Photodynamic enhancement of the activity of antibiotics used in urinary tract infections

Photodynamic therapy (PDT) has been proven to kill different microbial cells. However, to our knowledge, none of the available reports describes the modulatory effect of this therapy on the antibacterial activity of antibiotics against Escherichia coli rods being the main causative agent of urinary tract infections (UTIs). Therefore, the aim of our study was to verify if the PDT can enhance the antibacterial activity of antibiotics recommended in the treatment of UTIs. An attempt to determine the optimal conditions of PDT to enhance the bactericidal activity of ciprofloxacin, amikacin, and colistin has been made. In order to find the optimal antimicrobial conditions, the efficacy of four protocols associated with the use of different energy doses (70 and 120 J/cm2) and chlorin e6 (Ce6) concentrations (50 and 100 μg/mL) has been verified. The antibacterial effect of combined PDT and antibiotics was assessed by the time-kill assay. The best results were achieved for Ce6 at a concentration of 100 μg/mL and the energy dose 120 J/cm2 for bacterial suspensions treated with ciprofloxacin. Taken together, our results showed that PDT using Ce6 improves the antibacterial activity of antibiotics effectively inhibiting bacterial growth and being promising in the elimination of bacterial UTIs in humans.