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.
Fungal keratitis can lead to pain and impaired vision. Current treatment options include antifungal agents and therapeutic penetrating keratoplasty. An emerging option for the management of keratitis is photodynamic antimicrobial therapy (PDAT) which uses a photosensitizer rose bengal activated with green light. Utilizing a pulsed irradiation, rather than the standard continuous irradiation may have a similar antimicrobial effect with less total energy. This study is to compare pulsed and continuous rose bengal mediated PDAT for inhibition of six fungal isolates on agar plates: Fusarium solani, Fusarium keratoplasticum, Aspergillus fumigatus, Candida albicans, Paecilomyces variotti, and Pseudoallescheria boydii. Isolates were mixed with 0.1% rose bengal and exposed to three irradiation conditions: (1) 30-minute continuous (10.8J/cm2), (2) 15-minute continuous (5.4J/cm2), (3) 30-minute pulsed (5.4J/cm2). Plates were photographed at 72 hours and analyzed with custom software. At 72 hours, 30-minute continuous rose bengal mediated PDAT inhibited all six fungal species. Fungal inhibition was analogous between 30-minute continuous and 30-minute pulsed test groups, with the exception of A. fumigatus. The 15-minute continuous irradiation was less effective when compared to both 30-minute continuous and 30-minute pulsed groups. These in vitro results demonstrate the potential strength of pulsed rose bengal mediated PDAT as an adjunct treatment modality for fungal keratitis.
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