Nanoparticle–Biofilm Interactions: The Role of the EPS Matrix

Biofilm-overproducing Bacillus subtilis B12ΔYwcc decreases Cd uptake in Chinese cabbage through increasing Cd-immobilizing related gene abundance and root surface colonization

Biofilm-producing bacteria can decrease Cd uptake in vegetables, but mechanisms underlying this effect are poorly characterized. In this study, two mutant strains B12ΔYwcc and B12ΔSlrR were constructed from a biofilm-producing Bacillus subtilis strain B12. Then, the impacts of strain B12 and its high biofilm-producing mutant strain B12ΔYwcc and low biofilm-producing mutant strain B12ΔSlrR on Cd availability and uptake in Chinese cabbage and the related mechanisms were investigated in the Cd-polluted soil. Strain B12 and its mutants B12ΔYwcc and B12ΔSlrR increased the dry biomasses of edible tissues by 54%-130% compared with the controls. Strain B12 and its mutant B12ΔYwcc reduced the soil available Cd content by 36%-50% and root and edible tissue Cd contents by 23%-50% compared with the controls. Furthermore, the mutant strain B12ΔYwcc reduced the edible tissue Cd content by 40% and increased the polysaccharide content by 23%, invertase activity by 139%, and gene copies of the cumA by 4.5-fold, epsA by 7.1-fold, and cadA by 4.3-fold, which were involved in Cd adsorption in the rhizosphere soils, respectively, compared with strain B12. The polysaccharide content and cumA, epsA, and cadA gene copy numbers showed significantly reverse correlations with the available Cd content. Notably, the mutant strain B12ΔYwcc showed better ability to colonize the vegetable root surface than strain B12. These findings demonstrated that the biofilm-overproducing mutant strain B12ΔYwcc increased the polysaccharide production and Cd-immobilizing related cumA, epsA, and cadA gene copies, resulting in lower Cd availability and accumulation in Chinese cabbage in the Cd-polluted soil.

Microplastisphere may induce the enrichment of antibiotic resistance genes on microplastics in aquatic environments: A review

Microplastics have been proven to be hotspots of bacterial pathogens and antibiotic resistance genes (ARGs). The enrichment of ARGs in microplastisphere, the specific niche for diverse microbial communities attached to the surface of microplastic, has attracted worldwide attention. By collecting 477 pairs of ARG abundance data belonging to 26 ARG types, based on the standardized mean difference (SMD) under the random effect model, we have performed the first meta-analysis of the ARG enrichment on microplastics in aquatic environments in order to quantitatively elucidate the enrichment effect, with comparison of non-microplastic materials. It was found that ARGs enriched on the microplastics were more abundant than that on the inorganic substrates (SMD = 0.26) and natural water environments (SMD = 0.10), but lower abundant than that on the natural organic substrates (SMD = -0.52). Furthermore, microplastics in freshwater tended to have a higher degree of ARG enrichment than those in saline water and sewage. The biofilm formation stage, structure, and component of microplastisphere may play a significant role in the enrichment of ARGs.

Novel Antibacterial, Cytotoxic and Catalytic Activities of Silver Nanoparticles Synthesized from Acidophilic Actinobacterial SL19 with Evidence for Protein as Coating Biomolecule

Silver nanoparticles (AgNPs) have potential applications in medicine, photocatalysis, agriculture, and cosmetic fields due to their unique physicochemical properties and strong antimicrobial activity. Here, AgNPs were synthesized using actinobacterial SL19 strain, isolated from acidic forest soil in Poland, and confirmed by UV-vis and FTIR spectroscopy, TEM, and zeta potential analysis. The AgNPs were polydispersed, stable, spherical, and small, with an average size of 23 nm. The FTIR study revealed the presence of bonds characteristic of proteins that cover nanoparticles. These proteins were then studied by using liquid chromatography with tandem mass spectrometry (LC-MS/ MS) and identified with the highest similarity to hypothetical protein and porin with molecular masses equal to 41 and 38 kDa, respectively. Our AgNPs exhibited remarkable antibacterial activity against Escherichia coli and Pseudomonas aeruginosa. The combined, synergistic action of these synthesized AgNPs with commercial antibiotics (ampicillin, kanamycin, streptomycin, and tetracycline) enabled dose reductions in both components and increased their antimicrobial efficacy, especially in the case of streptomycin and tetracycline. Furthermore, the in vitro activity of the AgNPs on human cancer cell lines (MCF-7, A375, A549, and HepG2) showed cancer-specific sensitivity, while the genotoxic activity was evaluated by Ames assay, which revealed a lack of mutagenicity on the part of nanoparticles in Salmonella Typhimurium TA98 strain. We also studied the impact of the AgNPs on the catalytic and photocatalytic degradation of methyl orange (MO). The decomposition of MO was observed by a decrease in intensity of absorbance within time. The results of our study proved the easy, fast, and efficient synthesis of AgNPs using acidophilic actinomycete SL19 strain and demonstrated the remarkable potential of these AgNPs as anticancer and antibacterial agents. However, the properties and activity of such particles can vary by biosynthesized batch.

Periphytic biofilms-mediated microbial interactions and their impact on the nitrogen cycle in rice paddies

Rice paddies are unique waterlogged wetlands artificially constructed for agricultural production. Periphytic biofilms (PBs) at the soil-water interface play an important role in rice paddies characterized by high nutrient input but low utilization efficiency. PBs are composed of microbial aggregates, including a wide variety of microorganisms (algae, bacteria, fungi, protozoa, and metazoa), extracellular polymeric substances and minerals (iron, aluminum, and calcium), which form an integrated food web and energy flux within a relatively stable micro-ecosystem. PBs are crucial to regulate and streamline the nitrogen cycle by neutralizing nitrogen losses and improving rice production since PBs can serve as both a sink by capturing surplus nitrogen and a source by slowly re-releasing this nitrogen for reutilization. Here the ecological advantages of PBs in regulating the nitrogen cycle in rice paddies are illustrated. We summarize the key functional importance of PBs, including the intricate and delicate community structure, microbial interactions among individual phylotypes, a wide diversity of self-produced organics, the active adaptation of PBs to constantly changing environments, and the intricate mechanisms by which PBs regulate the nitrogen cycle. We also identify the future challenges of microbial interspecific cooperation in PBs and their quantitative contributions to agricultural sustainability, optimizing nitrogen utilization and crop yields in rice paddies.

Detection and various environmental factors of antibiotic resistance gene horizontal transfer

Bacterial antibiotic resistance in water environments is becoming increasingly severe, and new antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have also attracted the attention of researchers. The horizontal transfer of ARGs in water environments is considered one of the main sources of bacterial resistance in the natural environment. Horizontal gene transfer (HGT) mainly includes conjugation, natural transformation, and transduction, and conjugation has been investigated most. Several studies have shown that there are a large number of environmental factors that might affect the horizontal transfer of ARGs in water environments, such as nanomaterials, various oxidants, and light; however, there is still a lack of systematic and comprehensive reviews on the detection and the effects of the influence factors of on ARG horizontal transfer. Therefore, this study introduced three HGT modes, analysed the advantages and disadvantages of current methods for monitoring HGT, and then summarized the influence and mechanism of various factors on ARG horizontal transfer, and the possible reasons for the different effects caused by similar factors were mainly critically discussed. Finally, existing research deficiencies and future research directions of ARG horizontal transfer in water environments were discussed.

