Aerobic condition enhances bacteriostatic effects of silver nanoparticles in aquatic environment: an antimicrobial study on Pseudomonas aeruginosa

Abstract

The intensive applications of silver nanoparticles (AgNPs) inevitably cause continuous release of such materials into environments, as a consequence posing potential risks to microbial communities in engineered or natural ecosystems. However, the magnitude of antibacterial capacity of nanoparticles is still inconclusive, owing to influential factors such as the size of nanoparticle, microbial species, or environmental conditions. To reveal whether the presence of air would alter AgNPs ecotoxicity, Pseudomonas aeruginosa PAO1, a facultative denitrifying bacterium and an opportunity pathogen, was used to study antibacterial assays under both anaerobic and aerobic conditions. The results indicate that the respiration status of P. aeruginosa affect the ecotoxicity of AgNPs. P. aeruginosa cultured under aerobic condition were more susceptible to AgNPs than that under anaerobic condition. Aerobic condition greatly enhanced bacteriostatic effects of AgNPs but not their bactericidal effects, as the ratio of viable but nonculturable (VBNC) bacteria remained above 90% when 5 mg L −1 AgNPs applied. Our findings offer further understanding for the degree of toxicity of nanoparticles on microbial ecosystems and underscore the importance of exposure condition (e.g. oxygen) in the mode of action of AgNPs.Silver nanoparticles (AgNPs) have been widely used in consumer products such as textile, cosmetics, and medical products, due to their excellent antibacterial, optical, and electronic properties [1][2][3] . AgNPs are the most popular nanoparticles in markets, which accounts for about 50% of commercial nanoproducts 4 . It is estimated that approximate 500 tons of AgNPs were produced each year worldwide 5,6 . As being incorporated in fabric and personal care products, the processes of fabrication and consumption thereby can release AgNPs from consumer products to sewage, eventually entering environment. Thus, it represents a potential risk to a great variety of organisms in natural or engineered ecosystems, including wastewater treatment plants (WWTPs).AgNPs have shown great antibacterial activities against various microbes. Choi et al. 7 reported that the respiration of autotrophic nitrifiers in a continuously stirred tank reactor was inhibited by 86% at 1 mg L −1 of AgNPs. Tan et al. 8 documented that AgNPs at 300 µg L −1 decreased nitrifying efficiency from 98% to 15%. In addition, Li et al. 9 showed that a commercial AgNPs at 10 mg L −1 was the miminum inhibitory concentration (MIC) to Escherichia coli, whereas a synthesized AgNPs exhibited 100% killing of E. coli when added at 4.5 mg L −110 . According to these previous studies 7-11 , the concentration of AgNPs that will cause toxic impacts on microbes, ranged from µg L −1 to mg L −1 . Such an inconclusive antibacterial capacity of nanoparticles may be associated with different exposure conditions or microorganism types, which may alter the antibacterial activity of nanoparticles. Some studies [12][13][14][15] suggested that the susceptibility of microbes, microbial adapt...

Insights of metallic nanoparticles and ions in accelerating the bacterial uptake of antibiotic resistance genes

“…1A and B), indicating that NPs promote the plasmid transformation differently than their associated ionic counterparts due to the unique physicochemical properties of NPs. Similar phenomena have also been observed previously in Ag NPs mediated toxicity (Chen et al, 2017) and conjugative gene transfer (Lu et al, 2020), where NPs induced a higher toxicity and an enhanced conjugative gene transfer frequency than their associated ionic counterparts.…”

<p>Antibacterial activity and mechanism of silver nanoparticles against multidrug-resistant <em>Pseudomonas aeruginosa</em></p>

“…42 Another study on facultative denitrifying P. aeruginosa PAO1 revealed that under anaerobic conditions, AgNPs had antibacterial impact on P. aeruginosa, but under aerobic conditions, this impact was dramatically enhanced. 43 pathway, other mechanisms exist in the course of AgNPs fighting against microorganisms.…”

Nanoparticles as therapeutic options for treating multidrug-resistant bacteria: research progress, challenges, and prospects

“…Reproduced from Wu et al (2019) with permission the chance of ions release. It was also reported by Chen et al (2017) that exposure of microbes to AgNps under anaerobic condition decreases the antimicrobial activity of nanoparticles (Chen et al 2017). Moreover, the alteration in environmental conditions can cause a spontaneous rise in mutation and also trigger genome plasticity which can greatly facilitate resistance to antimicrobial agents and evolutions of strains with increased fitness.…”