Inhibiting P. fluorescens biofilms with fluoropolymer-embedded silver nanoparticles: an in-situ spectroscopic study

Development of super nanoantimicrobials combining AgCl, tetracycline and benzalkonium chloride

In this work, we demonstrate that a simple argentometric titration is a scalable, fast, green and robust approach for producing AgCl/antibiotic hybrid antimicrobial materials. We titrated AgNO3 into tetracycline hydrochloride (TCH) aqueous solution, thus forming AgCl/TCH in a one-step procedure. Furthermore, we investigated the one-pot synthesis of triply synergistic super-nanoantimicrobials, combining an inorganic source of Ag+ ions (AgCl), a disinfecting agent (benzyl-dimethyl-hexadecyl-ammonium chloride, BAC) and a molecular antibiotic (tetracycline hydrochloride, TCH). Conventional antimicrobial tests, industrial biofilm detection protocols, and in situ IR-ATR microbial biofilm monitoring, have been adapted to understand the performance of the synthesized super-nanoantimicrobial. The resulting hybrid AgCl/BAC/TCH nanoantimicrobials are found to be synergistically active in eradicating Salmonella enterica and Lentilactobacillus parabuchneri bacteria and biofilms. This study paves the way for the development of a new class of super-efficient nanoantimicrobials that combine relatively low amounts of multiple active species into a single (nano)formulation, thus preventing the development of antimicrobial resistance towards a single active principle.

Fluorocarbon Plasma-Polymerized Layer Increases the Release Time of Silver Ions and the Antibacterial Activity of Silver-Based Coatings

Silver-based antibacterial coatings limit the spread of hospital-acquired infections. Indeed, the use of silver and silver oxide nanoparticles (Ag and AgO NPs) incorporated in amorphous hydrogenated carbon (a-C:H) as a matrix demonstrates a promising approach to reduce microbial contamination on environmental surfaces. However, its success as an antibacterial coating hinges on the control of Ag+ release. In this sense, if a continuous release is required, an additional barrier is needed to extend the release time of Ag+. Thus, this research investigated the use of a plasma fluoropolymer (CFx) as an additional top layer to elongate Ag+ release and increase the antibacterial activity due to its high hydrophobic nature. Herein, a porous CFx film was deposited on a-C:H containing Ag and AgO NPs using pulsed afterglow low pressure plasma polymerization. The chemical composition, surface wettability and morphology, release profile, and antibacterial activity were analyzed. Overall, the combination of a-C:H:Ag (12.1 at. % of Ag) and CFx film (120.0°, F/C = 0.8) successfully inactivated 88% of E. coli and delayed biofilm formation after 12 h. Thus, using a hybrid approach composed of Ag NPs and a hydrophobic polymeric layer, it was possible to increase the overall antibacterial activity of the coating.

Rapid discrimination of Lentilactobacillus parabuchneri biofilms via in situ infrared spectroscopy

Microbial contamination in food industry is a source of foodborne illnesses and biofilm-related diseases. In particular, biogenic amines (BAs) accumulated in fermented foods via lactic acid bacterial activity exert toxic effects on human health. Among these, biofilms of histamine-producer Lentilactobacillus parabuchneri strains adherent at food processing equipment surfaces can cause food spoilage and poisoning. Understanding the chain of contamination is closely related to elucidating molecular mechanisms of biofilm formation. In the present study, an innovative approach using integrated chemical sensing technologies is demonstrated to fundamentally understand the temporal behavior of biofilms at the molecular level by combining mid-infrared (MIR) spectroscopy and fluorescence sensing strategies. Using these concepts, the biofilm forming capacity of six cheese-isolated L. parabuchneri strains (IPLA 11151, 11150, 11129, 11125, 11122 and 11117) was examined. The cut-off values for the biofilm production ability of each strain were quantified using crystal violet (CV) assays. Real-time infrared attenuated total reflection spectroscopy (IR-ATR) combined with fluorescence quenching oxygen sensing provides insight into distinct molecular mechanisms for each strain. IR spectra showed significant changes in characteristic bands of amides, lactate, nucleic acids, and extracellular polymeric substances (i.e., lipopolysaccharides, phospholipids, phosphodiester, peptidoglycan, etc.), which are major contributors to biofilm maturation involved in the initial adhesion processes. Chemometric methods including principal component analysis and partial least square-discriminant analysis facilitated the rapid determination and classification of cheese isolated L. parabuchneri strains unambiguously differentiating the IR signatures based on their ability to produce biofilm. All biofilms were morphologically characterized by confocal laser scanning microscopy on relevant industrial equipment surfaces. In summary, this innovative approach combining MIR spectroscopy with luminescence sensing enables real-time insight into the molecular composition and formation of L. parabuchneri biofilms.

