The combination of methylene blue and sodium dodecyl sulfate enhances the antimicrobial photodynamic therapy of Candida albicans at lower light parameters

Abstract

BackgroundThe growth of resistant microorganisms has been a challenge for health systems. Antimicrobial Photodynamic Therapy (aPDT) has gained attention due to its effects on resistant strains. Recently, it was shown that the association of methylene blue (MB) and sodium dodecyl sulfate (SDS) are an effective strategy to increase the effect of aPDT; however, it is unknown which are the best light parameters (such as irradiance and radiant exposure, RE), to reach the most effective protocols. This work aimed to evaluate the light parameters, irradiance, and radiant exposure, in aPDT with MB when conveyed in water compared to MB associated with SDS. MethodsTests were carried out to quantify the colony-forming units (CFU) of ATCC 10,231 strain of Candida albicans when using MB in different media and with different light parameters: Control (water), SDS (0.25%), MB (20 mg/mL), and the MB/SDS at irradiances of 3.7; 11.2; 18.6, and 26.1 mW/cm2 and varied irradiation times to reach radiant exposures of 4.4; 17.8; 26.7, and 44 J/cm². ResultsThe results showed that aPDT with MB/SDS had a higher antimicrobial effect than MB when conveyed in water. Furthermore, for the highest irradiance studied (26.1 mW/cm2), CFU decreases exponentially with increasing RE from 4.4 up to 44 J/cm2. Similarly, at a fixed RE, the higher the irradiance used, the higher the antimicrobial effect was observed, except for the lowest RE studied (4.4 J/cm2). ConclusionsaPDT with MB/SDS had a greater antimicrobial action at the lower light parameters when compared to MB conveyed in water. The authors suggest the use of RE above 18 J/cm2 and irradiance above 26 mW/cm2 since at the mentioned parameters the increase in its value caused a greater antimicrobial effect.