The role of Staphylococcus aureus alpha-toxin on corneal epithelial wound healing

Abstract

Purpose : Staphylococcus aureus (S aureus) is a common cause of bacterial infections in the cornea. It has also been shown colonization by S aureus leads to delayed and abnormal corneal wound healing. We evaluated the effects of S aureus alpha-toxin (wild type) on corneal epithelial wound healing.

Methods : The effect of live wild type and wild type conditioned media (CM) on corneal epithelial wound healing was tested using the scratch assay on telomerase-immortalized human corneal epithelial cells (HCEC) in vitro and central 2-mm corneal epithelial debridement model in C57bl/6J mice. The invasiveness of the wild type and isogenic hla mutant strains of S. aureus was evaluated in human corneal epithelial cells in vitro and also in a murine keratitis model in vivo study.

Results : Both wild type and wild type CM significantly delayed corneal epithelial wound healing in vitro and in vivo. After 6 hours, wound closure ratio (WCR) was 9 ± 6 percent after incubation with wild type CM compared to 48 ± 9 percent with unconditioned media in vitro (P<0.001). In vivo, WCR after 24 hours was 23 ± 16 percent compared to 80 ± 5 percent, respectively (P<0.001). Heating the CM abrogated its inhibitory effect and increased WCR to 54 ± 5 percent in vitro and 48 ± 8 percent in vivo (P<0.001 compared to wild type CM). Similarly, isogenic hla mutant strains S aureus had significantly less inhibitory effect on wound healing with WCR of 43 ± 10 percent in vitro and 72 ± 8 percent in vivo compared to the wild type (P<0.05). Hla mutant strains S aureus was less able to invade human corneal epithelial cells in vitro with 34250 ± 5737 mean bacterial count inside the cells (BC) compared to 6032 ± 7506 BC with wild type and in vivo, with 84750 ± 16660 BC and 34805 ± 46611 BC, respectively (P<0.001 for all comparisons).

Conclusions : Alpha-toxin plays a major pathogenic role both in the invasiveness of S aureus and its pathologic modulation of corneal epithelial wound healing. Targeting alpha toxin may provide a new therapy to modulate S aureus pathogenesis on the cornea.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.