(771c) Mechanism Study of Selective Killing of Cationic Peptidopolysaccharide Nanoparticles with in vitro and in vivo Efficacy Against Multi-Drug Resistant Bacteria

Antimicrobial peptides (AMPs) are active against many multi-drug resistant (MDR) bacteria but only a limited number of these compounds are in clinical use due to their unselective toxicity. Herein, we show that short peptidopolysaccharide, specifically chitosan-graft-oligolysine (hereafter denoted as CSM5-K5) with molecular weight of about 1450 Daltons, suppresses the growth of methicillin-resistant Staphylococcus aureus (MRSA) bacteria by 3.5 orders of magnitude in a murine wound model, an efficacy comparable to that of the last resort MRSA antibiotic vancomycin; it is also non-inflammatory with little/no activation of neutrophils. In vitro studies show that the polymer is also bactericidal against oxacillin-resistant Staphylococcus aureus (ORSA) and pathogenic strains of Gram-negative Escherichia coli and Pseudomonas aeruginosa and has good fibroblast biocompatibility and hemocompatibility. Light scattering and TEM show that CSM5-K5 aggregate into nanoparticles. Computer simulation shows that hydrogen bonding between chitosan backbones led to nanoparticle formation. However, the other constituent of the copolymer - the oligolysine side chains - interacts with the head groups (PO₄^-) of bacterial membrane through electrostatic interaction. The aggregation of multiple polymers into a single nanoparticle, rather than individual molecules, accentuates the bacterial membrane damage by synergistic clustering of anionic lipids from the zwitterionic lipids. The small nanoparticle size with small cationic charge (zeta potential of + 15 mV) and without hydrophobic residues seems evasive to fibroblasts. This work validates a critical link between the design of a new class of selective antimicrobial nanoparticles formed from short cationic peptidopolysaccharides and its efficacy towards treating MDR infections.