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

A New Convenient Method to Assess Antibiotic Resistance and Antimicrobial Efficacy against Pathogenic Clostridioides difficile Biofilms

Clostridioides difficile is a widely distributed anaerobic pathogen. C. difficile infection is a serious problem in healthcare. Its biofilms have been found to exhibit biocorrosivity, albeit very little, but sufficient for it to correlate with biofilm growth/health. This work demonstrated the use of a disposable electrochemical biofilm test kit using two solid-state electrodes (a 304 stainless steel working electrode, and a graphite counter electrode, which also served as the reference electrode) in a 10 mL serum vial. It was found that the C. difficile 630∆erm Adp-4 mutant had a minimum inhibitory concentration (MIC) for vancomycin twice that of the 630∆erm wild type strain in biofilm prevention (2 ppm vs. 1 ppm by mass) on 304 stainless steel. Glutaraldehyde, a commonly used hospital disinfectant, was found ineffective at 2% (w/w) for the prevention of C. difficile 630∆erm wild type biofilm formation, while tetrakis(hydroxymethyl)phosphonium sulfate (THPS) disinfectant was very effective at 100 ppm for both biofilm prevention and biofilm killing. These antimicrobial efficacy data were consistent with sessile cell count and biofilm imaging results. Furthermore, the test kit provided additional transient biocide treatment information. It showed that vancomycin killed C. difficile 630∆erm wild type biofilms in 2 d, while THPS only required minutes.

Electrically polarized nanoscale surfaces generate reactive oxygenated and chlorinated species for deactivation of microorganisms

Because of the decreasing supply of new antibiotics, recent outbreaks of infectious diseases, and the emergence of antibiotic-resistant microorganisms, it is imperative to develop new effective strategies for deactivating a broad spectrum of microorganisms and viruses. We have implemented electrically polarized nanoscale metallic (ENM) coatings that deactivate a wide range of microorganisms including Gram-negative and Gram-positive bacteria with greater than 6-log reduction in less than 10 minutes of treatment. The electrically polarized devices were also effective in deactivating lentivirus and Candida albicans. The key to the high deactivation effectiveness of ENM devices is electrochemical production of micromolar cuprous ions, which mediated reduction of oxygen to hydrogen peroxide. Formation of highly damaging species, hydroxyl radicals and hypochlorous acid, from hydrogen peroxide contributed to antimicrobial properties of the ENM devices. The electric polarization of nanoscale coatings represents an unconventional tool for deactivating a broad spectrum of microorganisms through in situ production of reactive oxygenated and chlorinated species.

Mitigation of galvanized steel biocorrosion by Pseudomonas aeruginosa biofilm using a biocide enhanced by trehalase

Pseudomonas aeruginosa is a facultative bacterium that is pathogenic. It is ubiquitous in the environment including air handling systems. It causes microbiologically influenced corrosion (MIC) aerobically and anaerobically. In this work, P. aeruginosa was grown as a nitrate reducing bacterium (NRB) in Luria-Bertani medium with KNO3 at 37 °C. Trehalase, an enzyme which plays a crucial role in biofilm formation was found to enhance the treatment of P. aeruginosa biofilm and its MIC against galvanized steel by tetrakis-hydroxymethyl phosphonium sulfate (THPS) green biocide. After a 7-d incubation, 30 ppm (w/w) trehalase reduced sessile cell count by 0.8-log, and it also reduced galvanized steel weight loss by 14%, compared to 2.3-log and 39%, respectively for the 30 ppm THPS treatment. The combination of 30 ppm THPS + 30 ppm trehalase reduced sessile cell count further by 0.1-log and weight loss by 13% compared to using THPS alone. Electrochemical corrosion measurements supported weight loss results. The injection of 20 ppm riboflavin into a 3-d P. aeruginosa broth failed to accelerate the corrosion rate, suggesting that nitrate reducing P. aeruginosa MIC of galvanized steel did not belong to extracellular electron transfer-MIC, because Zn was hydrolyzed after the microbe damaged the passive film.