Polydopamine-Based Nanoparticles for an Antibiofilm Platform: Influence of Size and Surface Charge on Their Penetration and Accumulation in S. aureus Biofilms

Various functional polydopamine (PDA) nanoparticles have been developed to treat biofilms in recent years; however, in-depth knowledge of how the physicochemical properties of the nanoparticles impact their penetration and accumulation in biofilms is lacking. In this work, PDA nanoparticles of 15, 60, 90, and 200 nm sizes were synthesized and carboxyl, methoxy, and amine groups were introduced to the particle surface to control their surface charges, and then the penetration and accumulation of these PDA nanoparticles in S. aureus biofilms were investigated. The PDA nanoparticles of approximately 60 nm size (PDA60) showed higher penetration and accumulation abilities than nanoparticles of other sizes, and the positively charged amine groups introduced onto the surfaces of PDA60 nanoparticles were more effective than carboxyl or methoxy groups in promoting the interactions of the nanoparticles with the biofilm. The PDA60 nanoparticles with amine surface groups exhibited good photothermal properties, and confocal laser scanning microscopy revealed that they were able to accumulate in the biofilm in significant amounts, which upon irradiation with a laser of 808 nm wavelength showed a high bactericidal rate (97.1%) against the biofilm. The findings of this work provide guidance for the design and development of nanoparticles for antibiofilm application.

Poly-(lactic-co-glycolic) Acid Nanoparticles Entrapping Pterostilbene for Targeting Aspergillus Section Nigri

Poly-(lactic-co-glycolic) acid (PLGA) is a biodegradable, biosafe, and biocompatible copolymer. The Aspergillus section Nigri causes otomycosis localized in the external auditory canal. In this research, Aspergillus brasiliensis, a species belonging to the Nigri section, was tested. Coumarin 6 and pterostilbene loaded in poly-(lactic-co-glycolic) acid nanoparticles (PLGA-coumarin6-NPs and PLGA-PTB-NPs) were tested for fungal cell uptake and antifungal ability against A. brasiliensis biofilm, respectively. Moreover, the activity of PLGA-PTB-NPs in inhibiting the A. brasiliensis infection was tested using Galleria mellonella larvae. The results showed a fluorescence signal, after 50 nm PLGA-coumarin6-NPs treatment, inside A. brasiliensis hyphae and along the entire thickness of the biofilm matrix, which was indicative of an efficient NP uptake. Regarding antifungal activity, a reduction in A. brasiliensis biofilm formation and mature biofilm with PLGA-PTB-NPs has been demonstrated. Moreover, in vivo experiments showed a significant reduction in mortality of infected larvae after injection of PLGA-PTB-NPs compared to free PTB at the same concentration. In conclusion, the PLGA-NPs system can increase the bioavailability of PTB in Aspergillus section Nigri biofilm by overcoming the biofilm matrix barrier and delivering PTB to fungal cells.

Inhibitory Effect of Epigallocatechin Gallate-Silver Nanoparticles and Their Lysozyme Bioconjugates on Biofilm Formation and Cytotoxicity

Biofilms are multicellular communities of microbial cells that grow on natural and synthetic surfaces. They have become the major cause for hospital-acquired infections because once they form, they are very difficult to eradicate. Nanotechnology offers means to fight biofilm-associated infections. Here, we report on the synthesis of silver nanoparticles (AgNPs) with the antibacterial ligand epigallocatechin gallate (EGCG) and the formation of a lysozyme protein corona on AgNPs, as shown by UV-vis, dynamic light scattering, and circular dichroism analyses. We further tested the activity of EGCG-AgNPs and their lysozyme bioconjugates on the viability of Bacillus subtilis cells and biofilm formation. Our results showed that, although EGCG-AgNPs presented no antibacterial activity on planktonic B. subtilis cells, they inhibited B. subtilis biofilm formation at concentrations larger than 40 nM, and EGCG-AgNP-lysozyme bioconjugates inhibited biofilms at concentrations above 80 nM. Cytotoxicity assays performed with human cells showed a reverse trend, where EGCG-AgNPs barely affected human cell viability while EGCG-AgNP-lysozyme bioconjugates severely hampered viability. Our results therefore demonstrate that EGCG-AgNPs may be used as noncytotoxic antibiofilm agents.

Interaction between Engineered Pluronic Silica Nanoparticles and Bacterial Biofilms: Elucidating the Role of Nanoparticle Surface Chemistry and EPS Matrix

Nanoparticles (NPs) are considered a promising tool in the context of biofilm control. Many studies have shown that different types of NPs can interfere with the bacterial metabolism and cellular membranes, thus making them potential antibacterial agents; however, fundamental understanding is still lacking on the exact mechanisms involved in these actions. The development of NP-based approaches for effective biofilm control also requires a thorough understanding of how the chosen nanoparticles will interact with the biofilm itself, and in particular with the biofilm self-produced extracellular polymeric matrix (EPS). This work aims to provide advances in the understanding of the interaction between engineered fluorescent pluronic silica (PluS) nanoparticles and bacterial biofilms, with a main focus on the role of the EPS matrix in the accumulation and diffusion of the particles in the biofilm. It is demonstrated that particle surface chemistry has a key role in the different lateral distribution and specific affinity to the biofilm matrix components. The results presented in this study contribute to our understanding of biofilm-NP interactions and promote the principle of the rational design of smart nanoparticles as an important tool for antibiofilm technology.

Self-locomotive, antimicrobial microrobot (SLAM) swarm for enhanced biofilm elimination

Biofilm is a major cause of infections and infrastructure deterioration, largely due to molecular diffusion restrictions that hamper the antimicrobial activity of traditional antibiotics and disinfectants. Here, we present a self-locomotive, antimicrobial microrobot (SLAM) swarm that can penetrate, fracture, and detach biofilm and, in turn, nullify bacterial resistance to antibiotics. The SLAM is assembled by loading a controlled mass of manganese oxide nanosheets on diatoms with the polydopamine binder. In hydrogen peroxide solution, SLAMs produce oxygen bubbles that generate thrust to penetrate the rigid and dense Pseudomonas aeruginosa biofilm and self-assemble into a swarm that repeatedly surrounds, expands, and bursts oxygen bubbles. The resulting cavities continue to deform and fracture extracellular polymeric substances from microgrooved silicone substrates and wounded skin explants while decreasing the number of viable bacterial cells. Additionally, SLAM allows irrigating water or antibiotics to access the residual biofilm better, thus enhancing the synergistic efficacy in killing up to 99.9% of bacterial cells.

Predicted Adsorption Affinity for Enteric Microbial Metabolites to Metal and Carbon Nanomaterials

Ingested nanomaterials are exposed to many metabolites that are produced, modified, or regulated by members of the enteric microbiota. The adsorption of these metabolites potentially affects the identity, fate, and biodistribution of nanomaterials passing the gastrointestinal tract. Here, we explore these interactions using in silico methods, focusing on a concise overview of 170 unique enteric microbial metabolites which we compiled from the literature. First, we construct quantitative structure–activity relationship (QSAR) models to predict their adsorption affinity to 13 metal nanomaterials, 5 carbon nanotubes, and 1 fullerene. The models could be applied to predict log k values for 60 metabolites and were particularly applicable to ‘phenolic, benzoyl and phenyl derivatives’, ‘tryptophan precursors and metabolites’, ‘short-chain fatty acids’, and ‘choline metabolites’. The correlations of these predictions to biological surface adsorption index descriptors indicated that hydrophobicity-driven interactions contribute most to the overall adsorption affinity, while hydrogen-bond interactions and polarity/polarizability-driven interactions differentiate the affinity to metal and carbon nanomaterials. Next, we use molecular dynamics (MD) simulations to obtain direct molecular information for a selection of vitamins that could not be assessed quantitatively using QSAR models. This showed how large and flexible metabolites can gain stability on the nanomaterial surface via conformational changes. Additionally, unconstrained MD simulations provided excellent support for the main interaction types identified by QSAR analysis. Combined, these results enable assessing the adsorption affinity for many enteric microbial metabolites quantitatively and support the qualitative assessment of an even larger set of complex and biologically relevant microbial metabolites to carbon and metal nanomaterials.

