Rapid evolution of silver nanoparticle resistance in Escherichia coli

Abstract

The recent exponential increase in the use of engineered nanoparticles (eNPs) means both greater intentional and unintentional exposure of eNPs to microbes. Intentional use includes the use of eNPs as biocides. Unintentional exposure results from the fact that eNPs are included in a variety of commercial products (paints, sunscreens, cosmetics). Many of these eNPs are composed of heavy metals or metal oxides such as silver, gold, zinc, titanium dioxide, and zinc oxide. It is thought that since metallic/metallic oxide NPs impact so many aspects of bacterial physiology that it will difficult for bacteria to evolve resistance to them. This study utilized laboratory experimental evolution to evolve silver nanoparticle (AgNP) resistance in the bacterium Escherichia coli (K-12 MG1655), a bacterium that does not harbor any known silver resistance elements. After 225 generations of exposure to the AgNP environment, the treatment populations demonstrated greater fitness vs. control strains as measured by optical density (OD) and colony forming units (CFU) in the presence of varying concentrations of 10 nm citrate-coated silver nanoparticles (AgNP) or silver nitrate (AgNO3). Genomic analysis shows that changes associated with AgNP resistance were already accumulating within the treatment populations by generation 100, and by generation 200 three mutations had swept to high frequency in the AgNP resistance stocks. This study indicates that despite previous claims to the contrary bacteria can easily evolve resistance to AgNPs, and this occurs by relatively simple genomic changes. These results indicate that care should be taken with regards to the use of eNPs as biocides as well as with regards to unintentional exposure of microbial communities to eNPs in waste products.

Mechanistic Basis of Antimicrobial Actions of Silver Nanoparticles

“…However, similar to antibiotics, prolonged exposure of bacteria to AgNPs may result in the development of resistant bacterial cells. For instance, E. coli K12 MG1655 strain has developed resistance toward AgNPs; however, the bacterium does not possess any Ag-resistance element (Graves et al, 2015). It is therefore necessary in future to carefully examining the development of Ag-resistance in bacteria.…”

Nanomaterials for alternative antibacterial therapy

“…While most metal-based NPs are microbicidal to an array of bacteria, genetic alterations in bacteria may result in rapid evolution of resistance to Ag NPs, 31 whereas Al 2 O 3 NPs trigger increased expression of conjugation-promoting genes, thus promoting horizontal transfer of antibiotic resistance genes. NPs have been tailored to subdue resistance …”

“…[28][29][30] On the other hand, upsurge in resistance to Ag NPs has been reported due to genetic alterations in bacteria. 31 The deposition of silver 32 The high toxicity of CuO NPs causes oxidative lesions, while DNA damage induced by ZnO and TiO 2 NPs limits the efficacy of these NPs. Nonetheless, NPs have emerged as alternative antimicrobial approach to combat biofilms and for treating severe bacterial infections.…”

An experiment-based model quantifying antimicrobial activity of silver nanoparticles onEscherichia coli

“…30 While some studies reported that metal nanoparticles did not result in obvious resistance in bacteria aer long-term exposure to them, 12,24 others found the opposite: Agresistant or metal nanoparticle-resistant bacteria can occur in a variety of circumstances and environments. [31][32][33][34] To help to avoid overdose and unnecessary exposure of these nanomaterials, it is important to understand the antimicrobial mechanism of metal nanoparticles.…”