Thin-Film Waveguide Laser Spectroscopy: A Novel Platform for Bacterial Analysis

Bacterial sensing based on quantum cascade laser spectroscopy coupled with diamond or gallium arsenide thin-film waveguides is a novel analytical tool for gaining high-resolution infrared spectroscopic information of planktonic and sessile bacteria, as shown in the present study for Escherichia coli. During observation periods of up to 24 h, diamond and gallium arsenide thin-film waveguide laser spectroscopy was compared to information obtained via conventional Fourier transform infrared spectroscopy. The proliferation behavior of E. coli at those surfaces was complementarily investigated using atomic force microscopy and scanning electron microscopy.

Preparation of Laser-Ablated Ag Nanoparticle-MMT Clay-Based Beeswax Antibiofilm Coating

Unlike other antimicrobial agents, Ag-based composites are stable and currently widely used as broad spectral additives, fighting microbial biofilms and other biological threats. The goal of the present study is to develop a green, multifunctional, and robust antibiofilm water-insoluble coating, inhibiting histamine-producing Lentilactobacillus parabuchneri biofilms. Herein, laser-ablated Ag NPs (L-Ag NPs) were incorporated into and onto a montmorillonite (MMT) surface layer with a simple wet chemical method, provided that the electrostatic interaction between L-Ag NPs and MMT clay led to the formation of L-Ag/MMT nanoantimicrobials (NAMs). The use of MMT support can facilitate handling Ag NPs in industrial applications. The Ag/MMT composite was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which confirmed the entrapment of L-Ag NPs into MMT clay. The surface chemical composition was assessed with X-ray photoelectron spectroscopy, proving that Ag NPs were in contact with and deposited onto the surface of MMT. The characteristic L-Ag/MMT band was investigated with UV-vis spectroscopy. Following that, the L-Ag/MMT composite was embedded into a biosafe water-insoluble beeswax agent with a spin coating technique. The antimicrobial ion release kinetic profile of the L-Ag/MMT/beeswax coating through an electrothermal atomic absorption spectroscopy (ETAAS) study supported the controlled release of Ag ions, reaching a plateau at 420 ± 80 nM, which is safe from the point of view of Ag toxicity. Microbial biofilm growth inhibition was assessed with real-time in situ Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) in a flow cell assembly over 32 h. The study was further supported by optical density (OD) measurements and SEM on bacteria incubated in the presence of the L-Ag/MMT/beeswax coating.

Antimicrobial Efficiency of Chitosan and Its Methylated Derivative against Lentilactobacillus parabuchneri Biofilms

Antimicrobial materials are considered potential alternatives to prevent the development of biofilm-associated contaminations. Concerns regarding synthetic preservatives necessitate the development of innovative and safe natural antimicrobials. In the present study, we discuss the in situ infrared attenuated total reflection spectroscopy (IR-ATR) investigations of the selective antimicrobial efficiency of chitosan in controlling the growth of Lentilactobacillus parabuchneri biofilms. The protonated charges of chitosan were additionally amplified by structural modification via methylation, yielding quaternized derivative TMC (i.e., N, N, N-trimethyl chitosan). To evaluate antimicrobial effectiveness against L. parab. biofilms, IR-ATR spectroscopy provided information on molecular mechanisms and insights into chemical changes during real-time biofilm inhibition studies. The integrated fiberoptic oxygen microsensors enabled monitoring oxygen (O₂) concentration gradients within biofilms, thereby confirming the metabolic oxygen depletion dropping from 4.5 to 0.7 mg L^-1. IR studies revealed strong electrostatic interactions between chitosan/its water-soluble derivative and bacteria, indicating that a few hours were sufficient to affect biofilm disruption. The significant decrease in the IR bands is related to the characteristic spectral information of amide I, II, III, nucleic acid, and extracellular polymeric matrix (EPS) produced by L. parabuchneri biofilms. Cell clusters of biofilms, microcolonies, and destabilization of the EPS matrix after the addition of biopolymers were visualized using optical microscopy. In addition, scanning electron microscopy (SEM) of biofilms grown on polystyrene and stainless-steel surfaces was used to examine morphological changes, indicating the disintegration of the biofilm matrix into individual cells. Quantification of the total biofilm formation correlated with the CV assay results, indicating cell death and lysis. The electrostatic interactions between chitosan and the bacterial cell wall typically occur between protonated amino groups and negatively charged phospholipids, which promote permeabilization. Biofilm growth inhibition was assessed by a viability assay for a period of 72 h and in the range of low MIC values (varying 0.01-2%). These results support the potential of chitosan and TMC for bacterial growth prevention of the foodborne contaminant L. parabuchneri in the dairy industry and for further implementation in food packaging.

