Effect of silver nanoparticles on Pseudomonas putida biofilms at different stages of maturity

Enhanced bacterial adhesion force by rifampicin resistance promotes microbial colonization on PE plastic compared to non-resistant biofilm formation

The microbial biofilm formed on plastics, is ubiquitous in the environment. However, the effects of antibiotic resistance on the development of the biofilm on plastics, especially with regard to initial cell attachment, remain unclear. In this study, we investigated the initial bacterial adhesion and subsequent biofilm growth of a rifampin (Rif) resistant E. coli (RRE) and a normal gram-positive B. subtilis on a typical plastic (polyethylene, PE). The experiments were conducted in different antibiotic solutions, including Rif, sulfamethoxazole (SMX), and kanamycin (KM), with concentrations ranging from 1 to 1000 μg/L to simulate different aquatic environments. The AFM-based single-cell adhesion force determination revealed that Rif resistance strengthened the adhesion force of RRE to PE in the environment rich in Rif rather than SMX and KM. The enhanced adhesion force may be due to the higher secretion of extracellular polymeric substances (EPS), particularly proteins, by RRE in the presence of Rif compared to the other two antibiotics. In addition, the higher ATP level of RRE would facilitate the initial adhesion and subsequent biofilm growth. Transcriptome analysis of RRE separately cultured in Rif and SMX environments demonstrated a clear correlation between the expression of Rif resistance and the augmented bacterial adhesion and cellular activity. Biofilm biomass analysis confirmed the promotion effect of Rif resistance on biofilm growth when compared to non-resistant biofilms, establishing a novel association with the augmentation of microbial adhesion force. Our study highlights concerns related to the dissemination of antibiotic resistance during microbial colonization on plastic that may arise from antibiotic resistance.

How similar is the antibacterial activity of silver nanoparticles coated with different capping agents?†

Silver nanoparticles (AgNPs) represent one of the most commercialised metal nanomaterials, with an extensive number of applications that span from antimicrobial products to electronics. Bare AgNPs are very susceptible to aggregation, and capping agents are required for their protection and stabilisation. The capping agents can endow new characteristics which can either improve or deteriorate AgNPs (bio)activity. In the present work, five different capping agents were studied as stabilizing agents for AgNPs: trisodium citrate (citrate), polyvinylpyrrolidone (PVP), dextran (Dex), diethylaminoethyl-dextran (Dex^DEAE) and carboxymethyl-dextran (Dex^CM). The properties of the AgNPs were studied using a set of methods, including transmission electron microscopy, X-ray diffraction, thermogravimetric analysis and ultraviolet-visible and infrared spectroscopy. Coated and bare AgNPs were also tested against Escherichia coli, methicillin-resistance Staphylococcus aureus and Pseudomonas aeruginosa to analyse their capacity to suppress bacterial growth and eradicate biofilms of clinically relevant bacteria. The results showed that all the capping agents endow long-term stability for the AgNPs in water; however, when the AgNPs are in bacterial culture media, their stability is highly dependent on the capping agent properties due to the presence of electrolytes and charged macromolecules such as proteins. The results also showed that the capping agents have a substantial impact on the antibacterial activity of the AgNPs. The AgNPs coated with the Dex and Dex^CM were the most effective against the three strains, due to their better stability which resulted in the release of more silver ions, better interactions with the bacteria and diffusion into the biofilms. It is hypothesized that the antibacterial activity of capped AgNPs is governed by a balance between the AgNPs stability and their ability to release silver ions. Strong adsorption of capping agents like PVP on the AgNPs endows higher colloidal stability in culture media; however, it can decrease the rate of Ag⁺ release from the AgNPs and reduce the antibacterial performance. Overall, this work presents a comparative study between different capping agents on the properties and antibacterial activity of AgNPs, highlighting the importance of the capping agent in their stability and bioactivity.

Nanosilver antibacterial activity is governed by a balance between the nanosilver stability and their ability to release/dope Ag⁺ to solution.

Growth suppression of bacteria by biofilm deterioration using silver nanoparticles with magnetic doping

Decades of antibiotic use and misuse have generated selective pressure toward the rise of antibiotic-resistant bacteria, which now contaminate our environment and pose a major threat to humanity. According to the evolutionary "Red queen theory", developing new antimicrobial technologies is both urgent and mandatory. While new antibiotics and antibacterial technologies have been developed, most fail to penetrate the biofilm that protects bacteria against external antimicrobial attacks. Hence, new antimicrobial formulations should combine toxicity for bacteria, biofilm permeation ability, biofilm deterioration capability, and tolerability by the organism without renouncing compatibility with a sustainable, low-cost, and scalable production route as well as an acceptable ecological impact after the ineluctable release of the antibacterial compound in the environment. Here, we report on the use of silver nanoparticles (NPs) doped with magnetic elements (Co and Fe) that allow standard silver antibacterial agents to perforate bacterial biofilms through magnetophoretic migration upon the application of an external magnetic field. The method has been proved to be effective in opening micrometric channels and reducing the thicknesses of models of biofilms containing bacteria such as Enterococcus faecalis, Enterobacter cloacae, and Bacillus subtilis. Besides, the NPs increase the membrane lipid peroxidation biomarkers through the formation of reactive oxygen species in E. faecalis, E. cloacae, B. subtilis, and Pseudomonas putida colonies. The NPs are produced using a one-step, scalable, and environmentally low-cost procedure based on laser ablation in a liquid, allowing easy transfer to real-world applications. The antibacterial effectiveness of these magnetic silver NPs may be further optimized by engineering the external magnetic fields and surface conjugation with specific functionalities for biofilm disruption or bactericidal effectiveness.

Deposition of polystyrene microplastics on bare or biofilm-coated silica analysed via QCM-D

The mobility of microplastics (MPs) in aqueous media is closely related to their environmental risk. The naturally occurring silica substrate surface in the aquatic environment is easily colonized by microorganisms and forms a biofilm, which may affect the migration and distribution of MPs. Herein, a typical MP, polystyrene (PS), and Pseudomonas fluorescens (P. fluorescens) biofilms were selected to study the deposition and release of pristine or ultraviolet (UV)-aged PS MPs on silica and biofilms under different ionic strengths using a quartz crystal microbalance dissipation (QCM-D) system. Statistical analyses of the deposition experiments revealed a significant impact of P. fluorescens biofilms on deposition (p = 0.0042). The deposition rate of weathered MPs on the biofilms was 4.0 ± 0.1 to 16.3 ± 0.6 times that on silica. A release experiment revealed that the biofilm reduced the release fraction (f_r) of weathered MPs by 34.5 ± 0.3 % compared to bare silica. In addition, the UV-ageing treatment reduced the deposition mass of MPs on the surface of silica by 27.6 ± 0.21 % compared to pristine microspheres. The analysis of the deposition mechanism revealed that the promotion and inhibition of biofilm or UV-ageing treatment on the deposition of microspheres could be attributed to the non-Derjaguin-Landau-Verwey-Overbeek (DLVO) force and the decreased electrostatic repulsion or the increased hydration repulsion, respectively.