Pristine, Ni- and Zn-Doped CuSe Nanoparticles: An Antimicrobial, Antioxidant, and Cytotoxicity Study

The strategy of chemical coprecipitation is implemented to synthesize nanoparticles of pristine CuSe, 5 and 10% Ni-doped CuSe, and 5 and 10% Zn-doped CuSe. All of the nanoparticles are found to be near stoichiometric by the evaluation of X-ray energy using electron dispersion spectra, and the elemental mapping shows uniform distribution. By X-ray diffraction examination, all of the nanoparticles are identified as being single-phase and having a hexagonal lattice structure. Field emission microscopy with electrons in both scanning and transmission modes affirmed the spherical configuration of the nanoparticles. The crystalline nature of the nanoparticles is confirmed by the presence of spot patterns observed in the selected area electron diffraction patterns. The observed d value matches well with the d value of the CuSe hexagonal (102) plane. Findings from dynamic light scattering reveal the size distribution of nanoparticles. The nanoparticle's stability is investigated by ζ potential measurements. Pristine and Ni-doped CuSe nanoparticles exhibit ζ potential values in the preliminary stability band of ±10 to ±30 mV, while Zn-doped nanoparticles feature moderate stability levels of ±30 to ±40 mV. The potent antimicrobial effects of synthesized nanoparticles are studied against Staphylococcus aureus, Pseudomonas aeruginosa, Proteus vulgaris, Enterobacter aerogenes, and Escherichia coli bacteria. The 2,2-diphenyl-1-picrylhydrazyl scavenging test is used to investigate the nanoparticle's antioxidant activities. The results showed the highest activity for control (Vitamin C) with an IC₅₀ value of 43.6 μg/mL, while the lowest for Ni-doped CuSe nanoparticles with an IC₅₀ value of 106.2 μg/mL. Brine shrimps are utilized for in vivo cytotoxicity evaluation of the synthesized nanoparticles, which demonstrates that 10% Ni- and 10% Zn-doped CuSe nanoparticles are more damaging on brine shrimp instead on other nanoparticles with a 100% mortality rate. The lung cancer cell line of human (A549) is used to investigate in vitro cytotoxicity. The results indicate that pristine CuSe nanoparticles are more effective in the context of cytotoxicity against the A549 cell lines, possessing an IC₅₀ of 488 μg/mL. The particulars of the outcomes are explained in depth.

Evaluation of TiO2 Nanoparticles Physicochemical Parameters Associated with their Antimicrobial Applications

Titanium dioxide nanoparticles (TiO2NPs) usage is increasing in everyday consumer products, hence, assessing their toxic impacts on living organisms and environment is essential. Various studies have revealed the significant role of TiO2NPs physicochemical properties on their toxicity. However, TiO2NPs are still poorly characterized with respect to their physicochemical properties, and environmental factors influencing their toxicity are either ignored or are too complex to be assessed under laboratory conditions. The outcomes of these studies are diverse and inconsistent due to lack of standard protocols. TiO2NPs toxicity also differs for in vivo and in vitro systems, which must also be considered during standardization of protocols to maintain uniformity and reproducibility of results. This review critically evaluates impact of different physicochemical parameters of TiO2NPs and other experimental conditions, employed in different laboratories in determining their toxicity towards bacteria. These important observations may be helpful in evaluation of environmental risks posed by these nanoparticles and this can further assist regulatory bodies in policymaking.

