Ocular Microbiology and Immunology Group
Back to OMIG Main Page

< Previous | 2021 Agenda and Abstracts | Next >

2021 OMIG Abstract

Enterotoxins Promote Staphylococcus aureus Virulence in Corneal Infections

Rachel Wozniak and William Johnson
University of Rochester Medical Center, Department of Ophthalmology, Rochester, New York

Purpose: Staphylococcus aureus is a major cause of bacterial corneal infections (keratitis). The pathophysiology of this organism in ocular tissues is complex, particularly as S. aureus harbors a diverse array of virulence factors. To further our understanding of S. aureus virulence in keratitis, we sought to explore the role of Staphylococcal Enterotoxins in mediating this blinding disease.

Methods: Clinical keratitis S. aureus isolates either expressing (or devoid of) enterotoxins were first evaluated for adherence, invasion and cytotoxicity using an in vitro corneal epithelial cell model. Corneal epithelial cells were exposed to either bacterial cells or their growth media supernatant for 15, 30, 60 or 90 min. Adherence and invasion were assessed using a gentamicin exclusion assay, while cytotoxicity was measured using the vital dye, trypan blue, to measure cell death in a corneal cell monolayer. S. aureus isolates were then evaluated in an in vivo model of keratitis. Disease severity and bacterial burden were measured at 48h post infection with either Enterotoxin (+) or (-) S. aureus isolates. The host immune response was also determined using ELISAs for IL-6, IL-12, IL-13, TNF-α, and TGF-β on whole murine eye homogenates.

Results: Both strain sets (Enterotoxin (+) and (-)) demonstrated equivalent capacity for corneal cell adherence and invasion. However, starting at 30 minutes, growth media collected from enterotoxin (+) isolates as well as the direct application of bacterial cells resulted in significantly increased corneal cell cytotoxicity. By 90 minutes, Enterotoxin (+) strains resulted in 50% corneal cell death compared to 13% cell death in corneal cells exposed to Enterotoxin (-) strains (p=2.6e-7). In an in vivo model, infection with an Enterotoxin (+) strain resulted in higher bacterial burden compared to an Enterotoxin (-) strain. Of note, the immune response was also significantly altered in mice exposed to an Enterotoxin (+) strain, with decreased levels of IL-6, IL-12, IL-13 and TNF--α noted at 48h post-infection.

Conclusions: Enterotoxins, well known for their role in toxic shock syndrome and food poisoning, have not been previously shown to have a role in mediating keratitis. Our data suggests that these secreted toxins can directly lead to corneal epithelial cell death and may alter the host immune response in order to promote bacterial survival.

Disclosure: N

Support: 2020 Research to Prevent Blindness Career Development Award, K08 EYE29012, Clinician-Scientist Career Development Award

< Previous | 2021 Agenda and Abstracts | Next >