Peptídeos antimicrobianos sintéticos contra Enterococcus resistente à vancomicina

Abstract

Bacteria of the genus Enterococcus are among the main causes of healthcareassociated

infections (HAIs) and exhibit a broad spectrum of antibiotic resistance, with vancomycin-resistant Enterococcus (VRE) being one of the most significant. Antimicrobial peptides (AMPs) are molecules that are part of the innate immune system, present in all living beings, capable of participating in the defense against microbial infections. Synthetic antimicrobial peptides (AMPs) emerge as a promising option to overcome antimicrobial resistance. This study aimed to evaluate the antibacterial and antibiofilm effects of eight AMPs against vancomycin-resistant E. faecalis and E. faecium, as well as to investigate their mechanisms of action and activity in combination with conventional antibiotics. Eight synthetic AMPs, named Mo-CBP 3 -PepI, Mo-CBP 3 -PepII, Mo-CBP -PepIII, RcAlb-PepI, RcAlb-PepII, RcAlbPepIII,

PepGAT, and PepKAA, were tested for their in vitro antibacterial activity against E. faecalis ATCC ® 3 51299, E. faecium NCTC ® 12202, and four clinical VRE isolates (Etf1, Etf4, Etf5, and Etf7). The results showed that, individually, the AMPs demonstrated 20–48% inhibition of E. faecalis ATCC ® 51299 growth, with the highest value achieved by Mo-CBP -PepI. However, when combined with the antibiotic chloramphenicol, which alone showed 36% inhibition, the activity increased to 55– 76%. The highest inhibitory activity was observed with the combination of chloramphenicol with RcAlb-PepIII (76%) and PepKAA (70%), representing a 2- to 3fold

increase compared to the compounds used alone. Microscopic analyses demonstrated that the treatment of E. faecalis ATCC 3 ® 51299 cells with the combination of AMPs and chloramphenicol caused significant damage to the bacterial membrane. Regarding the biofilm of E. faecalis ATCC 51299, the maximum inhibition achieved with AMPs alone was 22% (Mo-CBP -PepII), ranging from 10–33% when combined with chloramphenicol. In tests with VRE isolates of E. faecium, the maximum inhibition was 58%, achieved with Mo-CBP 3 3 -PepII against the Etf5 isolate. This isolate, which showed the highest resistance to vancomycin (maximum of 35% growth inhibition), was also the most susceptible to combined treatment with AMPs and vancomycin. The combination of vancomycin with MoCBP -PepI reached 64% inhibition, a 2- to 5-fold increase compared to vancomycin alone. For E. faecium, the maximum biofilm inhibition was 33%, while biofilm degradation reached 46% with the AMPs used alone. These findings suggest that the evaluated peptides have potential as candidates for the development of new drugs against enterococcal infections caused by resistant strains, either as standalone treatments or in combination with existing antibiotics.