Endolysin CHAP domain-carbosilane metallodendrimer complexes with triple action on Gram-negative bacteria: Membrane destabilization, reactive oxygen species production and peptidoglycan degradation

Bacterial resistance to antibiotics is a significant challenge that is associated with increased morbidity and mortality. Gram-negative bacteria are particularly problematic due to an outer membrane (OM). Current alternatives to antibiotics include antimicrobial peptides or proteins and multifunctional systems such as dendrimers. Antimicrobial proteins such as lysins can degrade the bacterial cell wall, whereas dendrimers can permeabilize the OM, enhancing the activity of endolysins against gram-negative bacteria. In this study, we present a three-stage action of endolysin combined with two different carbosilane (CBS) silver metallodendrimers, in which the periphery is modified with N-heterocyclic carbene (NHC) ligands coordinating a silver atom. The different NHC ligands contained hydrophobic methyl or N-donor pyridyl moieties. The effects of these endolysin/dendrimer combinations are based on OM permeabilization, peptidoglycan degradation, and reactive oxygen species production. The results showed that CBS possess a permeabilization effect (first action), significantly reduced bacterial growth at higher concentrations alone and in the presence of endolysin, increased ROS production (second action), and led to bacterial cell damage (third action). The complex formed between the CHAP domain of endolysin and a CBS silver metallodendrimer, with a triple mechanism of action, may represent an excellent alternative to other antimicrobials with only one resistance mechanism.