Stress responses of sulfate-reducing bacteria sludge upon exposure to polyethylene microplastics

The stress responses of sulfate-reducing bacteria (SRB) sludge to polyethylene (PE) microplastic exposure were revealed for the first time. In this study, a lab-scale sulfate-reducing up-flow sludge bed reactor was continuously operated with different concentrations of PE microplastics in the feed (20, 100, and 500 microplastic particles (MPs)/L). Exposure to low levels of PE microplastics (i.e., 20 MPs/L) had a limited effect on SRB consortia, whereas higher levels of PE microplastics imposed apparent physiological stresses on SRB consortia. Despite this, the overall reactor performance, i.e., chemical oxygen demand removal and sulfate conversion, was less affected by prolonged exposure to PE microplastics. Moreover, as the concentration of PE microplastics increased, the SRB consortia promoted the production of extracellular polymeric substances to a greater extent, especially the secretion of proteins. As a result, protective effects against the cytotoxicity of PE microplastics were provided. Batch experiments further demonstrated that leaching additives from PE microplastics (including acetyl tri-n‑butyl citrate and bisphenol A, concentrations up to 5 μg/g sludge) exerted only a minor effect on the activity of SRB consortia. Additionally, microbial community analysis revealed active and potentially efficient sulfate reducers at different operational stages. Our results provide insight into the stress responses of SRB sludge under PE microplastic exposure and suggested that SRB consortia can gradually adapt to and resist high levels of PE microplastics. These findings may promote a better understanding of the stable operation of SRB sludge systems under specific environmental stimuli for practical applications.

Antimicrobial Effects of Nanostructured Rare-Earth-Based Orthovanadates

The search for novel antimicrobial agents is of huge importance. Nanomaterials can come to the rescue in this case. The aim of this study was to assess the cytotoxicity and antimicrobial effects of rare-earth-based orthovanadate nanoparticles. The cytotoxicity against host cells and antimicrobial activity of LaVO₄:Eu³⁺ and GdVO₄:Eu³⁺ nanoparticles were analyzed. Effects of nanomaterials on fibroblasts were assessed by MTT, neutral red uptake and scratch assays. The antimicrobial effects were evaluated by the micro-dilution method estimating the minimum inhibitory concentration (MIC) of nanoparticles against various strains of microorganisms, DNA cleavage and biofilm inhibition. GdVO₄:Eu³⁺ nanoparticles were found to be less toxic against eukaryotic cells compared with LaVO₄:Eu³⁺. Both nanoparticles exhibited antimicrobial activity and the highest MIC values were 64 mg/L for E. hirae, E. faecalis and S. aureus shown by GdVO₄:Eu³⁺ nanoparticles. Nanoparticles demonstrated good DNA cleavage activity and induction of double-strand breaks in supercoiled plasmid DNA even at the lowest concentrations used. Both nanoparticles showed the biofilm inhibition activity against S. aureus at 500 mg/L and reduced the microbial cell viability. Taken the results of host toxicity and antimicrobial activity studies, it can be assumed that GdVO₄:Eu³⁺ nanoparticles are more promising antibacterial agents compared with LaVO₄:Eu³⁺ nanoparticles.

Research trends and hotspots of aquatic biofilms in freshwater environment during the last three decades: a critical review and bibliometric analysis

Freshwater periphytic biofilms (FPBs), existing widely in various aquatic environments, have attracted extensive attention for many years. In the present study, a bibliometric analysis based on Web of Science Core Collection (WoSCC) was used to understand the research progress, trends, and hot topics of FPBs qualitatively and quantitatively. The results indicated that publications on FPBs have increased from 1991 to 2020 rapidly, and researchers have focused more on the areas of environmental sciences, microbiology, and marine freshwater biology. The most influential countries were mainly the USA, Spain, France, and Germany. Cooperation network analysis reflected that the USA and its affiliated institutions played crucial roles in the research of FPB cooperation, but the collaboration between core author groups still fell short. Based on the analysis of top 20 high-cited FPB documents over the last 30 years, research hotspots mainly included micro-observation and assembly mechanisms of FPBs; interactions of FPBs and pollutants including heavy metals, antibiotic resistance genes, pathogens, organic pollutants, and nanoparticles; and the role of FPBs for biogeochemical cycling, especially nitrogen cycling. Additionally, future research directions were proposed. Overall, this study provides a comprehensive and systematic overview of FPBs, which is useful for research development and researchers who are interested in this area.

Self-defense mechanisms of microorganisms from the antimicrobial effect of silver nanoparticles: Highlight the role of extracellular polymeric substances

Silver nanoparticles (AgNPs) are nowadays widely utilized in various fields due to their unique antimicrobial properties. Extracellular polymeric substances (EPS) excreted by microorganisms might affect the transformations and antibacterial efficacy of AgNPs. In the present study, the effects of EPS released by Escherichia coli (E. coli) on the dissolution and sulfidation of AgNPs as well as the associated growth inhibition to E. coli were systematically investigated. The formation of EPS-corona caused the reduced exposure of (111) facets of AgNPs due to the preferential binding with aromatic protein components in EPS. The EPS inhibited AgNPs dissolution, while facilitated reductive transformation of the released Ag⁺ to Ag⁰ under simulated sunlight. Additionally, EPS enhanced the colloidal stability and reduced electrostatic repulsive of AgNPs, which favored the access of sulfide and significantly promoted the sulfidation of AgNPs under simulated sunlight, further reducing the available dissolved Ag⁺ ions. Consequently, the EPS relieved the antibacterial activity of AgNPs to E. coli. These findings highlight the importance of microbial EPS in the transformations and bactericidal effect of AgNPs, which provide clues for the development of AgNPs-based antibacterial strategies.

Helicobacter pylori biofilms are disrupted by nanostructured lipid carriers: A path to eradication?

Bacterial biofilms account for 80% of all chronic infections, with cells being up to 1000 times more resistant to antibiotics than their planktonic counterparts. The recently discovered ability of Helicobacter pylori to form biofilms once again highlights why this bacterium is one of the most successful human pathogens. The current treatments failure rate reaches 40% of cases, emphasizing that new therapeutic options are a pressing need. Nanostructured lipid carriers (NLC), with and without docosahexaenoic acid (DHA), were very effective against H. pylori planktonic cells but their effect on H. pylori biofilms was unknown. Here, DHA-loaded NLC (DHA-NLC) and NLC without any drug (blank NLC) were tested on an optimized H. pylori in vitro floating mature biofilm model. DHA-NLC and blank NLC reduced the total biofilm biomass and had a bactericidal effect against both biofilm and planktonic bacteria in all the concentrations tested (0.125-2 mg/mL). DHA-NLC achieved biofilm biomass reduction in a concentration ~ 8 times lower than blank NLC (0.125 vs 1 mg/mL, respectively). Both NLC were bactericidal at the lowest concentration tested (0.125 mg/mL) although with different efficiency, i.e. a decrease of ∼6 log₁₀ for DHA-NLC and ∼5 log₁₀ for blank NLC. In addition, the equivalent amount of free DHA (3.1 μM) only reduced bacterial viability in ∼2 log₁₀, demonstrating the synergistic effect of DHA and NLC in the treatment of H. pylori biofilms. Nevertheless, although viable bacteria were not detected by colony forming unit (CFU) counting after treatment with both NLC, confocal microscopy imaging highlighted that some H. pylori cells remained alive. In addition, scanning electron microscopy (SEM) analysis confirmed an increase in bacteria with a coccoid morphology after treatment, suggesting a transition to a viable but non-culturable (VBNC) state. Altogether, it is herein established that NLC, even without any drug, are promising for the management of H. pylori bacteria organized in biofilms, opening new perspectives for the eradication of this gastric pathogen.

Monitoring and imaging pH in biofilms utilizing a fluorescent polymeric nanosensor

Biofilms are ubiquitous in nature and in the man-made environment. Given their harmful effects on human health, an in-depth understanding of biofilms and the monitoring of their formation and growth are important. Particularly relevant for many metabolic processes and survival strategies of biofilms is their extracellular pH. However, most conventional techniques are not suited for minimally invasive pH measurements of living biofilms. Here, a fluorescent nanosensor is presented for ratiometric measurements of pH in biofilms in the range of pH 4.5–9.5 using confocal laser scanning microscopy. The nanosensor consists of biocompatible polystyrene nanoparticles loaded with pH-inert dye Nile Red and is surface functionalized with a pH-responsive fluorescein dye. Its performance was validated by fluorometrically monitoring the time-dependent changes in pH in E. coli biofilms after glucose inoculation at 37 °C and 4 °C. This revealed a temperature-dependent decrease in pH over a 4-h period caused by the acidifying glucose metabolism of E. coli. These studies demonstrate the applicability of this nanosensor to characterize the chemical microenvironment in biofilms with fluorescence methods.