Impact of synthetic silver nanoparticles on the biofilm microbial communities and wastewater treatment efficiency in experimental hybrid filter system treating municipal wastewater

Silver nanoparticles (AgNPs) threaten human and ecosystem health, and are among the most widely used engineered nanomaterials that reach wastewater during production, usage, and disposal phases. This study evaluated the effect of a 100-fold increase in collargol (protein-coated AgNP) and Ag⁺ ions concentrations in municipal wastewater on the microbial community composition of the filter material biofilms (FMB) and the purification efficiency of the hybrid treatment system consisting of vertical (VF) and horizontal (HF) subsurface flow filters. We found that increased amounts of collargol and AgNO₃ in wastewater had a modest effect on the prokaryotic community composition in FMB and did not significantly affect the performance of the studied system. Regardless of how Ag was introduced, 99.9% of it was removed by the system. AgNPs and AgNO₃ concentrations did not significantly affect the purification efficiency of the system. AgNO₃ induced a higher increase in the genetic potential of certain Ag resistance mechanisms in VFs than collargol; however, the increase in Ag resistance potential was similar for both substances in HF. Hence, the microbial community composition in biofilms of vertical and horizontal flow filters is largely resistant, resilient, or functionally redundant in response to AgNPs addition in the form of collargol.

Immobilized arginine/tryptophan-rich cyclic dodecapeptide on reduced graphene oxide anchored with manganese dioxide for microbial biofilm eradication

To avoid the accumulation of bacterial biofilms in water pipelines, it is critical to develop potent antimicrobial agents with good ability to reduce extracellular polymeric substances (EPS). In this study, cyclic dodecapeptides were synthesized, and different mutations for increasing the ratio of arginine (Arg) and tryptophan (Trp) were introduced. Separately, the synthesized dodecapeptides were immobilized on a reduced graphene oxide nanocomposite anchored with a hierarchical β-MnO₂ (RGO/β-MnO₂) hybrid. With a minimum inhibitory concentration of 0.97 g/mL, the immobilized Arg-Trp rich antimicrobial peptides (AMP) on RGO/MnO₂ nanocomposite, Cdp-4/RGO/MnO₂, showed superior efficacy against multidrug-resistant Pseudomonas aeruginosa ATCC 15692 (P. aeruginosa) planktonic cells. The immobilized Cdp-4/RGO/β-MnO₂ also eradicated the mature biofilm by 99% with a minimum inhibitory concentration value of 62.5 µg/mL with significant reduction of EPS. These characteristics allow the use of the immobilized Arg-Trp rich AMP as a promising antimicrobial agent against microbial biofilms, present in water distribution systems.

Benefits of Usage of Immobilized Silver Nanoparticles as Pseudomonas aeruginosa Antibiofilm Factors

The aim of this study was to assess the beneficial inhibitory effect of silver nanoparticles immobilized on SiO2 or TiO2 on biofilm formation by Pseudomonas aeruginosa-one of the most dangerous pathogens isolated from urine and bronchoalveolar lavage fluid of patients hospitalized in intensive care units. Pure and silver doped nanoparticles of SiO2 and TiO2 were prepared using a novel modified sol-gel method. Ten clinical strains of P. aeruginosa and the reference PAO1 strain were used. The minimal inhibitory concentration (MIC) was determined by the broth microdilution method. The minimal biofilm inhibitory concentration (MBIC) and biofilm formation were assessed by colorimetric assay. Bacterial enumeration was used to assess the viability of bacteria in the biofilm. Silver nanoparticles immobilized on the SiO2 and TiO2 indicated high antibacterial efficacy against P. aeruginosa planktonic and biofilm cultures. TiO2/Ag0 showed a better bactericidal effect than SiO2/Ag0. Our results indicate that the inorganic compounds (SiO2, TiO2) after nanotechnological modification may be successfully used as antibacterial agents against multidrug-resistant P. aeruginosa strains.

Transcriptional analysis of metabolic and virulence genes associated with biofilm formation in Piscirickettsia salmonis strains

Piscirickettsia salmonis is a facultative intracellular bacterium that generates piscirickettsiosis affecting salmonids in Chile. The bacterium has the adaptability to survive in the marine environment under multiple stressful conditions. In this sense, this work focused on the analysis of a gene battery associated with biofilm formation under different culture conditions and on the adaptability of this biofilm to different media. The results indicated that the strains LF-89, IBM-034 and IBM-040 were strong biofilm producers, evidencing adaptability to the media by increasing the amount of biofilm through successive growths. Transcript levels of six genes described in various bacteria and P. salmonis, considered to have metabolic functions, and playing a relevant role in biofilm formation, were analyzed to evaluate bacterial functionality in the biofilm. The genes mazE-mazF, implicated in biofilm and stress, were markedly overexpressed in the biofilm condition in the three strains. For its part, gene gltA, an indicator of metabolic activity and related to virulence inhibition in Salmonella typhimurium, also seems to restrain the pathogenesis process in P. salmonis by inhibiting the expression of the virulence-associated genes liso and tcf. Finally, the expression of the glnA gene suggests the use of glutamine as an essential element for the growth of the biofilm.

Silver nanoparticles effect on Artemia salina and Allium cepa organisms: influence of test dilution solutions on toxicity and particles aggregation

The objective of this study was to evaluate the effects of AgNPs on Artemia salina and Allium cepa, evaluating the influence of the dilution solutions on the particle behavior. The AgNPs were synthesized by chemical reduction of AgNO₃ (3 and 5 mmol L^-1) with sodium borohydride and stabilized with PVA (polyvinyl alcohol) and CMC (sodium carboxymethyl cellulose). The toxicity of AgNPs was evaluated in Artemia salina (mortality) using Meyer's solution as a diluent and in Allium cepa (chromosomal aberrations) using reconstituted hard water. AgNPs showed characteristic molecular absorption bands. Particles with CMC presented hydrodynamic radius between 4 and 102 nm and with PVA between 7 and 46 nm. The studied dispersions were toxic to A. salina species. Meyer's solution, used as dilution water in the test, caused precipitation of Ag⁺ and also caused changes in CMC-stabilized AgNPs, changing the shape of the nanoparticles by depositing precipitates on their surface. These changes make the results of toxicity difficult to interpret. AgNPs stabilized with PVA remained unchanged. AgNPs affected cell division and caused the appearance of chromosomal aberrations on A. cepa. Higher numbers of chromosomal aberrations occurred in dispersions with smaller particle diameters (AgNPs3-PVA and AgNPs5-PVA, without dilution). In the studied conditions the dispersions were toxic to the tested organisms, the concentrations of precursors and the type of stabilizer used influenced the particle size and toxicity. In the test with A. cepa, the reconstituted hard water did not cause changes in the dispersions of AgNPs, whereas for A. salina the Meyer solution promoted aggregation of the particles and precipitation, in the dispersions stabilized with CMC, thus changing the samples.

