In Vitro Inactivation of Antibiotic Resistant Bacteria Using Antibacterial Photodynamic Therapy (aPDT)

Abstract

Antimicrobial resistance (AMR) is considered the scourge of this era, and the mortalities associated with infectious diseases induce by multi-drug resistant (MbR) pathogens are high. Keeping AMR in mind, researchers are developing novel antimicrobial photodynamic therapy (aPDT), which has been demonstrated to be efficient against microbes that exhibit resistance to a variety of antimicrobial drugs. This study's objective was to assess methylene blue (MB)-based aPDT's effectiveness in conjugation with a 635nm diode laser (red light), to inactivate MDR- pathogenic Pseudomonas aeruginosa and Staphylococcus aureus. These MDR strains were exposed to all concentrations of methylene blue without being exposed to light (+MB -L), after that treated with a 635nm diode laser without methylene blue (-MB +L), and then exposed to methylene blue (MB) (15 .625, 31.25, 62.5, 125, 250, and 500~Lg/ml) all concentrations in combination with (18.00, 36.00, 54.00, 72.00, 90.00, 108.00 J/cm2) 635nm diode laser of 300mW/cm2 (+MB +L) in sterilized condition (Biosafety cabinet) for 60, 120, 180,240, 300, and 360 seconds. The inhibition of bacteria was demonstrated by CFU/ml, optical density (OD 600nm), fluorescence spectroscopy, and confocal microscopy (LSM). After irradiation, both bacterial strains were significantly reduced except for MB and diode laser alone. In P. aeruginosa, a 39.86% to 100% reduction was reported, and in S. aureus, a 49.22% to 100% reduction was reported. The most bactericidal effect was reported at 500, 250, and 125 ~g/ml for 180, 240, 300, and 360 seconds of exposure with 54.00, 72.00, 90.00, and 108.00 J/cm2 of laser dose at 300 W/cm2 . Antimicrobial photodynamic therapy using methylene blue and 635nm diode laser broadly ,killed the MDR strains of both grams (positive and negative) bacteria at an equal level (310g and 610g reduction). aPDT could be a promising alternative to conventional antimicrobial therapy, to cope with resistant pathogens in treating bacterial infections.