Peptides to Overcome the Limitations of Current Anticancer and Antimicrobial Nanotherapies

Biomedical research devotes a huge effort to the development of efficient non-viral nanovectors (NV) to improve the effectiveness of standard therapies. NVs should be stable, sustainable and biocompatible and enable controlled and targeted delivery of drugs. With the aim to foster the advancements of such devices, this review reports some recent results applicable to treat two types of pathologies, cancer and microbial infections, aiming to provide guidance in the overall design of personalized nanomedicines and highlight the key role played by peptides in this field. Additionally, future challenges and potential perspectives are illustrated, in the hope of accelerating the translational advances of nanomedicine.

Nanocarriers for combating biofilms: advantages and challenges

Bacterial biofilms are highly resistant to antibiotics and pose a great threat to human and animal health. The control and removal of bacterial biofilms have become an important topic in the field of bacterial infectious diseases. Nanocarriers show great anti-biofilm potential because of their small particle size and strong permeability. In this review, the advantages of nanocarriers for combating biofilms are analyzed. Nanocarriers can act on all stages of bacterial biofilm formation and diffusion. They can improve the scavenging effect of biofilm by targeting biofilm, destroying extracellular polymeric substances, and enhancing the biofilm permeability of antimicrobial substances. Nanocarriers can also improve the antibacterial ability of antimicrobial drugs against bacteria in biofilm by protecting the loaded drugs and controlling the release of antimicrobial substances. Additionally, we emphasize the challenges faced in using nanocarrier formulations and translating them from a preclinical level to the clinical setting.

Polymicrobial biofilms related to dental implant diseases: unravelling the critical role of extracellular biofilm matrix

Biofilms are complex tri-dimensional structures that encase microbial cells in an extracellular matrix comprising self-produced polymeric substances. The matrix rich in extracellular polymeric substance (EPS) contributes to the unique features of biofilm lifestyle and structure, enhancing microbial accretion, biofilm virulence, and antimicrobial resistance. The role of the EPS matrix of biofilms growing on biotic surfaces, especially dental surfaces, is largely unravelled. To date, there is a lack of a broad overview of existing literature concerning the relationship between the EPS matrix and the dental implant environment and its role in implant-related infections. Here, we discuss recent advances in the critical role of the EPS matrix on biofilm growth and virulence on the dental implant surface and its effect on the etiopathogenesis and progression of implant-related infections. Similar to other biofilms associated with human diseases/conditions, EPS-enriched biofilms on implant surfaces promote microbial accumulation, microbiological shift, cross-kingdom interaction, antimicrobial resistance, biofilm virulence, and, consequently, peri-implant tissue damage. But intriguingly, the protagonism of EPS role on implant-related infections and the development of matrix-target therapeutic strategies has been neglected. Finally, we highlight the need for more in-depth analyses of polymicrobial interactions within EPS matrix and EPS-targeting technologies' rationale for disrupting the complex biofilm microenvironment with more outstanding translation to implant applications in the near future.

Antibacterial and Biofilm-Eradicating Activities of pH-Responsive Vesicles against Pseudomonas aeruginosa

The formation of biofilms by a microcolony of bacteria is a significant burden on the healthcare industry due to difficulty eradicating it. In this study, pH-responsive vesicles capable of releasing apramycin (APR), a model aminoglycoside antibiotic, in response to the low pH typical of establishedPseudomonas aeruginosa biofilms resulted in improved eradication of existing biofilms in comparison to the free drug. The amphiphilic polymeric vesicle (PV) comprised of block polymer poly (ethylene glycol)-block-poly 2-(dimethylamino) ethyl methacrylate (mPEG-b-pDEAEMA) averaged 128 nm. The drug encapsulation content of APR in PV/APR was confirmed to be 28.2%, and the drug encapsulation efficiency was confirmed to be 51.2%. At pH 5.5, PV/APR released >90% APR after 24 h compared to <20% at pH 7.4. At pH 5.5, protonation of the pDEAEMA block results in a zeta potential of +23 mV compared to a neutral zeta potential of +2.2 mV at pH 7.4. Confocal microscopy, flow cytometry, and scanning electron microscopy reveal that the positively charged vesicles can compromise the integrity of the planktonic bacterial membrane in a pH-dependent manner. In addition, PV/APR is able to diffuse into mature biofilms to release APR in the acidic milieu of biofilm bacteria, and PV/APR was more efficient at eliminating preexisting biofilms compared to free APR at 128 and 256 μg/mL. This study reveals that dynamic charge density in response to pH can lead to differential levels of interactions with the biofilm and bacterial membrane. This effectively results in enhanced antibacterial and antibiofilm properties against both planktonic and difficult-to-treat biofilm bacteria at concentrations significantly lower than those of the free drug. Overall, this pH-responsive vesicle could be especially promising for treating biofilm-associated infectious diseases.

Microbially-derived cocktail of carbohydrases as an anti-biofouling agents: a 'green approach'

Enzymes, also known as biocatalysts, display vital properties like high substrate specificity, an eco-friendly nature, low energy inputs, and cost-effectiveness. Among their numerous known applications, enzymes that can target biofilms or their components are increasingly being investigated for their anti-biofouling action, particularly in healthcare, food manufacturing units and environmental applications. Enzymes can target biofilms at different levels like during the attachment of microorganisms, formation of exopolymeric substances (EPS), and their disruption thereafter. In this regard, a consortium of carbohydrases that can target heterogeneous polysaccharides present in the EPS matrix may provide an effective alternative to conventional chemical anti-biofouling methods. Further, for complete annihilation of biofilms, enzymes can be used alone or in conjunction with other antimicrobial agents. Enzymes hold the promise to replace the conventional methods with greener, more economical, and more efficient alternatives. The present article explores the potential and future perspectives of using carbohydrases as effective anti-biofilm agents.

Improved methane production with redox-active/conductive biochar amendment by establishing spatial ecological niche and mediating electron transfer

The multifunctional roles of biochar as an additive in improving the performance of anaerobic digestion (AD) has not been perfectly understood. In this study, the effects of different biochars on AD and the enhanced mechanisms were explored. The CH₄ productions were significantly improved with an increase of 45.9%, 28.3% and 16.5% by amendment with biochar pyrolyzed at 300℃ (BC300), 450℃ (BC450) and 600℃ (BC600), respectively. The tightly-bound communities were established on biochar at the initial stage of fermentation and functional microbes were selectively enriched/colonized in biochar-amended systems. Distinctive loosely-bound microbial communities were observed in BC300 and BC600 amended systems, among which electroactive Desulforhabdus and Clostridiales were the dominant bacteria. Biochar amendments also led to the formation of distinctive spatial ecological niches and the selection preference of microbes for specific spatial locations. These results provided new insights in revealing the potential mechanisms of enhanced AD performance by biochar amendment.

