Introduction: In the past 25 years, methicillin-resistant Staphylococcus aureus (MRSA) strains have grown in both magnitude and diversity, making it more difficult for healthcare providers to treat these types of infections. Virulence factors of MRSA allow it to adapt to its environment and develop antibiotic resistance rapidly. One alternative treatment to combat these resistant pathogens is PDAT. Previous studies demonstrated the inhibitory effect of PDAT against MRSA isolates; however, there is limited knowledge regarding the effect of PDAT on virulence factors (toxins, defense mechanisms, stress response).
Purpose: To evaluate the impact of rose bengal (RB) and riboflavin (RI) PDAT on the virulence factors of six different ocular species of MRSA.
Methods: Suspensions were made with six separate MRSA species inocula (108CFU/mL) with either water (control), 0.1% RB, or 0.1% RI solutions. Each suspension was aliquoted onto an agar plate and exposed to either dark or a 5.4J/cm2 irradiation dose with custom-made LED irradiation sources [λ= 525nm (RB) or 375nm (RI)]. Plates were incubated for 48 hours and then photographed for percent growth measurement. Microbial samples were collected from each plate from which DNA was extracted and sent for full genome sequencing at CosmosID.
Results: Rose bengal PDAT completely inhibited the growth of all six MRSA species within the irradiation zone, while riboflavin had minimal inhibition. The dark conditions for both photosensitizers showed minimal inhibition. Full genome sequencing revealed that the virulence factors had varying responses to PDAT, depending on the MRSA species, photosensitizer used, and light exposure.