The antimicrobial efficacy of remote cold atmospheric plasma effluent against single and mixed bacterial biofilms of varying age

Cold atmospheric plasma (CAP) is a minimal food processing technology of increasing interest in the food industry, as it is mild in nature compared to traditional methods (e.g. pasteurisation) and thus can maintain the food's desirable qualities. However, due to this mild nature, the potential exists for post-treatment microbial survival and/or stress adaptation. Furthermore, biofilm inactivation by CAP is underexplored and mostly studied on specific foods or on plastic/polymer surfaces. Co-culture effects, biofilm age, and innate biofilm-associated resistance could all impact CAP efficacy, while studies on real foods are limited to the food product investigated without accounting for structural complexity. The effect of a Remote and Enclosed CAP device (Fourth State Medicine Ltd) was investigated on Escherichia coli and Listeria innocua grown as planktonic cells and as single or mixed bacterial biofilms of variable age, on a biphasic viscoelastic food model of controlled rheological and structural complexity. Post-CAP viability was assessed by plate counts, cell sublethal injury was quantified using flow cytometry, and biofilms were characterised and assessed using total protein content and microscopy techniques. A greater impact of CAP on planktonic cells was observed at higher air flow rates, where the ReCAP device operates in a mode more favourable to reactive oxygen species than reactive nitrogen species. Although planktonic E. coli was more susceptible to CAP than planktonic L. innocua, the opposite was observed in biofilm form. The efficacy of CAP was reduced with increasing biofilm age. Furthermore, E. coli produced much higher protein content in both single and mixed biofilms than L. innocua. Consequently, greater survival of L. innocua in mixed biofilms was attributed to a protective effect from E. coli. These results show that biofilm susceptibility to CAP is age and bacteria dependent, and that in mixed biofilms bacteria may become less susceptible to CAP. These findings are of significance to the food industry for the development of effective food decontamination methods using CAP.

Cadmium Selenide Formation Influences the Production and Characteristics of Extracellular Polymeric Substances of Anaerobic Granular Sludge

Feeding cadmium (II) and selenium (IV) simultaneously to anaerobic granular sludge with the aim of synthesizing cadmium selenide (CdSe) nanoparticles induces compositional changes in the extracellular polymeric substances (EPS) matrix of this sludge. A methanogenic anaerobic granular sludge was repeatedly exposed to Cd(II) (10-50 mg L^-1) and selenite (79 mg L^-1) for 300 days at pH 7.3 and 30 °C in a fed-batch feeding regime for enrichment of Se-reducing bacteria and synthesis of CdSe nanoparticles. EPS fingerprints of the granular sludge, obtained by size exclusion chromatography coupled to a fluorescence detector, showed a significant increase in the intensity of protein-like substances with > 100 kDa apparent molecular weight (aMW) upon repeated exposure to Cd(II) and Se(VI). This was accompanied by a prominent decrease in protein-like substances of aMW < 10 kDa. The fingerprint of the humic-like substances showed emergence of a new peak with aMW of 13 to 300 kDa in the EPS extracted from the Cd/Se fed granular sludge. Experiments on metal(loid)-EPS interactions showed that the CdSe nanoparticles interact mainly with loosely bound EPS (LB-EPS). This study showed that the formation of Se(0) and CdSe nanoparticles occurs in the LB-EPS fraction of the granular sludge and repeated exposure to Cd and Se induces compositional changes in the EPS matrix.

Biofilm Produced In Vitro by Piscirickettsia salmonis Generates Differential Cytotoxicity Levels and Expression Patterns of Immune Genes in the Atlantic Salmon Cell Line SHK-1

Piscirickettsia salmonis is the causative agent of Piscirickettsiosis, an infectious disease with a high economic impact on the Chilean salmonid aquaculture industry. This bacterium produces biofilm as a potential resistance and persistence strategy against stressful environmental stimuli. However, the in vitro culture conditions that modulate biofilm formation as well as the effect of sessile bacteria on virulence and immune gene expression in host cells have not been described for P. salmonis. Therefore, this study aimed to analyze the biofilm formation by P. salmonis isolates under several NaCl and iron concentrations and to evaluate the virulence of planktonic and sessile bacteria, together with the immune gene expression induced by these bacterial conditions in an Atlantic salmon macrophage cell line. Our results showed that NaCl and Fe significantly increased biofilm production in the LF-89 type strain and EM-90-like isolates. Additionally, the planktonic EM-90 isolate and sessile LF-89 generated the highest virulence levels, associated with differential expression of il-1β, il-8, nf-κb, and iκb-α genes in SHK-1 cells. These results suggest that there is no single virulence pattern or gene expression profile induced by the planktonic or sessile condition of P. salmonis, which are dependent on each strain and bacterial condition used.

Three-Dimensional In Vitro Staphylococcus aureus Abscess Communities Display Antibiotic Tolerance and Protection from Neutrophil Clearance

Staphylococcus aureus is a prominent human pathogen in bone and soft-tissue infections. Pathophysiology involves abscess formation, which consists of central staphylococcal abscess communities (SACs), surrounded by a fibrin pseudocapsule and infiltrating immune cells. Protection against the ingress of immune cells such as neutrophils, or tolerance to antibiotics, remains largely unknown for SACs and is limited by the lack of availability of in vitro models. We describe a three-dimensional in vitro model of SACs grown in a human plasma-supplemented collagen gel. The in vitro SACs reached their maximum size by 24 h and elaborated a fibrin pseudocapsule, as confirmed by electron and immunofluorescence microscopy. The in vitro SACs tolerated 100× the MIC of gentamicin alone and in combination with rifampin, while planktonic controls and mechanically dispersed SACs were efficiently killed. To simulate a host response, SACs were exposed to differentiated PLB-985 neutrophil-like (dPLB) cells and to primary human neutrophils at an early stage of SAC formation or after maturation at 24 h. Both cell types were unable to clear mature in vitro SACs, but dPLB cells prevented SAC growth upon early exposure before pseudocapsule maturation. Neutrophil exposure after plasmin pretreatment of the SACs resulted in a significant decrease in the number of bacteria within the SACs. The in vitro SAC model mimics key in vivo features, offers a new tool to study host-pathogen interactions and drug efficacy assessment, and has revealed the functionality of the S. aureus pseudocapsule in protecting the bacteria from host phagocytic responses and antibiotics.