The Role of Extracellular Polymeric Substances in the Toxicity Response of Anaerobic Granule Sludge to Different Metal Oxide Nanoparticles

Wastewater treatment plants (WWTP) are regarded as the last barriers for the release of incompletely separated and recycled nanoparticles (NPs) into the environment. Despite the importance and ubiquity of microbial extracellular polymeric substances (EPSs) in the complex wastewater matrix, the interaction between NPs and EPSs of anaerobic microflora involved in wastewater treatment and the resultant impact on the biomass metabolomics are unclear. Thus, the impacts of different metal oxide (TiO₂, ZnO, and CuO) NPs on functional bacteria in anaerobic granular sludge (AGS) and the possible toxicity mechanisms were investigated. In particular, the binding quality, enhanced resistance mechanism, and chemical fractional contribution of EPSs from AGS against the nanotoxicity of different NPs was assessed. The results showed that CuO NPs caused the most severe inhibition towards acetoclastic and hydrogenotrophic methanogens, followed by ZnO NPs, whereas TiO₂ NPs caused no inhibition to methanogenesis. Excessive EPS production, especially the protein-like substances, was an effective strategy for reducing certain NPs’ toxicity by immobilizing NPs away from AGS cells, whereas the metabolism restriction on inner microorganisms of AGS induced by CuO NPs can deteriorate the protective role of EPS, indicating that the roles of EPS may not be amenable to generalizations. Further investigations with lactate dehydrogenase (LDH) and reactive oxygen species (ROS) assays indicated that there are greatly essential differences between the toxicity mechanisms of metal NPs to AGS, which varied depending on the NPs’ type and dosage. In addition, dynamic changes in the responses of EPS content to different NPs can result in a significant shift in methanogenic and acidogenic microbial communities. Thus, the production and composition of EPSs will be a key factor in determining the fate and potential effect of NPs in the complex biological matrix. In conclusion, this study broadens the understanding of the inhibition mechanisms of metal oxide NPs on the AGS process, and the influence of EPSs on the fate, behavior, and toxicity of NPs.

Titanium Dental Implants: An Overview of Applied Nanobiotechnology to Improve Biocompatibility and Prevent Infections

This review addresses the different aspects of the use of titanium and its alloys in the production of dental implants, the most common causes of implant failures and the development of improved surfaces capable of stimulating osseointegration and guaranteeing the long-term success of dental implants. Titanium is the main material for the development of dental implants; despite this, different surface modifications are studied aiming to improve the osseointegration process. Nanoscale modifications and the bioactivation of surfaces with biological molecules can promote faster healing when compared to smooth surfaces. Recent studies have also pointed out that gradual changes in the implant, based on the microenvironment of insertion, are factors that may improve the integration of the implant with soft and bone tissues, preventing infections and osseointegration failures. In this context, the understanding that nanobiotechnological surface modifications in titanium dental implants improve the osseointegration process arouses interest in the development of new strategies, which is a highly relevant factor in the production of improved dental materials.

Polyethyleneimine Functionalized Mesoporous Magnetic Nanoparticles with Enhanced Antibacterial and Antibiofilm Activity in an Alternating Magnetic Field

Despite a lot of research on the antibacterial effect of Fe₃O₄ nanoparticles, their interactions with biofilm matrix have not been well understood. The surface charge of nanoparticles mainly determines their ability to adhere on the biofilm. In this work, negatively charged Fe₃O₄ nanoparticles were synthesized via a trisodium citrate-assisted solvothermal method and then the surfaces were functionalized using polyethyleneimine (PEI) to obtain positively charged Fe₃O₄ nanoparticles. The antibacterial and antibiofilm activities of both negatively and positively charged Fe₃O₄ nanoparticles in an alternating magnetic field were then systematically investigated. The positively charged Fe₃O₄ nanoparticles showed a strong self-adsorbed attachment ability to the planktonic and sessile cells, resulting in a better antibacterial activity and enhanced biofilm eradication performance compared to the conventional Fe₃O₄ nanoparticles with negative charges. Fe₃O₄@PEI nanoparticles produced physical stress and thermal damage in response to an alternating magnetic field, inducing the accumulation of intracellular reactive oxygen species into live bacterial cells, bacterial membrane damage, and biofilm dispersion. Utilizing an alternating magnetic field along with positively charged nanoparticles leads to a synergistic antibacterial approach to improve the antibiofilm performance of magnetic nanoparticles.

A pH-Gated Functionalized Hollow Mesoporous Silica Delivery System for Photodynamic Sterilization in Staphylococcus aureus Biofilm

Multidrug-resistant bacteria are increasing, particularly those embedded in microbial biofilm. These bacteria account for most microbial infections in humans. Traditional antibiotic treatment has low efficiency in sterilization of biofilm-associated pathogens, and thus the development of new approaches is highly desired. In this study, amino-modified hollow mesoporous silica nanoparticles (AHMSN) were synthesized and used as the carrier to load natural photosensitizer curcumin (Cur). Then glutaraldehyde (GA) and polyethyleneimine (PEI) were used to seal the porous structure of AHMSN by the Schiff base reaction, forming positively charged AHMSN@GA@PEI@Cur. The Cur delivery system can smoothly diffuse into the negatively charged biofilm of Staphylococcus aureus (S. aureus). Then Cur can be released to the biofilm after the pH-gated cleavage of the Schiff base bond in the slightly acidic environment of the biofilm. After the release of the photosensitizer, the biofilm was irradiated by the blue LED light at a wavelength of 450 nm and a power of 37.4 mV/cm² for 5 min. Compared with the control group, the number of viable bacteria in the biofilm was reduced by 98.20%. Therefore, the constructed pH-gated photosensitizer delivery system can efficiently target biofilm-associated pathogens and be used for photodynamic sterilization, without the production of antibiotic resistance.

Synthesis of Natural Nano-Hydroxyapatite from Snail Shells and Its Biological Activity: Antimicrobial, Antibiofilm, and Biocompatibility

Hydroxyapatite nanoparticles (HAn) have been produced as biomaterial from biowaste, especially snail shells (Atactodea glabrata). It is critical to recycle the waste product in a biomedical application to overcome antibiotic resistance as well as biocompatibility with normal tissues. Moreover, EDX, TEM, and FT-IR analyses have been used to characterize snail shells and HAn. The particle size of HAn is about 15.22 nm. Furthermore, higher inhibitory activity was observed from HAn than the reference compounds against all tested organisms. The synthesized HAn has shown the lowest MIC values of about 7.8, 0.97, 3.9, 0.97, and 25 µg/mL for S. aureus, B. subtilis, K. pneumonia, C. albicans, and E. coli, respectively. In addition, the HAn displayed potent antibiofilm against S. aureus and B. subtilis. According to the MTT, snail shell and HAn had a minor influence on the viability of HFS-4 cells. Consequently, it could be concluded that some components of waste, such as snail shells, have economic value and can be recycled as a source of CaO to produce HAn, which is a promising candidate material for biomedical applications.

Hurdle technology using encapsulated enzymes and essential oils to fight bacterial biofilms

Biofilm formation on abiotic surfaces has become a major public health concern because of the serious problems they can cause in various fields. Biofilm cells are extremely resistant to stressful conditions, because of their complex structure impedes antimicrobial penetration to deep-seated cells. The increased resistance of biofilm to currently applied control strategies underscores the urgent need for new alternative and/or supplemental eradication approaches. The combination of two or more methods, known as Hurdle technology, offers an excellent option for the highly effective control of biofilms. In this perspective, the use of functional enzymes combined with biosourced antimicrobial such as essential oil (EO) is a promising alternative anti-biofilm approach. However, these natural antibiofilm agents can be damaged by severe environmental conditions and lose their activity. The microencapsulation of enzymes and EOs is a promising new technology for enhancing their stability and improving their biological activity. This review article highlights the problems related to biofilm in various fields, and the use of encapsulated enzymes with essential oils as antibiofilm agents. KEY POINTS: • Problems associated with biofilms in the food and medical sectors and their subsequent risks on health and food quality. • Hurdle technology using enzymes and essential oils is a promising strategy for an efficient biofilms control. • The microencapsulation of enzymes and essential oils ensures their stability and improves their biological activities.

