Light-Activated Silver Nanoparticles to Eliminate Antibiotic Resistant Bacteria and Genes

Abstract
The development of microbial resistance to antimicrobial agents is one of the biggest public health issues of the
21st century. Antibiotic-resistant bacteria (ARB) cause more than 2.8 million antibiotic-resistant infections in the
U.S. each year, and more than 35,000 people die as a result. The principal ways of antibiotic resistance
development are related to the intrinsic bacteria’s ability to evolve rapidly through mutations to either modify
these targets or the pathways for their synthesis, alter or degrade the antibiotic, or pump the antibiotic out of the
cell. Moreover, of critical importance is that all of these resistance mechanisms are encoded by antibiotic
resistance genes (ARGs), which are stable molecules encoded in the DNA and can be passed to daughter cells
or transported by horizontal gene transfer to neighboring pathogens. Despite tremendous efforts utilizing a wide
range of antibiotic discovery platform strategies, their success has been at best incremental. Therefore, there is
a critical need to develop effective approaches to simultaneously eliminate both ARB and ARGs. Recently, the
use of nanomaterials with antimicrobial activity has been explored as a new alternative against ARB and ARGs.
Silver nanoparticles (AgNPs) have been reported to have myriad applications as antimicrobial agents. In
addition, photodynamic inactivation (PDI) is also a feasible strategy to eliminate ARB and ARGs. The remarkable
features of AgNPs such as large surface area, capability to carry and release Ag+ ions, and ability to modulate
the microbial influx/efflux pumps; and PDI like efficient generation of ROS and the fact that does not generate
further resistance make these treatment modalities a promising alternative for the inactivation of ARB and ARGs.
We hypothesize that by combining both approaches, PDI and AgNPs, in the same platform a synergistic effect
to eliminate ARB and destroy ARGs will be achieved. The main goal of this project is to develop a light-activated
silver nanoparticulate system for the effective treatment of ARB and ARGs. This project consists of three aims:
in Aim 1, we will synthesize and characterize protoporphyrin IX (PpIX)-loaded AgNPs. This aim will demonstrate
that fabricating a rationally designed AgNP platform will enable a large payload of PpIX to be carried in a stable
formulation with tunable surface properties. For Aim 2, we will investigate the chemical and colloidal stability of
PpIX-AgNP materials under different culture medium and light irradiation conditions. This aim will provide key
information for the optimization of the platform and the influence of the environment on the generation of ROS
and Ag+ ions. Finally, in Aim 3, we will study the antimicrobial efficacy of PpIX-AgNPs against a panel of ARB,
the ARGs degradation kinetics and the nanoparticles cytotoxicity in mammalian cells. The information obtained
in this aim will allow us to move forward this platform to therapeutic applications.