Influence of coagulase-negative staphylococci as potential probiotics on Dry Eye

Introduction. Dry eye (DE) is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort, visual disturbance and tear film instability with potential damages to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface. Among the factors that cause DE, the most common is the dysfunction of the Meibomian glands that contribute to the production of the lipid component of the film. This condition alters the integrity of the ocular surface and, consequently, the microbiome. The altered microbiome exerts its pathogenetic effect in favor of a proliferation of bacteria that can produce lipase, potentiating inflammation, and triggering the innate immune response. Coagulase-negative staphylococci (CoNS) are the most frequently identified species in a healthy eye. However, Pseudomonas, Acinetobacter, Bacillus and Corynebacterium are the most frequently isolated genera in patients with DE. The objective of the study was to assess the properties of a probiotic strain of Staphylococcus epidermidis as a prototype for a screening study aimed at evaluating the probiotic capabilities of CoNS isolated from patients with DE. Materials and Methods. Strains: S. epidermidis DSM1798, Lactobacillus reuteri DSM20016, Bifidobacterium longum DSM20088, S. aureus ATCC 6538 and Pseudomonas aeruginosa ATCC 9027. In vitro, probiotic abilities have been evaluated by the following tests: aggregation, co-aggregation to pathogenic strains, biofilm production, lipase production, cytotoxicity and adhesion to corneal epithelial cells (HCE). Results. S. epidermidis and B. longum have been shown to have significant self-aggregating and co-aggregating capabilities versus P. aeruginosa, as well as ability to produce biofilms at 24 h (p  0.05 %). L. reuteri showed both significant co-aggregating capacity vs S. aureus and ability to produce biofilm at 48 h. The three probiotic strains produced no lipase and showed no cytotoxicity. S. epidermidis showed a significant ability to adhere to HCE after 24 h and 48 h of incubation. B. longum showed the same capacity after 48h. Discussion and conclusions. Restoring the ocular microbiota could improve the prognosis of the ocular surface involved in diseases such as DE. S. epidermidis probiotic has been shown not to produce lipase, to produce biofilms, to have good aggregating and self-aggregating capabilities, excellent ability to adhere to HCE and not to be cytotoxic. The results obtained with this probiotic strain encourage the continuation of the study towards the identification of CoNS isolated from patients with or without DE with probiotic abilities more specific to the ocular surface.