Multidrug-Resistant Bacterial Pathogens and Public Health: The Antimicrobial Effect of Cyanobacterial-Biosynthesized Silver Nanoparticles

Background: Cyanobacteria are considered as green nano-factories. Manipulation of the size of biogenic silver nanoparticles is needed to produce particles that suit the different applications such as the use as antibacterial agents. The present study attempts to manipulate the size of biosynthesized silver nanoparticles produced by cyanobacteria and to test the different-sized nanoparticles against pathogenic clinical bacteria. Methods: Cyanothece-like. coccoid unicellular cyanobacterium was tested for its ability to biosynthesize nanosilver particles of different sizes. A stock solution of silver nitrate was prepared from which three different concentrations were added to cyanobacterial culture. UV-visible spectroscopy and FTIR were conducted to characterize the silver nanoparticles produced in the cell free filtrate. Dynamic Light Scattering (DLS) was performed to determine the size of the nanoparticles produced at each concentration. The antimicrobial bioassays were conducted on broad host methicillin-resistant Staphylococcus aureus (MRSA), and Streptococcus sp., was conducted to detect the nanoparticle size that was most efficient as an antimicrobial agent. Results. The UV-Visible spectra showed excellent congruence of the plasmon peak characteristic of nanosilver at 450 nm for all three different concentrations, varying peak heights were recorded according to the concentration used. The FTIR of the three solutions revealed the absence of characteristic functional groups in the solution. All three concentrations showed spectra at 1636 and 2050–2290 nm indicating uniformity of composition. Moreover, DLS analysis revealed that the silver nanoparticles produced with lowest concentration of precursor AgNO₃ had smallest size followed by those resulting from the higher precursor concentration. The nanoparticles resulting from highest concentration of precursor AgNO₃ were the biggest in size and tending to agglomerate when their size was above 100 nm. The three types of differently-sized silver nanoparticles were used against two bacterial pathogenic strains with broad host range; MRSA-(Methicillin-resistant Staphylococcus aureus) and Streptococcus sp. The three types of nanoparticles showed antimicrobial effects with the smallest nanoparticles being the most efficient in inhibiting bacterial growth. Discussion: Nanosilver particles biosynthesized by Cyanothece-like cyanobacterium can serve as antibacterial agent against pathogens including multi-drug resistant strains. The most appropriate nanoparticle size for efficient antimicrobial activity had to be identified. Hence, size-manipulation experiment was conducted to find the most effective size of nanosilver particles. This size manipulation was achieved by controlling the amount of starting precursor. Excessive precursor material resulted in the agglomeration of the silver nanoparticles to a size greater than 100 nm. Thereby decreasing their ability to penetrate into the inner vicinity of microbial cells and consequently decreasing their antibacterial potency. Conclusion: Antibacterial nanosilver particles can be biosynthesized and their size manipulated by green synthesis. The use of biogenic nanosilver particles as small as possible is recommended to obtain effective antibacterial agents.

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

The increasing release of nanomaterials has attracted significant concerns for human and environmental health. Similarly, the dissemination of antimicrobial resistance (AMR) is a global health crisis affecting approximately 700,000 people a year. However, a knowledge gap persists between the spread of AMR and nanomaterials. This study aims to fill this gap by investigating whether and how nanomaterials could directly facilitate the dissemination of AMR through horizontal gene transfer. Our results show that commonly-used nanoparticles (NPs) (Ag, CuO and ZnO NPs) and their ion forms (Ag⁺, Cu²⁺ and Zn²⁺) at realistic concentrations within aquatic environments can significantly promote the transformation of extracellular antibiotic resistance genes in Acinetobacter baylyi ADP1 by a factor of 11.0-folds, which is comparable to the effects of antibiotics. The enhanced transformation by Ag NPs/Ag⁺ and CuO NPs/Cu²⁺ was primarily associated with the overproduction of reactive oxygen species and cell membrane damage. ZnO NPs/Zn²⁺ might increase the natural transformation rate by stimulating the stress response and ATP synthesis. All tested NPs/ions resulted in upregulating the competence and SOS response-associated genes. These findings highlight a new concern that nanomaterials can speed up the spread of AMR, which should not be ignored when assessing the holistic risk of nanomaterials.

