Control of mucoid Pseudomonas aeruginosa biofilms in a highly porous skin model (ex vivo/in vitro model) with carbosilane dendrimer-endolysin complexes

Abstract

The alarming rise in antibiotic resistance in Pseudomonas aeruginosa, resulting from its ability to undergo enzymatic modifications, mutate, or form complex structures such as biofilms, has rendered many conventional therapies ineffective, creating an urgent need to search for new antimicrobial agents. Ligand-modified nanoparticles are a promising alternative to conventional agents. For example, silver-containing dendrimers (metallodendrimers), which permeabilize the bacterial outer membrane, enhance the production of reactive oxygen species, and, in combination with peptidoglycan-degrading proteins—CHAP-domain endolysins—can cross the barrier of Gram-negative bacteria. However, their activity against mature biofilms and potential cytotoxicity to mammalian tissues remain poorly understood. In this study, we used an ex vivo pig ear skin model to evaluate the ability of three carbosilane dendrimers and their combinations with endolysin to inhibit biofilm formation with P. aeruginosa PAO1. The irregular skin texture and richer nutrient resources in the ex vivo model may limit the effectiveness of nanomaterials compared to the biophilic P. aeruginosa in the in vitro model on a smooth plastic surface. Early application of dendrimers with endolysin significantly reduces bacterial survival, while late application causes excessive damage to the epidermis, making it difficult for dendrimers to reach the bacteria and hindering the assessment of the effectiveness of antibacterial drugs. These results clearly suggest that studies on the antibacterial activity of various nanomaterials on smooth surfaces differ significantly from the highly porous structure of the skin model, which has an important impact on their limited application in the treatment of skin wounds.