Synergistic effect of Carboxipterin and Methylene blue applied to antimicrobial photodynamic therapy against mature biofilm of Klebsiella pneumoniae

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

Viña del Mar

Congreso; XIV ELAFOT; 2019

ELAFOT

Multidrugresistance (MDR) bacteria is a serious and frequent health problem that resultsin the failure of infections treatment. Currently, new strategies for thecontrol of the infections caused by these microorganisms are urgently needed.Notoriously, some MDR microorganisms generate complex structures or biofilms,which adhere to surfaces and confer extraordinary resistance properties thatare fundamental challenges to control infections. One of the promisingstrategies for the control of MDR bacteria is antimicrobial photodynamictherapy that is a minimally invasive technique based on a photochemical processin which a non-toxic photosensitizer (PS) can be activated by low doses ofradiation of a specific wavelength [1][2]. The absorbed energy generates radicals on biomolecules and highlyreactive oxygen species (ROS), including superoxide anion (O2?-)and hydroxyl radicals (OH?) (Type I reactions) or singlet oxygen (1O2,type II reactions) that cause cytotoxic damage and cell death [3]. The selection of PSs is the key point to get successful results inthe aPDT treatment. Habitual PDI treatments use only methylene blue (MB,3,7-bis (dimethylamino)-phenothiazin-5-ium chloride) that under radiation itshows bactericidal effects against both Gram-positive and Gram-negativebacteria, but MDR microorganism eradication is not completely achieved. Inparticular, Klebsiella pneumoniae isan opportunistic Gram negative pathogen, responsible of several diseases, suchas urinary tract infections, pneumonia, septicemias, and soft tissue infections[4]. Some K. pneumoniaestrains are extremely resistant to antibiotic treatments due to their capacityto generate biofilms. The key result of this study revealed that a combinationof two known PSs, 6-carboxypterin (Cap, 100 µM) and methylene blue (MB, 2.5-10µM) exposed to ultraviolet and visible radiation, presents a synergistic effecton the eradication of a MDR Klebsiellapneumoniae strain. Similar effect was observed when the treatment wasperformed either with planktonic or biofilm growing cells. Moreover, it wasfound that after treatment the killing action continues in the absence ofirradiation leading to the eradication of the microorganisms growing inbiofilm.