Responses of freshwater biofilm formation processes (from colonization to maturity) to anatase and rutile TiO2 nanoparticles: Effects of nanoparticles aging and transformation

Most of the current studies on the toxicology of pristine nanoparticles (NPs) are environmentally irrelevant, because their ''aging'' process accompanied by the physicochemical transformation is inevitable in the environment. Considering aging phenomenon will gain a better understanding of the toxicity and fate of NPs in the environment. Here, we focused on the physicochemical transformation of anatase-NPs (TiO₂-A) and rutile-NPs (TiO₂-R) after 90 days of aging and investigated the responses of freshwater biofilm formation to the stress changes of naturally aged TiO₂-NPs (aTiO₂-NPs). We found that after aging, the TiO₂-NPs underwent sophisticated physicochemical transformations in the original morphology and microstructure owing to organic and crystal salts inclusions, such as energy band changes and the formation of Ti³⁺ on the NPs surfaces. These comprehensive transformations increased the stability of NPs in the exposed suspension. However, the physicochemical transformations were crystal-forms-dependent, and aging did not change the crystal structure and crystallinity. Interestingly, compared to pristine NPs, aTiO₂-NPs showed much lower cytotoxicity and had the weaker ability to promote or inhibit the biofilm formation (p < 0.05) owing to the passivation of photoactivity caused by the comprehensive effect of the inclusions, especially for aTiO₂-A. Regardless of aging or not of crystal forms, responses of biofilm formation were exposure-concentration-dependent, namely low concentration promotion (0.1 mg/L) and high concentration inhibition (10 mg/L), e.g., role transition of the pioneers (algae or bacteria) in initial colonization, extracellular polymeric substances (EPS) secretion and compositions of development stages with polysaccharide (PS)-rich and protein (PRO)-rich stages, and biomass and cell activity at different depths of mature biofilms. The reactive oxygen species (ROS) induced by TiO₂-NPs showed typical hormesis. The changing trends of the autoinducers (c-di-GMP and quorum sensing signals including AHL and AI-2) were highly consistent with the growth stages of biofilms and were stimulated or suppressed by TiO₂-NPs. The NPs crystal-dependently changed the microorganism community structures, while the UPGMA clustering of bacteria was based on the growth stages of the biofilms. The toxic mechanisms revealed that photoactivity and nanoscale retention of particles are the main reasons for the differences in the ecological stress capacity of four kinds of TiO₂-NPs. Aging reduced characteristic differences of two pristine NPs and even reversed their relative stresses levels (p > 0.05). However, the toxicity of high-concentration aTiO₂-NPs (10 mg/L) remained serious in a water environment. This study provides a better understanding for the water environmental risks evaluation and policy control of nanoparticles, that is, the effect of time aging has to be considered.

Biogenically Synthesized Polysaccharides-Capped Silver Nanoparticles: Immunomodulatory and Antibacterial Potentialities Against Resistant Pseudomonas aeruginosa

Bacterial infections are the key cause of death in patients suffering from burns and diabetic wounds while the use of traditional antibiotics has been growing steadily. Thus, in the present study, we are trying to introduce a paradigm shift strategy to improve chronic wound healing of bacterial infection. To that end, we have biologically synthesized silver nanoparticles (AgNPs) using Arthrospira sp polysaccharides, and evaluated their antibacterial efficacy with their safety pattern. Scanning electron micrographs showed spherical AgNPs coated with algal polysaccharides with an approximate size of 9.7 nm. Treatment of Pseudomonas aeruginosa with the AgNPs (0.5–1 μg/mL) resulted in a significant disruption in P. aeruginosa outer membrane, reduction in biofilm formation, and a significant decrease of production of alginate and pyocyanin along with a concentration-dependent reduction in β-lactamase activity. In addition, at the in vivo level, AgNPs displayed substantial activity to control P. aeruginosa infections in rat skin wounds with significant reduction in in COX-2 enzyme in both rat skin homogenate and serum samples. Furthermore, AgNPs facilitated wound curative in the P. aeruginosa infected model by reducing the hemorrhagic areas number and the infiltrated inflammatory cells. Taken all together, these biogenic nanoparticles showed unique properties in controlling bacterial wound infections and improving the healing process of damaged tissues via its direct and indirect effects.

Efficient removal of disinfection by-products precursors and inhibition of bacterial detachment by strong interaction of EPS with coconut shell activated carbon in ozone/biofiltration

The change of water quality was investigated in pilot-scale ozone-biological activated carbon (O₃-BAC) filters using an emerging coconut shell-based granular activated carbon (CAC) or traditional granular activated carbon (GAC), respectively. More dissolved organic carbon (DOC) and disinfection by-products (DBPs) precursors were removed, meanwhile, less microbes, less metabolites and smaller microbial clusters were detected in the effluent of CAC compared with GAC. Sequentially, lower DBPs formation and higher disinfection efficiency were achieved in drinking water distribution systems (DWDSs). Furthermore, it was observed that extracellular electron transfer was enhanced in the attached biofilms of CAC, hence improving the microbial metabolic activity and biological removal of DOC. The results were attributed to the strong interaction of extracellular polymeric substances (EPS) with highly graphitized CAC. In addition, CAC resulted in totally different EPS in attached biofilms with superior characteristics including stronger viscosity, higher flocculating efficiency, mechanical stability and numerous binding sites for bacterial cells. Consequently, a wide range of compact interconnected biofilms formed on the surface of CAC and exhibited certain binding effect for microbial flocs and metabolites. Therefore, CAC resulted in higher microbial metabolic activity and lower release of microbes and metabolites, which was beneficial to maintain water quality safety in downstream DWDSs.

