Antimicrobial photoinactivation approach based on Safranine-O loaded F127 copolymeric micelles for control of gram-negative and gram-positive bacteria

Abstract

The present study aims to evaluate the photodynamic efficiency of Safranine-O (Sf) in the inactivation of Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923). Sf cytotoxicity activities were evaluated against L929 fibroblasts, J774A.1 macrophages, and LLCMK2 cells (monkey [Macaca mulatta] kidney epithelial cells) by tetrazolium salt assays (MTT). Photodynamic therapy (PDT) is a therapeutic modality that has shown effectiveness in the inactivation of microorganisms. Sf-mediated photodynamic inactivation of microorganisms (PDIM) was performed at different concentrations of the photosensitizer (PS) with a minimum inhibitory concentration (MIC) of 9.4 μg mL−1 for the two bacteria evaluated and a minimum bactericidal concentration (MBC) of 9.4 μg mL−1 for E. coli and 37.5 μg mL−1 for S. aureus. The bacteria viability was analyzed by flow cytometry through staining with propidium iodide (PI). The population of 10,000 bacteria (E. coli or S. aureus) treated with PDIM showed cell mortality of 21.5% and 30.48%, respectively. The morphological analysis of the pathogens allowed the investigation of cell damage involved with PDIM by scanning electron microscopy (SEM) and transmission (MET). Sf-mediated PDT proved to be efficient with severe photodamage and effective inactivation of Gram negative and Gram-positive bacteria.