Potential preventive role of probiotics against Pseudomonas aeruginosa corneal infection

Introduction. The ocular microbiome plays an important role in the maintenance of physiologic homeostasis of ocular surface and in the prevention of ocular diseases. Alterations of the normal microbiome change microbial composition causing an imbalance in favor of pathogenic species. Among these, Pseudomonas aeruginosa represents a common cause of severe corneal ulceration. The development of new antibiotics for ocular diseases is very slow, highlighting the need for alternative non-antibiotic strategies. Among these strategies, the probiotic therapy could help restoring the homeostasis of ocular surface and preventing or reducing adverse ocular outcomes caused by infection. The aim of this study was to assess the preventive role of probiotics against P. aeruginosa infection on human corneal epithelial cells (HCE). Materials and Methods. The HCE were used to assess the extent of protection by probiotics against P. aeruginosa infection. Probiotics: Lactobacillus reuteri DSM20016, Bifidobacterium longum subsp. infantis DSM20088 and Staphylococcus epidermidis DSM1798. Pathogen: P. aeruginosa ATCC 9027. The following assays were performed: cytotoxicity and adhesion to HCE of probiotics after 24 and 48 h of contact. Antagonism, cytotoxicity, anti-inflammatory and antioxidant properties of probiotics against P. aeruginosa infection were evaluated as follow: pretreatment of HCE with each probiotic (5 x 107 UFC/ml) at 1 h and 24 h prior to P. aeruginosa inoculation (5 x 106 UFC/ml) followed by 1 h and 24 h of growth in combination. Results. S. epidermidis significantly increased HCE vitality and demonstrated a greater ability to adhere to them both after 24 h and 48 h of contact than other probiotics. None of the probiotics have been shown to have antagonistic activity against growth and adhesion of P. aeruginosa to HCE. Instead, they have been shown to restore significantly the HCE viability and to promote the anti-inflammatory and antioxidant activity when in combination with the pathogen. MTT assay revealed that the probiotic combination groups significantly increased cell viability compared to P. aeruginosa infection groups particularly when HCE were pretreated with each probiotic for 24 h and exposed to pathogen for the next 24 h. At the same conditions Elisa test showed that the pretreated HCE significantly reduced the levels of TNF-alpha and increased those of IL-10 whereas Griess assay significantly demonstrated reduction of nitrite/nitrate ratio. Discussion and Conclusions. These results show that pretreatment with probiotics has not a direct role player in contrasting growth and adhesion of P. aeruginosa to HCE but, is to be highlighted that it reduces key factors associated with P. aeruginosa infection.