Digital Proxy of a Bio-Reactor (DIYBOT) combines sensor data and data analytics to improve greywater treatment and wastewater management systems

Technologies to treat wastewater in decentralized systems are critical for sustainable development. Bioreactors are suitable for low-energy removal of inorganic and organic compounds, particularly for non-potable applications where a small footprint is required. One of the main problems associated with bioreactor use is sporadic spikes of chemical toxins, including nanoparticles. Here, we describe the development of DIYBOT (Digital Proxy of a Bio-Reactor), which enables remote monitoring of bioreactors and uses the data to inform decisions related to systems management. To test DIYBOT, a household-scale membrane aerated bioreactor with real-time water quality sensors was used to treat household greywater simulant. After reaching steady-state, silver nanoparticles (AgNP) representative of the mixture found in laundry wastewater were injected into the system to represent a chemical contamination. Measurements of carbon metabolism, effluent water quality, biofilm sloughing rate, and microbial diversity were characterized after nanoparticle exposure. Real-time sensor data were analyzed to reconstruct phase-space dynamics and extrapolate a phenomenological digital proxy to evaluate system performance. The management implication of the stable-focus dynamics, reconstructed from observed data, is that the bioreactor self-corrects in response to contamination spikes at AgNP levels below 2.0 mg/L. DIYBOT may help reduce the frequency of human-in-the-loop corrective management actions for wastewater processing.

Biofouling and me: My Stockholm syndrome with biofilms

Biofouling is the undesired deposition and growth of microorganisms on surfaces, forming biofilms. The definition is subjective and operational: not every biofilm causes biofouling - only if a given a subjective "threshold of interference" is exceeded, biofilms cause technical or medical problems. These range from the formation of slime layers on ship hulls or in pipelines, which increase friction resistance, to separation membranes, on which biofilms increase hydraulic resistance, to heat exchangers where they interfere with heat transport to contamination of treated water by eroded biofilm cells which may comprise hygienically relevant microorganisms, and, most dangerous, to biofilms on implants and catheters which can cause persistent infections. The largest fraction of anti-fouling research, usually in short-term experiments, is focused on prevention or limiting primary microbial adhesion. Intuitively, this appears only logical, but turns out mostly hopeless. This is because in technical systems with open access for microorganisms, all surfaces are colonized sooner or later which explains the very limited success of that research. As a result, the use of biocides remains the major tool to fight persistent biofilms. However, this is costly in terms of biocides, it stresses working materials, causes off-time and environmental damage and it usually leaves large parts of biofilms in place, ready for regrowth. In order to really solve biofouling problems, it is necessary to learn how to live with biofilms and mitigate their detrimental effects. This requires rather an integrated strategy than aiming to invent "one-shot" solutions. In this context, it helps to understand the biofilm way of life as a natural phenomenon. Biofilms are the oldest, most successful and most widely distributed form of life on earth, existing even in extreme environments and being highly resilient. Microorganisms in biofilms live in a self-produced matrix of extracellular polymeric substances (EPS) which allows them to develop emerging properties such as enhanced nutrient acquisition, synergistic microconsortia, enhanced tolerance to biocides and antibiotics, intense intercellular communication and cooperation. Transiently immobilized, biofilm organisms turn their matrix into an external digestion system by retaining complexed exoenzymes in the matrix. Biofilms grow even on traces of any biodegradable material, therefore, an effective anti-fouling strategy comprises to keep the system low in nutrients (good housekeeping), employing low-fouling, easy-to-clean surfaces, monitoring of biofilm development, allowing for early intervention, and acknowledging that cleaning can be more important than trying to kill biofilms, because cleaning does not cut the nutrient supply of survivors and dead biomass serves as an additional carbon source for "cannibalizing" survivors, supporting rapid after growth. An integrated concept is presented as the result of a long journey of the author through biofouling problems.

Towards a better understanding of Pseudomonas putida biofilm formation in the presence of ZnO nanoparticles (NPs): Role of NP concentration

Elucidating the effects of nanoparticles (NPs) on key bacterial functions not only deepens our understanding of nano-toxicity mechanisms, but also guides us in the design criteria for manufacturing safe nanomaterials. In this study, bacterial growth, biofilm development and the expression of biofilm-related genes were monitored in Pseudomonas putida KT2440, a plant-beneficial bacterium, following exposure to ZnO NPs. Low concentrations of NPs (0.5-30 mg L^-1) significantly promoted bacterial growth and biofilm formation, while higher concentrations (>30 mg L^-1) significantly inhibited biofilm formation. Confocal laser scanning microscopy revealed that microscope slides coated with 0.5 mg L^-1 of ZnO NPs showed enhanced bacterial colonization and biomass production, but at higher concentrations (250 mg L^-1), biomass production was about 11 times lower than that of the substrate without NPs. Increased protein and sugar contents of the biofilm matrix corroborated the stimulating effects of low concentrations of ZnO NPs. Physiological data were supported by changes in the expression of genes associated with oxidative stress and biofilm development. ZnO NPs at 0.5 mg L^-1 stimulated the expression of quorum sensing, lipopolysaccharide biosynthesis, and antibiotic resistance genes; high concentrations of ZnO NPs (250 mg L^-1) down-regulated biofilm formation-related genes and up-regulated antioxidant genes. Our results indicate that long-term release of low concentrations of ZnO NPs to the environment would promote undesired biofilm formation and increased resistance to antibiotics.

Biosynthesis of silver nanoparticles by Fusarium scirpi and its potential as antimicrobial agent against uropathogenic Escherichia coli biofilms

The ability of Uropathogenic Escherichia coli (UPEC) to form biofilms, can be considered an important factor that contributes to the prevalence of Urinary Tract Infections (UTIs) due to the inaccessibility of the antibiotics into the highly complex structure of the biofilm. Moreover, with the appearance of antibiotic multiresistant UPEC strains, the alternatives of treatment of UTIs are less. Silver nanoparticles (AgNPs) can be useful in the treatment of the UPEC infections due to its physicochemical properties that confer them antibacterial activity against both planktonic and biofilm structured cells. A diversity of biological methods for synthesis of AgNPs with antimicrobial activity has been widely investigated during the last decades, between these methods; the fungal-biosynthesis of AgNPs highlights as an ecofriendly, scalable and low cost method. In this study, biogenic AgNPs were synthesized with extracellular metabolites secreted by the soil fungal strain Fusarium scirpi (Ag0.5–5) by an ecofriendly, simple and efficient method. The antimicrobial activity of the biosynthesized AgNPs against UPEC was evaluated. The Minimal Inhibitory Concentration (MIC) of biogenic AgNPs over planktonic UPEC cells was 25 mg/mL, whereas a sub-MIC concentration (7.5 mg/L) was sufficient to inhibit the UPEC-biofilm formation about a 97%, or produce the disruption of an 80% of mature UPEC-biofilms demonstrating the potential of fungal-derived AgNPs to prevent UPEC infections.