Advances in the Sensing and Treatment of Wound Biofilms

Wound biofilms represent a particularly challenging problem in modern medicine. They are increasingly antibiotic resistant and can prevent the healing of chronic wounds. However, current treatment and diagnostic options are hampered by the complexity of the biofilm environment. In this review, we present new chemical avenues in biofilm sensors and new materials to treat wound biofilms, offering promise for better detection, chemical specificity, and biocompatibility. We briefly discuss existing methods for biofilm detection and focus on novel, sensor-based approaches that show promise for early, accurate detection of biofilm formation on wound sites and that can be translated to point-of-care settings. We then discuss technologies inspired by new materials for efficient biofilm eradication. We focus on ultrasound-induced microbubbles and nanomaterials that can both penetrate the biofilm and simultaneously carry active antimicrobials and discuss the benefits of those approaches in comparison to conventional methods.

Emerging nanotechnologies for targeting antimicrobial resistance

Antimicrobial resistance is a leading cause of mortality worldwide. Without newly approved antibiotics and antifungals being brought to the market, resistance is being developed to the ones currently available to clinicians. The reason is the applied evolutionary pressure to bacterial and fungal species due to the wide overuse of common antibiotics and antifungals in clinical practice and agriculture. Biofilms harbour antimicrobial-resistant subpopulations, which make their antimicrobial treatment even more challenging. Nanoparticle-based technologies have recently been shown to successfully overcome antimicrobial resistance in both planktonic and biofilms phenotypes. This results from the combination of novel nanomaterial research and classic antimicrobial therapies which promise to deliver a whole new generation of high-performance active nanocarrier systems. This review discusses the latest developments of promising nanotechnologies with applications against resistant pathogens and evaluates their potential and feasibility for use in novel antimicrobial therapies.

Plausible Mechanistic Insights in Biofilm Eradication Potential against Candida spp. Using In Situ-Synthesized Tyrosol-Functionalized Chitosan Gold Nanoparticles as a Versatile Antifouling Coating on Implant Surfaces

In the present study, tyrosol-functionalized chitosan gold nanoparticles (Chi-TY-AuNPs) were prepared as an alternative treatment strategy to combat fungal infections. Various biophysical techniques were used to characterize the synthesized Chi-TY-AuNPs. The antifungal and antibiofilm activities of Chi-TY-AuNPs were evaluated against Candida albicans and C. glabrata, and efforts have been made to elucidate the possible mechanism of action. Chi-TY-AuNPs showed a high fungicidal effect against both sessile and planktonic cells of Candida spp. Additionally, Chi-TY-AuNPs completely eradicated (100%) the mature biofilms of both the Candida spp. FESEM analysis highlighted the morphological alterations in Chi-TY-AuNP-treated Candida biofilm cells. The effect of Chi-TY-AuNPs on the ECM components showed significant reduction in protein content in the C. glabrata biofilm and substantial decrease in extracellular DNA content of both the Candida spp. ROS generation analysis using DCFDA-PI staining showed high ROS levels in both the Candida spp., whereas pronounced ROS production was observed in the Chi-TY-AuNP-treated C. glabrata biofilm. Biochemical analysis revealed decreased ergosterol content in Chi-TY-AuNP-treated C. glabrata cells, while inconsequential changes were observed in C. albican s. Furthermore, the transcriptional expression of selected genes (ergosterol biosynthesis, efflux, sterol importer, and glucan biogenesis) was reduced in C. glabrata in response to Chi-TY-AuNPs except ERG11 and CDR1. Conclusively, the result showed the biofilm inhibition and biofilm eradication efficacy of Chi-TY-AuNPs in both the Candida spp. Findings of the present study manifest Chi-TY-AuNPs as a potential therapeutic solution to Candida biofilm-related chronic infections and overcome biofilm antifungal resistance.

Size-dependent photothermal antibacterial activity of Ti3C2Tx MXene nanosheets against methicillin-resistant Staphylococcus aureus

Developing antibiotics-independent antibacterial materials is of great importance for combating drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). MXene (transition metal carbides and nitrides), a class of novel 2D nanomaterials, has shown great potentials in biomedical areas. However, the effect of MXene size on its properties and bioactivity is still unknown. Herein, we report for the first time that the antibacterial photothermal therapy efficacy of Ti₃C₂T_x MXene nanosheets is size-dependent. Three MXene suspensions with small size of 196 nm (MX-s), medium size of 347 nm (MX-m) and large size of 497 nm (MX-l) were prepared via ultrasonication. Upon NIR irradiation for 5 min, the temperature of MXene suspensions (10 μg/mL) increased to 64, 60 and 56 °C for MX-s, MX-m and MX-l, respectively. Accordingly, the viability loss of MRSA induced by MX-s, MX-m and MX-l under NIR was 93%, 69% and 56%, respectively. The in vivo study in the MRSA-infected mouse model showed that the photothermal therapy efficacy of MX-s was comparable to that of the positive control vancomycin. This is the first report on the size-dependent photothermal effect and photothermal antibacterial activity of MXene, which may guide the development of MXene-based therapeutics in the future. In addition, the drug-free antibacterial therapy has great implications for the treatment of antibiotics-resistant bacteria infections.

D-arginine Enhances the Effect of Alpha-Amylase on Disassembling Actinomyces viscosus Biofilm

Peri-implantitis is the leading cause of dental implant failure, initially raised by biofilm accumulation on the implant surface. During the development of biofilm, Actinomyces viscosus (A. viscosus) plays a pivotal role in initial attachment as well as the bacterial coaggregation of multispecies pathogens. Hence, eliminating the A. viscosus-associated biofilm is fundamental for the regeneration of the lost bone around implants. Whereas clinical evidence indicated that antimicrobials and debridement did not show significant effects on the decontamination of biofilm on the implant surface. In this study, alpha-amylase was investigated for its effects on disassembling A. viscosus biofilm. Then, in order to substantially disperse biofilm under biosafety concentration, D-arginine was employed to appraise its enhancing effects on alpha-amylase. In addition, molecular dynamics simulations and molecular docking were conducted to elucidate the mechanism of D-arginine enhancing alpha-amylase. 0.1–0.5% alpha-amylase showed significant effects on disassembling A. viscosus biofilm, with definite cytotoxicity toward MC3T3-E1 cells meanwhile. Intriguingly, 8 mM D-arginine drastically enhanced the eradication of A. viscosus biofilm biomass by 0.01% alpha-amylase with biosafety in 30 min. The exopolysaccharides of biofilm were also thoroughly hydrolyzed by 0.01% alpha-amylase with 8 mM D-arginine. The biofilm thickness and integrity were disrupted, and the exopolysaccharides among the extracellular matrix were elusive. Molecular dynamics simulations showed that with the hydrogen bonding of D-arginine to the catalytic triad and calcium-binding regions of alpha-amylase, the atom fluctuation of the structure was attenuated. The distances between catalytic triad were shortened, and the calcium-binding regions became more stable. Molecular docking scores revealed that D-arginine facilitated the maltotetraose binding process of alpha-amylase. In conclusion, these results demonstrate that D-arginine enhances the disassembly effects of alpha-amylase on A. viscosus biofilm through potentiating the catalytic triad and stabilizing the calcium-binding regions, thus providing a novel strategy for the decontamination of biofilm contaminated implant surface.

Genetic Relatedness, Antibiotic Resistance, and Effect of Silver Nanoparticle on Biofilm Formation by Clostridium perfringens Isolated from Chickens, Pigeons, Camels, and Human Consumers

In this study, we determined the prevalence and toxin types of antibiotic-resistant Clostridium perfringens in chicken, pigeons, camels, and humans. We investigated the inhibitory effects of AgNPs on biofilm formation ability of the isolates and the genetic relatedness of the isolates from various sources determined using RAPD-PCR. Fifty isolates were identified using PCR, and all the isolates were of type A. The cpe and cpb2 genes were detected in 12% and 56% of the isolates, respectively. The effect of AgNPs on biofilm production of six representative isolates indicated that at the highest concentration of AgNPs (100 µg/mL), the inhibition percentages were 80.8–82.8%. The RAPD-PCR patterns of the 50 C. perfringens isolates from various sources revealed 33 profiles and four clusters, and the discriminatory power of RAPD-PCR was high. Multidrug-resistant C. perfringens isolates are predominant in the study area. The inhibition of biofilm formation by C. perfringens isolates was dose-dependent, and RAPD-PCR is a promising method for studying the genetic relatedness between the isolates from various sources. This is the first report of AgNPs’ anti-biofilm activity against C. perfringens from chickens, pigeons, camels, and humans, to the best of our knowledge.

