Anti-Infective Effects of a Low-Temperature Plasma Source on Human Cornea

Abstract

Purpose: : A prototype of a plasma (ionized gases) source, operating at low power and atmospheric pressure, has been developed to treat corneal infections. We have previously shown that the anti-microbial activity was directly dependent on exposure time and on microbial species. The purpose of the present study was to investigate the effects of the plasma on different pathogens and on human infected and non-infected cornea in vitro.

Methods: : Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans and Herpes Simplex were used as prototype pathogens. The plasma’s effects on pathogens were evaluated by analyzing the colony forming units (CFU) and the formation of atomic and molecular free radicals (ROS). Pseudomonas aeruginosa and Staphylococcus aureus infected human cornea were treated with the plasma source 12 hours after superficial stromal injection of bacterial suspensions. CFU and histological assessments were performed 24 hours after the treatment. The plasma effects on human epithelial cells and fibroblasts were also investigated by FACS analysis.

Results: : After application of plasma for 2 minutes, a significant reduction of bacterial viability was observed in the samples from infected treated cornea compared to non-treated cornea. Treatment of human cornea with plasma did not cause any significant modification of the structure of the whole cornea, stromal collagen and basal membrane associated collagens. The ROS production by pathogens cultures was confirmed within 5 minutes after plasma treatment with different peaks depending on pathogen’s species. Treated cell cultures demonstrated a 30% reduction of viability at 12 hours but a 95% recovery at 24 hours. No effect on herpes simplex reproduction was observed in vitro.

Conclusions: : Cold plasma reduces bacteria viability in human infected cornea. ROS production is involved in the antibacterial activity of the treatment. This plasma source can be considered as a potential new tool in ophthalmologic practice for treating cornel bacterial infections.

Keywords: microbial pathogenesis: experimental studies • antibiotics/antifungals/antiparasitics • cornea: clinical science