Antimicrobial Silver Nanoparticles for Wound Healing Application: Progress and Future Trends

Recent data have reported that the burden of infections related to antibiotic-resistant bacteria in the European Union and European Economic Area (EEA) can be estimated as the cumulative burden of tuberculosis, influenza, and human immunodeficiency virus (HIV). In wound management, the control of infections represents a crucial issue and a multi-billion dollar industry worldwide. For diabetic wounds ulcers, in particular, infections are related to the majority of amputations in diabetic patients, which today represent an increasing number of the elderly. The greatest barrier to healing is represented by the biofilm, an organized consortium of bacteria encapsulated in a self-produced extracellular polymeric substance with high resistance to conventional antimicrobial therapies. There is an urgent need for novel anti-biofilm strategies and novel antimicrobial agents and, in this scenario, silver nanotechnology has received tremendous attention in recent years in therapeutically enhanced healthcare. Due to its intrinsic therapeutic properties and the broad-spectrum antimicrobial efficacy, silver nanoparticles have opened new horizons towards novel approaches in the control of infections in wound healing. This review aims at providing the reader with an overview of the most recent progress in silver nanotechnology, with a special focus on the role of silver in the wound healing process.

Antibacterial effect of graphene oxide (GO) nano-particles against Pseudomonas putida biofilm of variable age

Graphene oxide (GO) has been reported to possess antibacterial activity; therefore, its accumulation in the environment could affect microbial communities such as biofilms. The susceptibility of biofilms to antimicrobials is known to depend on the stage of biofilm maturity. The aim of this study was to investigate the effect of GO nano-particles on Pseudomonas putida KT2440 biofilm of variable age. FT-IR, UV-vis, and Raman spectroscopy confirmed the oxidation of graphene while XPS confirmed the high purity of the synthesised GO over 6 months. Biofilms varying in maturity (24, 48, and 72 h) were formed using a CDC reactor and were treated with GO (85 μg/mL or 8.5 μg/mL). The viability of P. putida was monitored by culture on media and the bacterial membrane integrity was assessed using flow cytometry. P. putida cells were observed using confocal microscopy and SEM. The results showed that GO significantly reduced the viability of 48-h biofilm and detached biofilm cells associated with membrane damage while the viability was not affected in 24- and 72-h biofilms and detached biofilm cells. The results showed that susceptibility of P. putida biofilm to GO varied according to age which may be due to changes in the physiological state of cells during maturation. Graphical abstract.

Down-regulatory effects of green coffee extract on las I and las R virulence-associated genes in Pseudomonas aeruginosa

BACKGROUND

Antibiotic resistant strains of Pseudomonas aeruginosa are the cause of Gram negative nosocomial infections especially among the immunosuppressed patients. The bacteria contains las I and las R genes that play very important roles in the pathogenesis and mechanisms of aggression. These genes can be influenced by the quorum sensing (QS) system and such mechanism is becoming clinically important worldwide. This study aimed to investigate the preventive effects of green coffee extract (GCE) on the expression of pathogenesis-related genes, las I and las R in P. aeruginosa.

METHODS

A total of fifty four P. aeruginosa strains were isolated out of 100 clinical samples collected from the infectious wards in different hospitals (Tehran province) using conventional microscopic and biochemical methods. Susceptibility of the isolates to different antibiotics, GCE and chlorogenic acid were elucidated. Multiplex polymerase chain reaction (PCR) and real-time PCR were performed to detect and quantify the expression levels of las I and las R genes. The presence of chlorogenic acid in GCE was confirmed by HPLC.

RESULTS

Antibiotic susceptibility tests revealed multidrug resistance among the clinical isolates of those 40 strains were resistant to ciprofloxacin (74.07%), 43 to ceftazidime (79.26%), 29 to amikacin (53.7%), 42 to ampicillin (77.77%), 17 to colistin (31.48%), 40 to gentamicin (74.77%), and 50 to piperacillin (92.59%). PCR outcomes exhibited that the frequency of las I and las R genes were 100% in resistant and sensitive strains isolated from clinical and standard strains of P. aeruginosa (ATCC 15449). Real-time PCR analyses revealed that GCE significantly prevented the expression of las I and las R genes in P. aeruginosa. GCE at concentration level as low as 2.5 mg/mL could prevent the expression of lasI and lasR genes in P. aeruginosa clinical isolates.

CONCLUSION

The presence and expression levels of las I and las R genes in P. aeruginosa isolates were investigated when the bacteria was exposed to GCE. Our results tend to suggest that genes involved in pathogenesis of:Pseudomonas aeruginosa are down regulated by quorum sensing effect of chlorogenic acid and therefore GCE could be useful as an adjuvant in combating multidrug resistance strains of Pseudomonas aeruginosa.

Silver nanoparticles exert concentration-dependent influences on biofilm development and architecture

Objectives

To investigate the impact of silver nanoparticles (AgNPs) on the biofilm growth and architecture.

Materials and methods

Silver nitrate was reduced by d‐maltose to prepare AgNPs in the presence of ammonia and sodium hydroxide. The physicochemical properties of AgNPs were characterized by transmission electron microscopy, ultraviolet‐visible spectroscopy and inductively coupled plasma mass spectrometry. The development of biofilm with and without AgNPs was explored by crystal violet stain. The structures of mature biofilm were visually studied by confocal laser scanning microscopy and scanning electron microscopy. Bacterial cell, polysaccharide and protein within biofilm were assessed quantitatively by colony‐counting method, phenol‐sulphuric acid method and Bradford assay, respectively.

Results

The spherical AgNPs (about 30 nm) were successfully synthesized. The effect of AgNPs on Pseudomonas aeruginosa biofilm development was concentration‐dependent. Biofilm was more resistant to AgNPs than planktonic cells. Low doses of AgNPs exposure remarkably delayed the growth cycle of biofilm, whereas high concentration (18 μg/mL) of AgNPs fully prevented biofilm development. The analysis of biofilm architecture at the mature stage demonstrated that AgNPs exposure at all concentration led to significant decrease of cell viability within treated biofilms. However, sublethal doses of AgNPs increased the production of both polysaccharide and protein compared to control, which significantly changed the biofilm structure.

Conclusions

AgNPs exert concentration‐dependent influences on biofilm development and structure, which provides new insight into the role of concentration played in the interaction between antibacterial nanoparticles and biofilm, especially, an ignored sublethal concentration associated with potential unintended consequences.