Atomic force and infrared spectroscopic studies on the role of surface charge for the anti-biofouling properties of polydopamine films

Antibacterial polymer materials have gained interest due to their capability to inhibit or eradicate biofilms with greater efficiency in comparison with their monomeric counterparts. Among the antimicrobial and anti-biofouling polymers, catecholamine-based polymers - and in particular polydopamine - have been studied due to their favorable adhesion properties, which can be tuned by controlling the pH value. In this study, we used atomic force microscopy (AFM)-based spectroscopy to investigate the relation between the adhesion properties and surface charge density and the pH of electrochemically deposited polydopamine films presenting a dissociation constant of polydopamine of 6.3 ± 0.2 and a point of zero charge of 5.37 ± 0.06. Furthermore, using AFM and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), the influence of the surface charge density of polydopamine on bacterial adhesion and biofilm formation was investigated. It was shown that the adhesion of Escherichia coli at positively charged polydopamine is three times higher compared to a negatively charged polymer, and that the formation of biofilms is favored at positively charged polymers.

Green Synthesis and Characterization of Antimicrobial Synergistic AgCl/BAC Nanocolloids

All over the world, one of the major challenges is the green synthesis of potential materials against antimicrobial resistance and viruses. This study demonstrates a simple method like chemistry lab titration to synthesize green, facile, scalable, reproducible, and stable synergistic silver chloride/benzyldimethylhexadecyl-ammonium chloride (AgCl/BAC) colloidal Nanoantimicrobials (NAMs). Nanocolloidal dispersions of AgCl in an aqueous medium are prepared by using silver nitrate (AgNO₃) as precursor and BAC as both sources of chloride and stabilizer, holding an asymmetric molecular structure. The synthetic approach is scalable and green. Both the morphology and stability of AgCl/BAC nanocolloids (NCs) were investigated as a function of different molar fractions of the reagents. AgCl/BAC NCs were characterized by transmission electron microscopy (TEM) and X-ray photoelectron and UV–vis spectroscopies. Zeta potential measurements revealed increasing positive potential values at every stage of the synthesis. Size distribution and hydrodynamic diameter of the particles were measured by dynamic light scattering (DLS), which predicted the formation of BAC layered structures associated with the AgCl nanoparticles (NPs). Small-angle X-ray scattering (SAXS) experiments verify the thickness of the BAC bilayer around AgCl. The produced AgCl/BAC NCs probably have synergistic antimicrobial properties from the AgCl core and the biocide BAC shell. AgCl/BAC NCs stability over months was investigated. The experimental evidence supports the morphological stability of the AgCl/BAC NCs, while higher positive zeta potential values anticipate a long-term antimicrobial effect: a higher surface charge causes NPs to be potentially more lethal to bacteria. AgCl/BAC antimicrobial aqueous colloidal suspensions will be used as additives for the industrial production of antimicrobial coatings.

Potential of Nanoparticles Integrated with Antibacterial Properties in Preventing Biofilm and Antibiotic Resistance

Nanotechnology has become an emerging technology in the medical field and is widely applicable for various clinical applications. The potential use of nanoparticles as antimicrobial agents is greatly explored and taken into consideration as alternative methods to overcome the challenges faced by healthcare workers and patients in preventing infections caused by pathogenic microorganisms. Among microorganisms, bacterial infections remain a major hurdle and are responsible for high morbidity and mortality globally, especially involving those with medical conditions and elderly populations. Over time, these groups are more vulnerable to developing resistance to antibiotics, as bacterial biofilms are difficult to destroy or eliminate via antibiotics; thus, treatment becomes unsuccessful or ineffective. Mostly, bacterial biofilms and other microbes can be found on medical devices and wounds where they disperse their contents which cause infections. To inhibit biofilm formations and overcome antibiotic resistance, antimicrobial-loaded nanoparticles alone or combined with other substances could enhance the bactericidal activity of nanomaterials. This includes killing the pathogens effectively without harming other cells or causing any adverse effects to living cells. This review summarises the mechanisms of actions employed by the different types of nanoparticles which counteract infectious agents in reducing biofilm formation and improve antibiotic therapy for clinical usage.

The Effect of Haematocrit on Measurement of the Mid-Infrared Refractive Index of Plasma in Whole Blood

Recent advances suggest that miniaturised mid-infrared (MIR) devices could replace more time-consuming, laboratory-based techniques for clinical diagnostics. This work uses Fourier transform infrared spectroscopy to show that the MIR complex refractive index of whole blood varies across a range of haematocrit. This indicates that the use of an evanescent measurement is not sufficient to optically exclude the cellular content of blood in the MIR, as previously assumed. Here, spectral refractive index data is presented in two ways. First, it is given as whole blood with varying haematocrit. Second, it is given as the percentage error that haematocrit introduces to plasma. The maximum error in the effective plasma refractive index due to the haematocrit of healthy adults was 0.25% for the real part n and 11% for the imaginary part k. This implies that calibration measurements of haematocrit can be used to account for errors introduced by the cellular content, enabling plasma spectra and analyte concentrations to be indirectly calculated from a whole blood sample. This methodological advance is of clinical importance as plasma concentration of analytes such as drugs can be determined using MIR without the preprocessing of whole blood.