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

Resistance to antimicrobial agents has been alarming in recent years and poses a huge public health threat globally according to the WHO. The increase in morbidity and mortality resulting from microbial infections has been attributed to the emergence of multidrug-resistant microbes. Associated with the increase in multidrug resistance is the lack of new and effective antimicrobials. This has led to global initiatives to identify novel and more effective antimicrobial agents in addition to discovering novel and effective drug delivery and targeting methods. The use of nanoparticles as novel biomaterials to fully achieve this feat is currently gaining global attention. Nanoparticles could become an indispensable viable therapeutic option for treating drug-resistant infections. Of all the nanoparticles, the metals and metal oxide nanoparticles appear to offer the most promise and have attracted tremendous interest from many researchers. Moreover, the use of nanomaterials in photothermal therapy has received considerable attention over the years. This review provides current insight on antimicrobial resistance as well as the mechanisms of nanoparticle antibacterial activity. It offers an in-depth review of all the recent findings in the use of nanomaterials as agents against multi-resistant pathogenic bacteria. Also, nanomaterials that can respond to light stimuli (photothermal therapy) to kill microbes and facilitate enhanced drug delivery and release are discussed. Moreover, the synergistic interactions of nanoparticles with antibiotics and other nanomaterials, microbial adaptation strategies to nanoparticles, current challenges, and future prospects were extensively discussed.

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

Resistance to antimicrobial agents has been alarming in recent years and poses a huge public health threat globally according to the WHO. The increase in morbidity and mortality resulting from microbial infections has been attributed to the emergence of multidrug-resistant microbes. Associated with the increase in multidrug resistance is the lack of new and effective antimicrobials. This has led to global initiatives to identify novel and more effective antimicrobial agents in addition to discovering novel and effective drug delivery and targeting methods. The use of nanoparticles as novel biomaterials to fully achieve this feat is currently gaining global attention. Nanoparticles could become an indispensable viable therapeutic option for treating drug-resistant infections. Of all the nanoparticles, the metals and metal oxide nanoparticles appear to offer the most promise and have attracted tremendous interest from many researchers. Moreover, the use of nanomaterials in photothermal therapy has received considerable attention over the years. This review provides current insight on antimicrobial resistance as well as the mechanisms of nanoparticle antibacterial activity. It offers an in-depth review of all the recent findings in the use of nanomaterials as agents against multi-resistant pathogenic bacteria. Also, nanomaterials that can respond to light stimuli (photothermal therapy) to kill microbes and facilitate enhanced drug delivery and release are discussed. Moreover, the synergistic interactions of nanoparticles with antibiotics and other nanomaterials, microbial adaptation strategies to nanoparticles, current challenges, and future prospects were extensively discussed.

Label-Free Proteomic Approach to Study the Non-lethal Effects of Silver Nanoparticles on a Gut Bacterium

Among all the food-related nanoparticles consumed every day, silver nanoparticles (AgNPs) have become one of the most commonly utilized because of their antimicrobial properties. Despite their common use, the effects of sublethal concentrations of AgNPs, especially on gut biofilms, have been poorly investigated. To address this issue, we investigated in vitro the proteomic response of a monospecies Escherichia coli gut biofilm to chronic and acute exposures in sublethal concentrations of AgNPs. We used a new gel- and label-free proteomic approach based on shotgun nanoflow liquid chromatography-tandem mass spectrometry. This approach allows a quantification of the whole proteome at a dynamic range that is higher than the traditional proteomic investigation. To assess all different possible exposure scenarios, we compared the biofilm proteome of four treatments: (i) untreated cells for the control treatment, (ii) cells treated with 1 μg/ml AgNPs for 24 h for the acute treatment, (iii) cells grown with 1 μg/ml AgNPs for 96 h for the chronic treatment, and (iv) cells grown in the presence of 1 μg/ml AgNPs for 72 h and then further treated for 24 h with 10 μg/ml AgNPs for the chronic + acute treatment. Among the 1,917 proteins identified, 212 were significantly differentially expressed proteins. Several pathways were altered including biofilm formation, bacterial adhesion, stress response to reactive oxygen species, and glucose utilization.

