Changes in Staphylococcus aureus Virulence Factors and Host Immune Response Following Rose Bengal Photodynamic Antimicrobial Therapy

Abstract

Purpose : Staphylococcus aureus (S. aureus) virulence factors as well as the host inflammatory response makes management challenging. Optimal therapy would neutralize the S. aureus toxins while reducing the host immune response. One such therapy under investigation is Photodynamic Antimicrobial Therapy (PDAT). The impact of PDAT on the S. aureus virulence factors and the host immune response remains unknown. The purpose of this study is to measure the changes in: (1) virulence factors of two S. aureus isolates and (2) the subsequent immune response in an ex-vivo EpiCorneal tissue model following rose bengal PDAT.

Methods : (1) Virulence Factors: One methicillin-resistant S. aureus (MRSA) and one methicillin-susceptible S. aureus (MSSA) isolate were collected from patients with infectious keratitis. The inocula (10⁵ CFU/mL) were mixed with either water or 0.1% rose bengal, and plated in triplicate onto blood agar. Plates with rose bengal were irradiated with a custom-made green LED light source. Organisms were collected from each plate, DNA was extracted, and virulence factors were quantified by metagenomics (CosmosID). (2) Host Immune Response: Evaluated using EpiCorneal tissue model (MatTek). Control, Infection, and Infection-PDAT groups were tested in duplicate. Infection and Infection-PDAT groups were inoculated using the same S. aureus isolates described above. In the Infection-PDAT group, 0.1% rose bengal was applied and irradiated as described above. Fluids from the groups were collected and IL-1β, -6 and -8 quantified with ELISA.

Results : The frequency of the 35 virulence factors varied among the MRSA (12/35) and MSSA (21/35) strains. The subgroup of virulence factors relating to leukocyte migration and phagocytosis (SSL-5, -7,-10,-11, CHIPS, SOX) were more expressed in MSSA compared to MRSA, except SSL-11, and all were downregulated following rose bengal PDAT. Furthermore, the host immune response was higher in the S. aureus Infection groups compared to Control group. IL-8 showed the greatest response, followed by IL-6 and IL-1β. In the Infection-PDAT group, the largest downregulation of immune factors was observed in the MSSA strain.

Conclusions : This study demonstrates that virulence factors of S. aureus isolates and the subsequent immune response in EpiCorneal tissue models vary among S. aureus strains and are altered following rose bengal PDAT.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.