Recent Strategies to Combat Biofilms Using Antimicrobial Agents and Therapeutic Approaches

Biofilms are intricate bacterial assemblages that attach to diverse surfaces using an extracellular polymeric substance that protects them from the host immune system and conventional antibiotics. Biofilms cause chronic infections that result in millions of deaths around the world every year. Since the antibiotic tolerance mechanism in biofilm is different than that of the planktonic cells due to its multicellular structure, the currently available antibiotics are inadequate to treat biofilm-associated infections which have led to an immense need to find newer treatment options. Over the years, various novel antibiofilm compounds able to fight biofilms have been discovered. In this review, we have focused on the recent and intensively researched therapeutic techniques and antibiofilm agents used for biofilm treatment and grouped them according to their type and mode of action. We also discuss some therapeutic approaches that have the potential for future advancement.

Prochloraz alone or in combination with nano-CuO promotes the conjugative transfer of antibiotic resistance genes between Escherichia coli in pure water

Conjugative plasmid transfer is a major contributor to the spread of antibiotic resistance genes (ARGs). However, the role of conventional fungicides on conjugative plasmid transfer has been neglected. Based on the condition that the increasing use of the combination of nano- and conventional fungicides will lead to combined contamination, the effects of a conventional fungicide prochloraz alone or in combination with nano-CuO on the conjugation of plasmid RP4 between Escherichia coli in phosphate-buffered saline were investigated in this study. The results demonstrated that 50 µg/L prochloraz alone significantly increased the conjugative transfer by 1.82 folds. The combination of 100 µg/L nano-CuO and prochloraz at 5, 50, and 500 µg/L significantly increased the conjugation by 2.56, 3.61, and 2.13 folds, respectively. The promotion of conjugative transfer of ARGs mediated by fungicides is mainly attributed to (i) the increased cell membrane permeability, (ii) the increased cell adhesion via enhancing the synthesis of polysaccharides in extracellular polymeric substances, and (iii) the up-regulation of the genes relevant to conjugation, oxidative stress, SOS response, outer membrane, polysaccharide export, intercellular adhesion, and ATP synthesis. Our findings provide evidence for the contribution of fungicides to ARGs transfer, which is significant to control the risk of ARGs dissemination.

Influence of extracellular polymeric substances on the heteroaggregation between CeO2 nanoparticles and soil mineral particles

Interaction with soil mineral particles (SMPs) and organic matters can significantly determine the fate of nanoparticles (NPs) in the environment such as waters, sediments, and soils. In this study, the heteroaggregation of CeO₂ NPs with different soil minerals (kaolinite, montmorillonite, goethite and hematite) and the influence of extracellular polymeric substance (EPS) were studied. The obvious heteroaggregation between CeO₂ NPs with different SMPs were demonstrated via co-settling and aggregation kinetics experiments. The variety in the heteroaggregation between CeO₂ NPs with different SMPs is mainly induced by the difference in their surface properties, such as surface charge, specific surface areas and surface complexation. The presence of EPS can result in great inhibition on the heteroaggregation between CeO₂ NPs with the positive charged goethite by enhancing the electrostatic repulsion between NPs and mineral colloids. However, the influence of EPS on the interaction between CeO₂ NPs with negative charged SMPs is more dependent on the steric stabilization. The presence of EPS may promote the migration of CeO₂ NPs in environment and then increase their risks to human health and ecosystems. These findings contribute to better understanding interactions between NPs and SMPs and have important implications on predicting the behaviors and risks of NPs in the natural environment.

Nanoparticles approach to eradicate bacterial biofilm-related infections: A critical review

Biofilm represents one of the crucial factors for the emergence of multi-drug resistance bacterial infections. The high mortality, morbidity and medical device-related infections are associated with biofilm formation, which requires primarily seek alternative treatment strategies. Recently, nanotechnology has emerged as a promising method for eradicating bacterial biofilm-related infection. The efficacy of nanoparticles (NPs) against bacterial infections interest great attention, and the researches on the subject are rapidly increasing. However, the majority of studies continue to focus on the antimicrobial effects of NPs in vitro, while only a few achieved in vivo and very few registered as clinical trials. The present review aimed to organize the scattered available information regarding NPs approach to eradicate bacterial biofilm-related infections. The current review highlighted the advantages and disadvantages associated with this approach, in addition to the challenges that prevent reaching the clinical applications. It was appeared that the production of NPs either as antimicrobials or as drug carriers requires further investigations to overcome the obstacles associated with their kinetic and biocompatibility.

Improving Antibacterial Activity of a HtrA Protease Inhibitor JO146 against Helicobacter pylori: A Novel Approach Using Microfluidics-Engineered PLGA Nanoparticles

Nanoparticle drug delivery systems have emerged as a promising strategy for overcoming limitations of antimicrobial drugs such as stability, bioavailability, and insufficient exposure to the hard-to-reach bacterial drug targets. Although size is a vital colloidal feature of nanoparticles that governs biological interactions, the absence of well-defined size control technology has hampered the investigation of optimal nanoparticle size for targeting bacterial cells. Previously, we identified a lead antichlamydial compound JO146 against the high temperature requirement A (HtrA) protease, a promising antibacterial target involved in protein quality control and virulence. Here, we reveal that JO146 was active against Helicobacter pylori with a minimum bactericidal concentration of 18.8–75.2 µg/mL. Microfluidic technology using a design of experiments approach was utilized to formulate JO146-loaded poly(lactic-co-glycolic) acid nanoparticles and explore the effect of the nanoparticle size on drug delivery. JO146-loaded nanoparticles of three different sizes (90, 150, and 220 nm) were formulated with uniform particle size distribution and drug encapsulation efficiency of up to 25%. In in vitro microdilution inhibition assays, 90 nm nanoparticles improved the minimum bactericidal concentration of JO146 two-fold against H. pylori compared to the free drug alone, highlighting that controlled engineering of nanoparticle size is important in drug delivery optimization.

Metal Complexes—A Promising Approach to Target Biofilm Associated Infections

Microbial biofilms are represented by sessile microbial communities with modified gene expression and phenotype, adhered to a surface and embedded in a matrix of self-produced extracellular polymeric substances (EPS). Microbial biofilms can develop on both prosthetic devices and tissues, generating chronic and persistent infections that cannot be eradicated with classical organic-based antimicrobials, because of their increased tolerance to antimicrobials and the host immune system. Several complexes based mostly on 3D ions have shown promising potential for fighting biofilm-associated infections, due to their large spectrum antimicrobial and anti-biofilm activity. The literature usually reports species containing Mn(II), Ni(II), Co(II), Cu(II) or Zn(II) and a large variety of multidentate ligands with chelating properties such as antibiotics, Schiff bases, biguanides, N-based macrocyclic and fused rings derivatives. This review presents the progress in the development of such species and their anti-biofilm activity, as well as the contribution of biomaterials science to incorporate these complexes in composite platforms for reducing the negative impact of medical biofilms.

