Molecular Mechanisms of Bacterial Resistance to Metal and Metal Oxide Nanoparticles

Abstract

The increase in bacterial resistance to one or several antibiotics has become a global health problem. Recently, nanomaterials have become a tool against multidrug-resistant bacteria. The metal and metal oxide nanoparticles are one of the most studied nanomaterials against multidrug-resistant bacteria. Several in vitro studies report that metal nanoparticles have antimicrobial properties against a broad spectrum of bacterial species. However, until recently, the bacterial resistance mechanisms to the bactericidal action of the nanoparticles had not been investigated. Some of the recently reported resistance mechanisms include electrostatic repulsion, ion efflux pumps, expression of extracellular matrices, and the adaptation of biofilms and mutations. The objective of this review is to summarize the recent findings regarding the mechanisms used by bacteria to counteract the antimicrobial effects of nanoparticles.

Keywords: bacteria; nanoparticles; resistance.

Figure 1

The defense mechanisms of the bacteria against nanoparticles include the production of extra-cellular substances (like flagellin) with the ability to agglomerate nanoparticles, and the production of pigments (like pyocyanin) capable of inactivating the ions released by the nanoparticles.

Figure 2

Bacterial resistance to nanoparticles is due to the change of expression of genes and the presence of oxidative stress which causes a decrease in porins, activation of SOXR and OXYR (redox-sensitive transcriptional activators), change of the electric charge of the bacterial wall, overexpression of efflux systems and change in the synthesis of lipopolysaccharides. “↑ “upregulation, “↓” downregulation.