J. Hopf, J. Olesk, C. Evans, J. Ross, D. Donahue, V. Ploplis, F. Castellino, S. Lee, P.D. Nallathamby
University of Notre Dame,
Keywords: AMR, biomimic, antibiotic resistance, broad spectrum, threat agnostic, agent agnostic, phage-mimicking
Summary:We are losing in an antibiotic arms race with bacteria due to the emergence and global spread of new antibiotic resistance mechanisms. At current antibiotics discovery and development rates, we will eventually lose to antibiotic-resistant strains. By 2050, antibiotics-resistant strains of bacteria will kill more patients per year than all cancers combined. Therefore, there is a desperate need to look for methods beyond antibiotics to kill harmful bacteria and slow the rise of drug-resistant bacterial pathogens. This work describes an antibiotic-independent, structure-based antimicrobial nanoparticle system that is effective for topical applications (e.g., wound infections), while effectively disrupting the bacterial populations in wounds and on implant materials that are responsible for recurrent infections. The nanoparticles can also be administered intra-venously. We investigated a new class of core-shell (SiO2@Au@Ag) nanoparticles with a silica core, a discontinuous shell of silver-alloyed gold nanospheres, and with or without rationally designed antimicrobial peptides (PhANPs, pep1@PhANPs). The spacing of the silver-alloyed gold nanospheres was designed to mimic the spacing of spikes on bacteriophages such as PRD1. The antimicrobial peptides are a library of rationally designed peptides from the amino acid sequences of streptolysins. The nanoparticles were effective in the solution phase or the immobilized phase. Seven bacterial species which were multi-drug resistant were chosen as test organisms: Staphylococcus aureus USA300, Pseudomonas aeruginosa FRD1, Enterococcus faecalis, Corynebacterium striatum, Klebsiella pneumoniae, Acinetobacter baumannii (BAA1605) and Streptococcus pyogenes. Dose-dependent bacterial growth curves were measured on plate readers. Bacterial viability was assessed using CFU assays and fluorescent LIVE/DEAD assays. Biocompatibility of PhANPs and pep1@PhANPs to human cells (HaCaT) was evaluated using ethidium homodimer permeabilization assay. Pep1@PhANPs immobilized on implant-grade steel coupons achieved a 100% kill rate of bacteria that encountered the implant surface. PhANPs and pep1@PhANPswere completely biocompatible with model skin cells (HaCaT keratinocytes), thus confirming their suitability for topological applications. The phage- mimicking peptide-free PhANPs killed ~65% of all bacterial species. The anti-microbial peptide 1 immobilized on the antibiotic-free, phage-mimicking nanoparticles (pep1@PhANPs) demonstrated a > 99%bacterial kill rate against all infectious bacterial strains at a peptide concentration on pep1@PhANPs that was ~10X lower than the concentration of free peptides required to achieve similar results. Interestingly, the pep1@PhANPs and PhANPs showed a silver dose-dependent antibacterial effect as well. We had also demonstrated the in vivo biocompatibility of the PhANPs in mice through bio-clearance studies and a lack of inflammation in organs when a pathologist scored histology sections. We successfully mimicked the nanoarchitecture of antimicrobial viruses (Phages) and demonstrated a nanostructure-dependent antimicrobial effect that will be a viable alternative to traditional antibiotics. The 100%bacterial killing rate achieved by liquid dispersed pep1@ PhANPS or surface-immobilized pep1@PhANPs and polymer@PhANPs is a good indicator for their application as antimicrobial formulations or antimicrobial coatings on implant surfaces. Ongoing research has validated these results in in vivo rat and mice wound infection models in clearing the wound infections and promoting wound healing.