Role of bacterial motility in differential resistance mechanisms of silver nanoparticles and silver ions

Abstract

Unlike conventional antimicrobials, the study of bacterial resistance to silver nanoparticles (AgNPs) remains in its infancy and the mechanism(s) through which it evolves are limited and inconclusive. The central question remains whether bacterial resistance is driven by the AgNPs, released Ag(I) ions or a combination of these and other factors. Here, we show a specific resistance in an Escherichia coli K-12 MG1655 strain to subinhibitory concentrations of AgNPs, and not Ag(I) ions, as indicated by a statistically significant greater-than-twofold increase in the minimum inhibitory concentration occurring after eight repeated passages that was maintained after the AgNPs were removed and reintroduced. Whole-population genome sequencing identified a cusS mutation associated with the heritable resistance that possibly increased silver ion efflux. Finally, we rule out the effect of particle aggregation on resistance and suggest that the mechanism of resistance may be enhanced or mediated by flagellum-based motility.

Quaternized Polydopamine Coatings for Anchoring Molecularly Dispersed Broad-Spectrum Antimicrobial Silver Salts

“…It is a well-known fact that microbes develop resistance over a period of time upon continuous exposure to the antimicrobial substance . In the case of Gram-negative bacteria, the presence of the sil operon gene encoded with two efflux pumps and two periplasmic silver-binding chaperone proteins has been shown to act synergistically in driving out the silver ions. , Therefore, we performed the antibacterial resistance study using E. coli and S. aureus up to 10 passages, wherein ∼30% of the cells were killed in each cycle and thereby allowing the viable colonies for further growth to check any mutation acquired during the subsequent passages. The antibacterial resistance was monitored through the optical density measurements at the end of each passage, and the results are presented in Figure S7.…”

“…37−39 A recent study demonstrated that the propensity of microbial mutation is substantially less with ionic silver over silver nanoparticles and thereby highlighted the advantage of ionic silver. 40 Although several research works have been actively pursued to develop silver-based coatings to encounter the disinfection challenges, the majority of them are focused on silver nanoparticles or metallic silver coatings. 41−43 Silvercontaining photocatalysts have also been developed to achieve a high bactericidal performance, but their high-temperature synthesis and difficulties associated with additive-free coatings limit their application domains.…”

“…On a different note, addressing the challenges associated with nosocomial infection has become one of the topmost priorities in the health sector. − Establishing efficient antimicrobial coatings over the frequently touched surfaces has been considered to be an essential strategy to combat the spread of microbial pathogenesis in hospital and crowded environment . Antibiotics and other chemical disinfectants are commonly used for this purpose; , however, this approach often leads to the incidence of drug-resistant pathogens that are more harmful. , Conventionally, it is known that silver nanoparticles and ionic silver exhibit a high antimicrobial property even at ultralow concentrations. − A recent study demonstrated that the propensity of microbial mutation is substantially less with ionic silver over silver nanoparticles and thereby highlighted the advantage of ionic silver . Although several research works have been actively pursued to develop silver-based coatings to encounter the disinfection challenges, the majority of them are focused on silver nanoparticles or metallic silver coatings. − Silver-containing photocatalysts have also been developed to achieve a high bactericidal performance, but their high-temperature synthesis and difficulties associated with additive-free coatings limit their application domains. , Thus, it is imperative to develop strategies that yield highly dispersed ionic silver over a material surface. − …”

Antimicrobial Resistance Development Pathways in Surface Waters and Public Health Implications

“…Additionally, AgNPs were effective in disrupting the morphology and structure and inhibiting biofilm formation of multidrug-resistant Pseudomonas aeruginosa [ 156 , 157 ]. In contrast, recent studies have shown the potential of AgNPs to stimulate AR in Escherichia coli K-12 MG1655 strain and the transfer of ARGs from E. coli K-12 LE392 to Pseudomonas putida KT2440 at environmentally relevant concentrations [ 158 , 159 ]. The results of these studies demonstrate that microorganisms are gradually becoming resistant to AgNPs as large quantities of the nanoparticles are produced annually and incorporated into consumer products worldwide.…”

Five nanometer size highly positive silver nanoparticles are bactericidal targeting cell wall and adherent fimbriae expression

“…Moreover, bacterial isolates lacking expression of fimbriae have demonstrated reduced growth, adhesion, biofilm formation and virulence, thereby resulting in low infections and improved survival in animal models and humans when infected with the virulent strains 8 . Hence, a need for better antimicrobial agents that can specifically target the cell wall and/or adherent fimbriae expression cannot be overstated, and engineered nanomaterials (ENMs) may have the potential to serve as the next generation antimicrobial agent 9 .…”