Reduction and removal of Cr(VI) in water using biosynthesized palladium nanoparticles loaded Shewanella oneidensis MR-1

In materials science, "green" synthesis has gotten a lot of interest as a reliable, long-lasting, and ecofriendly way to make a variety of materials/nanomaterials, including metal/metal oxide nanomaterials. To accommodate various biological materials, green synthesis of metallic nanoparticles has been used (e.g., bacteria, fungi, algae, and plant extracts). In this work, Shewanella oneidensis MR-1 was used to biosynthesize palladium nanoparticles (bioPd) under aerobic conditions for the Cr(VI) bio-reduction. The size and distribution of bio-Pd are controlled by adjusting the ratio of microbial biomass and palladium precursors. The high cell: Pd ratio has the smallest average particle size of 6.33 ± 1.69 nm. And it has the lowest electrocatalytic potential (-0.132 V) for the oxidation of formic acid, which is 0.158 V lower than commercial Pd/C (5%). Our results revealed that the small size and uniformly distributed extracellular bio-Pd could achieve completely catalytic reduction of 200 mg/L Cr(VI) solution within 10 min, while the commercial Pd/C (5%) need at least 45 min. The bio-Pd materials maintain a high reduction during five cycles. Microorganisms play an important role in the whole process, which can fully disperse palladium nanoparticles, completely reduce Cr(VI), and effectively adsorb Cr(III). This work expands our understanding and provides a reference for the design and development of efficient and green bio-Pd catalysts for environmental pollution control under simple and mild conditions.

Contribution, Composition, and Structure of EPS by In Vivo Exposure to Elucidate the Mechanisms of Nanoparticle-Enhanced Bioremediation to Metals

Bacterial extracellular polymeric substances (EPS) have been recently found to contribute most for metal removal in nanoenhanced bioremediation. However, the mechanism by which NPs affect EPS-metal interactions is not fully known. Here, Halomonas sp. was employed to explore the role of EPS after in vivo exposure to Cd/Pb and polyvinylpyrrolidone (PVP) coated iron oxide nanoparticles (IONPs, 20 mg L^-1) for 72 h. Cd-IONPs produced the highest concentrations of EPS proteins (136.3 mg L^-1), while Cd induced the most production of polysaccharides (241.0 mg L^-1). IONPs increased protein/polysaccharides ratio from 0.2 (Cd) to 1.2 (Cd-IONPs). The increased protein favors the formation of protein coronas on IONPs surface, which would promote Cd adsorption during NP-metal-EPS interaction. FTIR analysis indicated that the coexistence of Cd and IONPs interacted with proteins more strongly than with polysaccharides. Glycosyl monomer analyses suggested mannose and glucose as target sugars for EPS complexation with metals, and IONPs reduced metal-induced changes in monosaccharide profiles. Protein secondary structures changed in all treatments, but we could not distinguish stresses induced by metals from those by IONPs. These findings provide greater understanding of the role of EPS in NP-metal-EPS interaction, providing a better underpinning knowledge for the application of NP-enhanced bioremediation.

Effect of Nano-Silver on Formation of Marine Snow and the Underlying Microbial Mechanism

Roller experiments were conducted to explore the effect of nano-silver on the formation of marine snow and the underlying microbial mechanism. With the increasing concentration of nano-Ag from 1 ng/L to 1 mg/L, the formation and aggregation of marine snow particles were solidly suppressed in a dose-dependent pattern. Moreover, the formed marine snows tended to be thinner fibrous particles with smaller size and increased edge smoothness and compactness in the presence of nano-Ag. The microbial analyses indicated that nano-Ag not only inhibited the development of biomass but also changed the species composition and functional profile of the microbial community. Nano-Ag obviously inhibited most of the abundant species, except for some myxobacteria, which is unfavorable for the microbial community stability. For the microbial functions, some major biological processes including the growth, metabolic, and cellular processes were also inhibited by the high dosage of nano-Ag. The strong microbial inhibition of nano-Ag would contribute to the suppression on the formation of marine snow. Specifically, the function genes of extracellular polymeric substance synthesis and secretion were significantly reduced by nano-Ag, which might be the key and straight microbial factor in suppressing the formation of marine snow.

Biofilm-overproducing Bacillus amyloliquefaciens P29ΔsinR decreases Pb availability and uptake in lettuce in Pb-polluted soil

In this study, one mutant strain P29ΔsinR with increased biofilm production was constructed from a biofilm-producing Bacillus amyloliquefaciens strain P29. Then, the effect of strain P29 and its biofilm-overproducing mutant strain P29ΔsinR on Pb availability and accumulation in lettuce and the associated mechanisms were characterized in the Pb-contaminated soil. The live strains P29 and P29ΔsinR increased the dry masses of roots and edible tissues by 31-74% compared to the controls. The live strains P29 and P29ΔsinR reduced the Pb uptake in the roots by 36-52% and edible tissues by 24-43%, Pb bioconcentration factor by 36-52%, and rhizosphere soil available Pb content by 12-25%, respectively, compared to the controls. The live strains P29 and P29ΔsinR increased the pH, proportion of biofilm-producing bacteria by 46-154%, contents of polysaccharides by 99-139% and proteins by 32-57%, and gene relative abundances of epsC by 7.1-10.2-fold, tasA by 10.3-10.8-fold, and sipW by 6.5-26.1-fold, which were associated with biofilm formation and Pb adsorption in the rhizosphere soils, respectively, compared to the controls. Furthermore, the mutant strain P29ΔsinR showed higher ability to reduce Pb availability and uptake in lettuce and increase the pH, proportion of biofilm-producing bacteria, polysaccharide and protein contents, and relative abundances of these genes. These results showed that the biofilm-overproducing strain P29ΔsinR induced lower Pb availability and accumulation in the vegetable and more biofilm-producing bacteria, polysaccharide and protein production, and Pb-immobilizing related gene abundances in the Pb-contaminated soil.

Non-doped and transition metal-doped CuO nano-powders: structure-physical properties and anti-adhesion activity relationship

Bacterial contamination and biofilm formation generate severe problems in many fields. Among these biofilm-forming bacteria, Staphylococcus epidermidis (S. epidermidis) has emerged as a major cause of nosocomial infection (NI). However, with the dramatic rise in resistance toward conventional antibiotics, there is a pressing need for developing effective anti-biofilms. So, fabrication of copper oxide nanoparticles (NPs) is one of the new strategies to combat biofilms. Notably, doped CuO NPs in anti-biofilm therapy have become a hot spot of attention in recent years due to their physicochemical properties. In this context, the present work deals with the investigation of undoped and transition metal (TM)-doped CuO NPs (TM = Zn, Ni, Mn, Fe and Co), synthesized via the co-precipitation method. The synthesized CuO NPs are characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Results consistently revealed the successful formation of CuO NPs using the co-precipitation method and confirmed that TM ions are successfully inserted into CuO crystal lattice. We found that doping changes the morphology of the CuO NPs and increases their crystallite size. The XPS results show a non-uniform distribution of the doping concentration, with a depletion or an enrichment of the NP surface depending on the element considered. Furthermore, the anti-adhesive potential of CuO NPs against S. epidermidis S61 biofilm formation is evaluated in this study by crystal violet and fluorescence microscopy assays. All synthesized NPs exhibit considerable anti-adhesive activity against S. epidermidis S61 biofilm. Interestingly, compared to undoped CuO, Fe and Ni-doped oxides show an improved activity when used at high concentrations, whereas Mn-doped CuO is the most efficient at low concentrations. This makes TM-doped CuO a promising candidate to be used in biomedical applications.

Bacterial contamination and biofilm formation generate severe problems in many fields.

Environmental Biofilms as Reservoirs for Antimicrobial Resistance

Characterizing the response of microbial communities to a range of antibiotic concentrations is one of the strategies used to understand the impact of antibiotic resistance. Many studies have described the occurrence and prevalence of antibiotic resistance in microbial communities from reservoirs such as hospitals, sewage, and farm feedlots, where bacteria are often exposed to high and/or constant concentrations of antibiotics. Outside of these sources, antibiotics generally occur at lower, sub-minimum inhibitory concentrations (sub-MICs). The constant exposure to low concentrations of antibiotics may serve as a chemical "cue" that drives development of antibiotic resistance. Low concentrations of antibiotics have not yet been broadly described in reservoirs outside of the aforementioned environments, nor is the transfer and dissemination of antibiotic resistant bacteria and genes within natural microbial communities fully understood. This review will thus focus on low antibiotic-concentration environmental reservoirs and mechanisms that are important in the dissemination of antibiotic resistance to help identify key knowledge gaps concerning the environmental resistome.