Molecular Mechanisms of Bacterial Resistance to Metal and Metal Oxide Nanoparticles

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.

Ferroxidase-like and antibacterial activity of PtCu alloy nanoparticles

Many metal nanoparticles are reported to have intrinsic enzyme-like activities and offer great potential in chemical and biomedical applications. In this study, PtCu alloy nanoparticles (NPs), synthesized through hydrothermal treatment of Cu²⁺ and Pt²⁺ in an aqueous solution, were evaluated for ferroxidase-like and antibacterial activity. Electron spin resonance (ESR) spectroscopy and colorimetric methods were used to demonstrate that PtCu NPs exhibited strong ferroxidase-like activity in a weakly acidic environment and that this activity was not affected by the presence of most other ions, except silver. Based on the color reaction of salicylic acid in the presence of Fe³⁺, we tested the ferroxidase-like activity of PtCu NPs to specifically detect Fe²⁺ in a solution of an oral iron supplement and compared these results with data acquired from atomic absorption spectroscopy and the phenanthroline colorimetric method. The results showed that the newly developed PtCu NPs detection method was equivalent to or better than the other two methods used for Fe²⁺ detection. The antibacterial experiments showed that PtCu NPs have strong antibacterial activity against Staphylococcus aureus and Escherichia coli. Herein, we demonstrate that the peroxidase-like activity of PtCu NPs can catalyze H₂O₂ and generate hydroxyl radicals, which may elucidate the antibacterial activity of the PtCu NPs against S. aureus and E. coli. These results showed that PtCu NPs exhibited both ferroxidase- and peroxidase-like activity and that they may serve as convenient and efficient NPs for the detection of Fe²⁺ and for antibacterial applications.

Physiological and transcriptomic analyses reveal CuO nanoparticle inhibition of anabolic and catabolic activities of sulfate-reducing bacterium

The widespread use of CuO nanoparticles (NPs) results in their continuous release into the environment, which could pose risks to public health and to microbial ecosystems. Following consumption, NPs will initially enter into sewer systems and interact with and potentially influence sewer microbial communities. An understanding of the response of microbes in sewers, particularly sulfate-reducing bacteria (SRB), to the CuO NPs induced stress is important as hydrogen sulfide produced by SRB can cause sewer corrosion and odour emissions. In this study, we elucidated how the anabolic and catabolic processes of a model SRB, Desulfovibrio vulgaris Hidenborough (D. vulgaris), respond to CuO NPs. Physiological analyses indicated that the exposure of the culture to CuO NPs at elevated concentrations (>50 mg/L) inhibited both its anabolic and catabolic activities, as revealed by lowered cell proliferation and sulfate reduction rate. The antibacterial effects of CuO NPs were mainly attributed to the overproduction of reactive oxygen species. Transcriptomic analysis indicated that genes encoding for flagellar assembly and some genes involved in electron transfer and respiration were down-regulated, while genes for the ferric uptake regulator (Fur) were up-regulated. Moreover, the CuO NPs exposure significantly up-regulated genes involved in protein synthesis and ATP synthesis. These results suggest that CuO NPs inhibited energy conversion, cell mobility, and iron starvation to D. vulgaris. Meanwhile, D. vulgaris attempted to respond to the stress of CuO NPs by increasing protein and ATP synthesis. These findings offer new insights into the bacterial-nanoparticles interaction at the transcriptional level, and advance our understanding of impacts of CuO NPs on SRB in the environment.

Antibacterial activity and mechanism of silver nanoparticles against multidrug-resistant Pseudomonas aeruginosa

BACKGROUND

The threat of drug-resistant Pseudomonas aeruginosa requires great efforts to develop highly effective and safe bactericide.