Low concentrations of copper oxide nanoparticles alter microbial community structure and function of sediment biofilms

In this study, we investigated the effects of copper oxide (CuO) NPs on freshwater sediment biofilms in terms of the functional properties and microbial community structure. Biofilms were incubated in microcosms and CuO NPs (1 mg/L uncoated and humic-acid-coated) were exposed with Cu²⁺ (Cu(NO₃)₂) as the positive control. As determined from DO (dissolved oxygen) microelectrodes measurements, a high-DO region emerged inside the biofilms after 5-day exposure to CuO NPs compared with those before NP additions, which suggested CuO NPs inhibit the oxygen respiration activity. These results were consistent with the decreased heterotrophic respiration. CuO NPs significantly altered the bacterial community composition and decreased the abundances of Anaerolineaceae, Acidobacteria, Aminicenantes, and Anaerolinea. Functional analysis from PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States)-predicted metagenomes indicated that bacterial genera depleted by CuO NP treatments were related to carbohydrate and glycan biosynthesis and metabolism, and biosynthesis of other secondary metabolites. These functional profiles combined with the decreased activities of extracellular enzymes, β-glucosidase (GLU) and l-leucine aminopeptidase (LAP), suggested that the introduction of CuO NPs exhibit negative effects on the biogeochemical processes and the cycling of carbon and nitrogen in biofilm systems. Whereas these toxic effects of CuO NPs could be mitigated when the aquatic environment is enriched with natural organic matters such as humic acid.

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.

Understanding Biofilms and Novel Approaches to the Diagnosis, Prevention, and Treatment of Medical Device-Associated Infections

Treatment of medical device-related infections is challenging and recurrence is common. The main reason for this is that microorganisms adhere to the surfaces of medical devices and enter into a biofilm state in which they display distinct growth rates, structural features, and protection from antimicrobial agents and host immune mechanisms compared with their planktonic counterparts. This article reviews how microorganisms form biofilms and the mechanisms of protection against antimicrobial agents and the host immune system provided by biofilms. Also discussed are innovative strategies for the diagnosis of biofilm-associated infection and novel approaches to treatment and prevention of medical device-associated infections.

Superior Bactericidal Efficacy of Fucose-Functionalized Silver Nanoparticles against Pseudomonas aeruginosa PAO1 and Prevention of Its Colonization on Urinary Catheters

Pseudomonas aeruginosa, a Gram-negative rod-shaped bacterium is a notorious pathogen causing chronic infections. Its ability to form antibiotic-resistant biofilm has raised the need for the development of alternative treatment approaches. An ideal alternate can be silver nanoparticles known for their strong yet tunable bactericidal activity. However, their use in commercial in vivo medicine could not see the light of the day because of the unwanted toxicity of silver in the host cells at higher concentrations. Thus, strategies which can modulate the bacterial cell-silver nanoparticle interactions thereby reducing the amount of nanoparticles required to kill a typical number of bacterial cells are utmost welcomed. The current work showcases one such strategy by functionalizing the silver nanoparticles with l-fucose to increase their interactions with the LecB lectins present on P. aeruginosa PAO1. The advantage of this approach lies in the higher bactericidal and antibiofilm activity of fucose-functionalized silver nanoparticles (FNPs) as compared to the citrate-capped silver nanoparticles (CNPs) of similar size and concentrations. The superior bactericidal potential of FNPs as demonstrated by fluorescence-assisted cell sorting, confocal laser scanning microscopy, and transmission electron microscopy analyses may be attributed to the higher reactive oxygen species generation and oxidative membrane damage. Additionally, FNPs prevented the formation of biofilms by downregulating the expression of various virulence genes at lower concentrations as compared to CNPs. The practical applicability of the approach was demonstrated by preventing bacterial colonization on artificial silicone rubber surfaces. These results can be extrapolated in the treatment of catheter-associated urinary tract infections caused by P. aeruginosa. In conclusion, the present work strongly advocates the use of antivirulence targets and their corresponding binding residues for the augmentation of the bactericidal effect of silver nanoparticles.

Myroides odoratimimus Forms Structurally Complex and Inherently Antibiotic-Resistant Biofilm in a Wound-Like in vitro Model

Myroides odoratimimus is an aerobic, non-fermenting Gram-negative multidrug-resistant bacterium widely distributed in nature that rarely causes infections in immunocompromised patients. We recently described in a diabetic patient a case of recurrent calcaneal ulcer infection caused by a M. odoratimimus strain showing potential for biofilm formation. For the first time, we therefore evaluated the ability of M. odoratimimus to form biofilm under different pH values and glucose concentrations using an in vitro “skin-like” model, and its susceptibility to levofloxacin, meropenem, and tigecycline. The expression of some antibiotic-resistance related genes was also monitored by RT-PCR during planktonic-to-biofilm transition. Our results indicated that M. odoratimimus can produce relevant amounts of biofilm biomass, in a time-dependent manner, especially at acidic pH and regardless of glucose concentration tested. The comparative analysis of MIC and MBC values between planktonic and sessile cells showed that resistance to antibiotics increased during the planktonic-to-biofilm transition. Viable cell count indicated that none of the tested antibiotics were able to completely eradicate preformed biofilms, although meropenem and levofloxacin were the most active causing a significant, dose-independent, reduction of biofilm's viability, as also confirmed by microscopic analysis. RT-PCR showed that antibiotic-resistance related gyrA and acrB genes are over-expressed during the transition from planktonic to sessile (biofilm) lifestyle. Overall, our findings showed that M. odoratimimus can form relevant amounts of inherently antibiotic-resistant biofilm under conditions relevant to wound site, therefore suggesting a role in the pathogenesis of chronic ulcer infections.

Effects of humic acid on the interactions between zinc oxide nanoparticles and bacterial biofilms

The effects of humic acid (HA) on interactions between ZnO nanoparticles (ZnO NPs) and Pseudomonas putida KT2440 biofilms at different maturity stages were investigated. Three stages of biofilm development were identified according to bacterial adenosine triphosphate (ATP) activity associated with biofilm development process. In the initial biofilm stage 1, the ATP content of bacteria was reduced by more than 90% when biofilms were exposed to ZnO NPs. However, in the mature biofilm stages 2 and 3, the ATP content was only slightly decreased. Biofilms at stage 3 exhibited less susceptibility to ZnO NPs than biofilms at stage 2. These results suggest that more mature biofilms have a significantly higher tolerance to ZnO NPs compared to young biofilms. In addition, biofilms with intact extracellular polymeric substances (EPS) showed higher tolerance to ZnO NPs than those without EPS, indicating that EPS play a key role in alleviating the toxic effects of ZnO NPs. In both pure ZnO NPs and ZnO-HA mixtures, dissolved Zn²⁺ originating from the NPs significantly contributed to the overall toxicity. The presence of HA dramatically decreased the toxicity of ZnO NPs due to the binding of Zn²⁺ on HA. The combined results from this work suggest that the biofilm maturity stages and environmental constituents (such as humic acid) are important factors to consider when evaluating potential risks of NPs to ecological systems.

