The ocular surface is constantly exposed to the dangers of the environment, including pathogenic bacteria. Bacterial infections of the human eye by gram positive bacteria can cause severe visual impairments. S. aureus is a major ocular pathogen as it possesses potent virulence factors in its armamentarium: fibronectin-binding protein A (FnbpA) and Fnbp B, fibrinogen binding proteins (ClfA and ClfB), iron regulated surface determinant A (IsdA), wall teichoic acid (WTA), b-defensins 2 and 3, cathelicidin, RNase 7, cytokines, chemokines, adhesion molecules, and granulopoiesis factors, alpha-toxin, phenol soluble modulins (PSM), and Panton-Valentine leukocidin (PVL), protein A (SpA), Exfoliative toxins (ETA and ETB) and toxic shock syndrome toxin (TSST), LukAB (LukGH) and PSMs, staphylocoagulase. S. pneumoniae in eye infections is most involved in keratitis, conjunctivitis, and endophthalmitis. The microorganism firstly colonizes the nasopharynx via the neuraminidases NanA, NanB, and NanC. Then, acts through hyaluronate lyase, pneumococcal capsule, autolysin, pneumolysin, zinc metalloproteinases. Streptococcus pyogenes is most involved in blepharitis and hospital acquired conjunctivitis. Its virulence factors include: cysteine proteinase, streptococcal pyrogenic erythrogenic toxin B, streptokinase, cell envelope protease, Streptococcus secreted esterase, streptolysin O and streptolysin S, M protein, endo-β-N-acetylglucosaminidase. E. faecalis is implicated in postoperative endophthalmitis cases. These strains produce a cytolysin with a large lytic subunit (CylLL) and a small lytic subunit (CylLS) and are related with poor visual outcome. Bacillus cereus can cause a rapidly destructive endophthalmitis via its peptidoglycan, flagella, hemolysins, lipases, enterotoxins, proteases, cereolysin AB, cereolysin O, and collagenase. Corynebacterium (non-diphtheriae) species: They possess pili with tissue tropism to colonize host tissues. After initial attachment additional minor pilins help anchoring, and provide proximity between the bacterial surface and the host cell plasma membrane. The arsenal of gram positive microorganisms that can cause ocular infections and the understanding of their mechanisms of action can elucidate further therapeutic targets and promote rapid treatment.

Panagiota Xaplanteri has graduated from Medical School, Patras University in 1999 and acquired the medical specialty of Biopathology (Laboratory Medicine) in 2007. She has completed her PhD in 2008 from Medical School, Patras University, Greece and her MSc in Health Care Management, Hellenic Open University in 2018. She has worked in the following positions: Senior Assistant, Department of Microbiology, University General Hospital of Patras, Greece, 2015-today, Part time Assistant Professor, School of Rehabilitation Sciences, University of Patras, Greece, 2019-today, Part time Lecturer/Assistant Professor, School of Sciences of Health and Care, Technological Educational Institute of Western Greece, Patras, 2007-2019. She has published more than 20 papers.