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

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 mu M 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 < 0.001, >3 and >2 log(10) CFU reduction in S. aureus and P. aeruginosa biofilms, respectively) while MB-induced APDI led to approximately <1 log(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. (C) 2016 Elsevier B.V. All rights reserved.