Inativação fotodinâmica de Enterococcus spp. por porfirinas catiônicas

Abstract

Introduction: Enterococcus are common human and animal’s intestinal commensals and can cause opportunistic infections. Reports of healthcare-associated infections (HAIs) caused by this bacterial genus have increased in recent years. Biofilm formation is the most important virulence factor in the establishment of these infections. Furthermore, strains obtained from both humans and animals are generally multidrug-resistant, which are associated with limited therapeutic options. Therefore, using photosensitizers, such as porphyrin, has gained importance as an alternative in controlling resistant strains. Objective: To evaluate the antimicrobial and antibiofilm activity of cationic porphyrins after photoactivation on Enterococcus spp. Material and methods: The porphyrins 3-H2TMeP+ and 4-H2TMeP+ were used, as well as 25 Enterococcus strains, including three references and 22 clinical isolates from humans (from dental canals) and animals (dog, cat, goat and snake). The species studied included E. faecalis, E. faecium, E. casseliflavus, E. gallinarum, and E. hirae. The MIC100 and MBC100 were determined by broth microdilution tests, following the CLSI M07-A9 (2012) standard. Assays with reactive oxygen species (ROS) scavengers were also performed to identify which ROS are involved in photoinactivation, and atomic force microscopy (AFM) was used to assess cellular changes after treatment with the photoactivated porphyrin. Results: The results indicated that antimicrobial photodynamic therapy (aPDT) with the tested cationic porphyrins was effective, , exerting a bactericidal effect at micro-concentrations (0.27 to 8.75 µM) against Enterococcus spp. strains tested. Both porphyrins showed antibiofilm activity under light, with greater activity at concentrations up to 4.38 µM. Data suggests the activity of type I and II oxidative pathways in E. faecalis and E. faecium. AFM analysis revealed a significant reduction in adhesion energy and changes in mechanical stiffness, accompanied by topographic disorganization and heterogeneity on the bacterial surface. Conclusion: Antimicrobial photodynamic therapy using cationic porphyrins showed promising results in inactivating of Enterococcus spp., leading to changes in surfaces’ adhesion, which tends to reduce colonization and biofilm formation. Thus, this suggests that aPDT may be a possible alternative in fighting against microbial resistance, especially in infections associated with biofilms.