Dependence of toxicity of silver nanoparticles on Pseudomonas putida biofilm structure

Susceptibility of biofilms with different physical structures to silver nanoparticles (AgNPs) was studied. Biofilms of Pseudomonas putida KT2440 were formed in batch conditions under different carbon sources (glucose, glutamic acid, and citrate), glucose concentrations (5 and 50 mM), and incubation temperatures (25 and 30 °C). The biofilms were observed using confocal laser scanning microscopy for their physical characteristics (biomass amount, thickness, biomass volume, surface to volume ratio, and roughness coefficient). The biofilms forming under different growth conditions exhibited different physical structures. The biofilm thickness and the roughness coefficient were found negatively and positively correlated with the biofilm susceptibility to AgNPs, respectively. The effect of AgNPs on biofilms was low (1-log reduction of cell number) when the biofilms had high biomass amount, high thickness, high biomass volume, low surface to volume ratio, and low roughness coefficient. Furthermore, the extracellular polymeric substance (EPS) stripping process was applied to confirm the dependence of susceptibility to AgNPs on the structure of biofilm. After the EPS stripping process, the biofilms forming under different conditions showed reduction in thickness and biomass volume, and increases in surface to volume ratio and roughness coefficient, which led to more biofilm susceptibility to AgNPs. The results of this study suggest that controlling the growth conditions to alter the biofilm physical structure is a possible approach to reduce the impact of AgNPs on biofilms in engineered and natural systems.

NanoEHS beyond Toxicity - Focusing on Biocorona

The first phase of environmental health and safety of nanomaterials (nanoEHS) studies has been mainly focused on evidence-based investigations that probe the impact of nanoparticles, nanomaterials and nano-enabled products on biological and ecological systems. The integration of multiple disciplines, including colloidal science, nanomaterial science, chemistry, toxicology/immunology and environmental science, is necessary to understand the implications of nanotechnology for both human health and the environment. While strides have been made in connecting the physicochemical properties of nanomaterials with their hazard potential in tiered models, fundamental understanding of nano-biomolecular interactions and their implications for nanoEHS is largely absent from the literature. Research on nano-biomolecular interactions within the context of natural systems not only provides important clues for deciphering nanotoxicity and nanoparticle-induced pathology, but also presents vast new opportunities for screening beneficial material properties and designing greener products from bottom up. This review highlights new opportunities concerning nano-biomolecular interactions beyond the scope of toxicity.

Biofilms: an emergent form of bacterial life

Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Lessons learned from more than two decades of research on emerging contaminants in the environment

In the last twenty years, thousands of research papers covering different aspects of emerging contaminants have been published, ranging from environmental occurrence to treatment and ecological effects. Emerging contaminants are environmental pollutants that have been investigated widely only in the last two decades and include anthropogenic and naturally occurring chemicals such as pharmaceuticals and personal care products and their metabolites, illicit drugs, engineered nanomaterials, and antibiotic resistance genes. The advancement in our knowledge on emerging contaminants has been the result of the appearance of highly sensitive and powerful analytical instrumentation that rapidly developed, allowing identification and trace quantification of unknown contaminants in complex environmental matrices. High efficiency chromatographic separations coupled to high-resolution mass spectrometers have become more common in environmental laboratories and are the pillars of environmental research, increasing our awareness and understanding of the presence of emerging contaminants in the environment, their transformation and fate, and the complex ecological consequences that they pose on exposed biological systems. This introductory paper for the Virtual Thematic Issue on Emerging Contaminants presents a brief literature overview on key research milestones in the area of emerging contaminants, focusing on pharmaceuticals and personal care products and endocrine disrupting compounds, and highlighting selected research papers previously published in the Journal of Hazardous Materials during the period of January 2012 to December 2015.

Biofilms Versus Activated Sludge: Considerations in Metal and Metal Oxide Nanoparticle Removal from Wastewater

The increasing application of metal and metal oxide nanoparticles [Me(O)NPs] in consumer products has led to a growth in concentration of these nanoparticles in wastewater as emerging contaminants. This may pose a threat to ecological communities (e.g., biological nutrient removal units) within treatment plants and those subject to wastewater effluents. Here, the toxicity, fate, and process implications of Me(O)NPs within wastewater treatment, specifically during activated sludge processing and biofilm systems are reviewed and compared. Research showed activated sludge achieves high removal rate of Me(O)NPs by the formation of aggregates through adsorption. However, recent literature reveals evidence that inhibition is likely for nutrient removal capabilities such as nitrification. Biofilm systems were much less studied, but show potential to resist Me(O)NP inhibition and achieve removal through possible retention by sorption. Implicating factors during bacteria-Me(O)NP interactions such as aggregation, surface functionalization, and the presence of organics are summarized. At current modeled levels, neither activated sludge nor biofilm systems can achieve complete removal of Me(O)NPs, thus allowing for long-term environmental exposure of diverse biological communities to Me(O)NPs in streams receiving wastewater effluents. Future research directions are identified throughout in order to minimize the impact of these nanoparticles released.

In vitro microbicidal, anti-biofilm and cytotoxic effects of different commercial antiseptics

Topical antiseptics are widely used for wound treatment, with the goal of disrupting biofilm capacity. We analysed the effectiveness of a variety of antiseptics to inhibit various stages of biofilm formation and to remove biofilms in vitro as well as the agents' cytotoxic effects on fibroblasts. We found that the chlorine-releasing agents exhibited immediate anti-biofilm effects in the short term, with lesser cytotoxicity than agents prepared from more stable compounds, such as biguanide or modified diallyl disulfide-oxide, which, conversely, have better long-term effectiveness. Among the examined organisms, Gram-positive bacteria and Candida albicans were the most sensitive to the antiseptics, whereas Pseudomonas aeruginosa and Acinetobacter baumannii were relatively resistant to them. Formulations whose mechanisms of action involve the release of chemically active chlorine were more effective when administered in solution than the gel form, likely because of the stability of the active ingredients during or after preparation of the formula. Interestingly, hypochlorous acid and some superoxidation solutions were effective in preventing biofilm formation within a short time period and showed virtually no toxicity. Our study indicates that most antiseptics remain effective long enough to prevent biofilm formation; thus, even brief application of an antiseptic agent during initial wound treatment can lead to better wound management outcomes.

Yeast-derived biosynthesis of silver/silver chloride nanoparticles and their antiproliferative activity against bacteria

Here, we provided the first evidence of Ag/AgCl-nanoparticles production in yeast strains fromin vitrocultures.