OBJECTIVE

This study aimed to investigate the antibacterial activity and mechanism of silver nanoparticles (AgNPs) against multidrug-resistant P. aeruginosa.

METHODS

The antimicrobial effect of AgNPs on clinical isolates of resistant P. aeruginosa was assessed by minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). In multidrug-resistant P. aeruginosa, the alterations of morphology and structure were observed by the transmission electron microscopy (TEM); the differentially expressed proteins were analyzed by quantitative proteomics; the production of reactive oxygen species (ROS) was assayed by H2DCF-DA staining; the activity of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) was chemically measured and the apoptosis-like effect was determined by flow cytometry.

RESULTS

Antimicrobial tests revealed that AgNPs had highly bactericidal effect on the drug-resistant or multidrug-resistant P. aeruginosa with the MIC range of 1.406-5.625 µg/mL and the MBC range of 2.813-5.625 µg/mL. TEM showed that AgNPs could enter the multidrug-resistant bacteria and impair their morphology and structure. The proteomics quantified that, in the AgNP-treated bacteria, the levels of SOD, CAT, and POD, such as alkyl hydroperoxide reductase and organic hydroperoxide resistance protein, were obviously high, as well as the significant upregulation of low oxygen regulatory oxidases, including cbb3-type cytochrome c oxidase subunit P2, N2, and O2. Further results confirmed the excessive production of ROS. The antioxidants, reduced glutathione and ascorbic acid, partially antagonized the antibacterial action of AgNPs. The apoptosis-like rate of AgNP-treated bacteria was remarkably higher than that of the untreated bacteria (P<0.01).

CONCLUSION

This study proved that AgNPs could play antimicrobial roles on the multidrug-resistant P. aeruginosa in a concentration- and time-dependent manner. The main mechanism involves the disequilibrium of oxidation and antioxidation processes and the failure to eliminate the excessive ROS.

Nanotoxicity of engineered nanomaterials (ENMs) to environmentally relevant beneficial soil bacteria - a critical review

Deposition of engineered nanomaterials (ENMs) in various environmental compartments is projected to continue rising exponentially. Terrestrial environments are expected to be the largest repository for environmentally released ENMs. Because ENMs are enriched in biosolids during wastewater treatment, agriculturally applied biosolids facilitate ENM exposure of key soil micro-organisms, such as plant growth-promoting rhizobacteria (PGPR). The ecological ramifications of increasing levels of ENM exposure of terrestrial micro-organisms are not clearly understood, but a growing body of research has investigated the toxicity of ENMs to various soil bacteria using a myriad of toxicity end-points and experimental procedures. This review explores what is known regarding ENM toxicity to important soil bacteria, with a focus on ENMs which are expected to accumulate in terrestrial ecosystems at the highest concentrations and pose the greatest potential threat to soil micro-organisms having potential indirect detrimental effects on plant growth. Knowledge gaps in the fundamental understanding of nanotoxicity to bacteria are identified, including the role of physicochemical properties of ENMs in toxicity responses, particularly in agriculturally relevant micro-organisms. Strategies for improving the impact of future research through the implementation of in-depth ENM characterization and use of necessary experimental controls are proposed. The future of nanotoxicological research employing microbial ecoreceptors is also explored, highlighting the need for continued research utilizing bacterial isolates while concurrently expanding efforts to study ENM-bacteria interactions in more complex environmentally relevant media, e.g. soil. Additionally, the particular importance of future work to extensively examine nanotoxicity in the context of bacterial ecosystem function, especially of plant growth-promoting agents, is proposed.

