Synergistic effect of carboxypterin and methylene blue applied to antimicrobial photodynamic therapy against mature biofilm of Klebsiella pneumoniae

TOSATO, MAIRA GASPAR; SCHILARDI, PATRICIA; LORENZO DE MELE, MÓNICA FERNÁNDEZ; THOMAS, ANDRÉS H.; LORENTE, CAROLINA; MIÑÁN, ALEJANDRO

Heliyon

Cell Press

Año: 2020 vol. 6

2405-8440

The control of multidrug-resistant (MDR) bacteria is a growing public health problem, and new strategies areurgently needed for the control of the infections caused by these microorganisms. Notoriously, some MDR microorganisms generate complex structures or biofilms, which adhere to surfaces and confer extraordinary resistance properties that are fundamental challenges to control infections. One of the promising strategies for thecontrol of MDR bacteria is antimicrobial photodynamic therapy (aPDT), which takes advantage of suitablephotosensitizers (PS), oxygen and radiation to eradicate microorganisms by the generation of highly reactivespecies, including reactive oxygen species (ROS) that cause cytotoxic damage and cell death. Habitual aPDTtreatments use only methylene blue (MB), but MDR microorganism eradication is not completely achieved. Thekey result of this study revealed that a combination of two known PSs, 6-carboxypterin (Cap, 100 μM) and MB(2.5?10 μM) exposed to ultraviolet and visible radiation, presents a synergistic effect on the eradication of a MDRKlebsiella pneumoniae strain. Similar effect was observed when the treatment was performed either with planktonic or biofilm growing cells. Moreover, it was found that after treatment the killing action continues in theabsence of irradiation leading to the eradication of the microorganisms growing in biofilm. Therefore, thecombined aPDT represents a promising strategy for the management of clinical contact surfaces, disinfection ofsurgical instruments, biofouling and even antimicrobial wastewater treatment.