies will provide multiple layers of information beneficial to ocular health. First, Aims 1 and 2 will provide the identity of specific genes that play a critical role in the nature of an ocular commensal, which will allow future studies to better distinguish true ocular commensals from other bacteria that are temporarily introduced to the eye. These aims will also shed light on genes that may be desirable in the formulation of genetically modified ocular bacteria or ocular probiotics. Finally, Aim 3 will provide valuable knowledge on a virtually unknown area, which is the human immune response against Corynebacterium spp. Because Corynebacteria are fairly ubiquitous throughout the body, these data will have far-reaching implications for not only the eye, but throughout the rest of the body. In sum, the proposed studies will form the foundation for the future development of ocular probiotics to treat eye diseases.