Induction of Escherichia coli into a VBNC state through chlorination/chloramination and differences in characteristics of the bacterium between states

Many pathogens can enter into a viable but nonculturable (VBNC) state in response to harsh environmental stresses. Bacteria in this state can retain certain features of viable cells, such as cellular integrity, metabolic activity, or virulence and may present health risks associated with drinking water. In this study, we investigated the ability of chlorination and chloramination, which are widely used methods to disinfect drinking water, to induce Escherichia coli into a VBNC state. After treatment with chlorine and chloramine at concentrations of 1, 2, 3, and 4 mg/L, the counts of culturable E. coli cells decreased from 10⁶ CFU/mL to 0 CFU/mL at 5-60 min post treatment. Meanwhile, viable cell counts were still approximately 10³-10⁵ cells/mL. These viable E. coli cells may be induced into a VBNC state by chlorination and chloramination. Scanning electron microscopy and laser confocal microscopy showed that some bacteria maintained cellular integrity, but the average length of VBNC cells was less than that of culturable cells. Respiratory activity of VBNC cells decreased approximately 50% relative to that of culturable cells. We also used heavy water (D₂O) combined with Raman microspectroscopy to show that E. coli in a VBNC state retained metabolic activity involving water (e.g. condensation reactions) at the single-cell level. Furthermore, soxR, gadA, and katG genes remained highly expressed, suggesting that VBNC cells were physiologically active. Finally, resuscitation of VBNC cells induced by chlorine in Luria-Bertani (LB) broth was identified by calculating the generation time. Results of this study will facilitate a better understanding of the health risks associated with VBNC bacteria and the development of more effective strategies for drinking water disinfection.

Application of the kinetic and isotherm models for better understanding of the behaviors of silver nanoparticles adsorption onto different adsorbents

It is the first time to do investigation the reliability and validity of thirty kinetic and isotherm models for describing the behaviors of adsorption of silver nanoparticles (AgNPs) onto different adsorbents. The purpose of this study is therefore to assess the most reliable models for the adsorption of AgNPs onto feasibility of an adsorbent. The fifteen kinetic models and fifteen isotherm models were used to test secondary data of AgNPs adsorption collected from the various data sources. The rankings of arithmetic mean were estimated based on the six statistical analysis methods of using a dedicated software of the MATLAB Optimization Toolbox with a least square curve fitting function. The use of fractal-like mixed 1, 2-order model for describing the adsorption kinetics and that of Fritz-Schlunder and Baudu models for describing the adsorption isotherms can be recommended as the most reliable models for AgNPs adsorption onto the natural and synthetic adsorbent materials. The application of thirty models have been identified for the adsorption of AgNPs to clarify the usefulness of both groups of the kinetic and isotherm equations in the rank order of the levels of accuracy, and this significantly contributes to understandability and usability of the proper models and makes to knowledge beyond the existing literatures.

Stress Responses of Aquatic Plants to Silver Nanoparticles

Silver nanoparticles (AgNPs) are increasingly used in consumer products, biotechnology, and medicine, and are released into aquatic ecosystems through wastewater discharge. This study investigated the phytotoxicity of AgNPs to aquatic plants, Egeria densa and Juncus effusus by measuring physiologic and enzymatic responses to AgNP exposure under three release scenarios: two chronic (8.7 mg, weekly) exposures to either zerovalent AgNPs or sulfidized silver nanoparticles; and a pulsed (450 mg, one-time) exposure to zerovalent AgNPs. Plant enzymatic and biochemical stress responses were assessed using superoxide dismutase (SOD) and peroxidase (POD) activity, malondialdehyde (MDA) concentrations and chlorophyll content as markers of defense and phytotoxicity, respectively. The high initial pulse treatment resulted in rapid changes in physiological characteristics and silver concentration in plant tissue at the beginning of each AgNPs exposure (6 h, 36 h, and 9 days), while continuous AgNP and sulfidized AgNP chronic treatments gave delayed responses. Both E. densa and J. effusus enhanced their tolerance to AgNPs toxicity by increasing POD and SOD activities to scavenge free radicals but at different growth phases. Chlorophyll did not change. After AgNPs exposure, MDA, an index of membrane damage, was higher in submerged E. densa than emergent J. effusus, which suggested that engineered nanoparticles exerted more stress to submerged macrophytes.