Chitosan nanoparticles enhance the efficiency of methylene blue-mediated antimicrobial photodynamic inactivation of bacterial biofilms: An in vitro study

Abstract Background Biodegradable chitosan nanoparticles (CSNPs) with an intrinsic antimicrobial activity may be a good choice to improve the effectiveness of antimicrobial photodynamic inactivation (APDI). The aim of this study was to investigate the effect of CSNPs on the efficiency of methylene blue (MB)-mediated APDI of Staphylococcus aureus and Pseudomonas aeruginosa biofilms. We also assessed the phototoxicity of MB + CSNPs towards human fibroblasts. Methods CSNPs were prepared using ionic gelation method and characterized by dynamic light scattering (DLS) and field-emission scanning electron microscope (FESEM). Biofilms were developed in a 96-well polystyrene plate for 24 h. In vitro phototoxic effect of MB + CSNPs (at final concentrations of 50 μM MB) at fluence of 22.93 J/cm 2 ) on biofilms were studied. Appropriate controls were included. Also, in vitro cytotoxicity and phototoxicity of the above mixture was assessed on human dermal fibroblasts. Results DLS and FESEM measurements confirmed the nanometric size of the prepared CSNPs. APDI mediated by the mixture of MB and CSNPs showed significant anti-biofilm photoinactivation (P  3 and >2 log 10 CFU reduction in S. aureus and P. aeruginosa biofilms, respectively) while MB-induced APDI led to approximately 10 CFU reduction. At the same experimental conditions, only 25.1% of the fibroblasts were photoinactivated by MB + CSNPs. Conclusion Our findings showed that CSNPs enhanced the efficacy of MB-APDI; it may be due to the disruption of biofilm structure by polycationic CSNPs and subsequently deeper and higher penetration of MB into the biofilms.