Green Synthesis and Characterization of Carboxymethyl Cellulose Fabricated Silver-Based Nanocomposite for Various Therapeutic Applications

Purpose

The current study proposed the simple, eco-friendly and cost-effective synthesis of carboxymethyl cellulose (CMC) structured silver-based nanocomposite (CMC-AgNPs) using Syzygium aromaticum buds extract.

Methods

The CMC-AgNPs were characterized by ultraviolet (UV) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transmission infra-red (FTIR), energy-dispersive X-ray (EDX), and dynamic light scattering (DLS) techniques. The synthesized nanocomposites were evaluated for their bactericidal kinetics, in-vivo anti-inflammatory, anti-leishmaniasis, antioxidant and cytotoxic activities using different in-vitro and in-vivo models.

Results

The spherical shape nanocomposite of CMC-AgNPs was synthesized with the mean size range of 20–30 nm, and the average pore diameter is 18.2 nm while the mean zeta potential of −31.6 ± 3.64 mV. The highly significant (P < 0.005) antibacterial activity was found against six bacterial strains with the ZIs of 24.6 to 27.9 mm. More drop counts were observed in Gram-negative strains after 10 min exposure with CMC-AgNPs. Significant damage in bacterial cell membrane was also observed in atomic force microscopy (AFM) after treated with CMC-AgNPs. Nanocomposite showed highly significant anti-inflammatory activity in cotton pellet induced granuloma model (Phase I) in rats with the mean inhibitions of 43.13% and 48.68% at the doses of 0.025 and 0.05 mg/kg, respectively, when compared to control. Reduction in rat paw edema (Phase II) was also highly significant (0.025 mg/kg; 42.39%; 0.05 mg/kg, 47.82%). At dose of 0.05 mg/kg, CMC-AgNPs caused highly significant decrease in leukocyte counts (922 ± 83), levels of CRP (8.4 ± 0.73 mg/mL), IL-1 (177.4 ± 21.3 pg/mL), IL-2 (83.7 ± 11.5 pg/mL), IL-6 (83.7 ± 11.5 pg/mL) and TNF-α (18.3 ± 5.3 pg/mL) as compared to control group. CMC-AgNPs produced highly effective anti-leishmaniasis activity with the viable Leishmania major counts decreased up to 36.7% within 24 h, and the IC₅₀ was found to be 28.41 μg/mL. The potent DPPH radical scavenging potential was also observed for CMC-AgNPs with the IC₅₀ value of 112 μg/mL. Furthermore, the cytotoxicity was assessed using HeLa cell lines with the LC₅₀ of 108.2 μg/mL.

Conclusion

The current findings demonstrate positive attributes of CMC fabricated AgNPs as a promising antibacterial, anti-inflammatory, anti-leishmaniasis, and antioxidant agent with low cytotoxic potential.

Surface plasmonic resonance tunable nanocomposite thin films applicable to color filters, heat mirrors, semi-transparent electrodes, and electromagnetic-shields

This study proposes a plasmonic resonance-tunable nanocomposite thin film, which applies to a color filter, heat mirror, semi-transparent color electrode, and electromagnetic shield, given that the size and structure of nanoclusters can be controlled by a sputtering power density. The structural and functional properties of silver/plasma-polymer-fluorocarbon (Ag/PPFC) nanocomposite thin films, which were sputtered by ternary composite targets, were investigated with various compositions and sputtering power densities. The growth of Ag nanoclusters of the thin film was suppressed as the sputtering power density increased due to the rich functional group of -CF_x- fluorine. As a result, a continuous color change from blue to yellow could be expressed on films given the precise control of the surface plasmonic resonance phenomenon. Grazing-incidence small-angle scattering (GISAXS) analysis indicated that the sputtering power density had a significant effect on the size, distribution, and orientation of the Ag nanoclusters in the thin film. For low sputtering power densities, Ag nanoclusters were forming aggregations along the out-of-plane direction, but as the sputtering power density increased, the nanoclusters showed random distribution instead of large aggregates. We also demonstrated applications of Ag/PPFC nanocomposite thin films to a color filter, heat mirror, semi-transparent electrode, and electromagnetic shield. In addition, the fabrication of a large-area film (400 × 700 mm²) showed that the approach applies highly to industries.

Mussel-inspired antimicrobial coating on PTFE barrier membranes for guided tissue regeneration

Guided tissue regeneration procedures to treat periodontitis lesions making use of polytetrafluoroethylene (PTFE) membranes exhibit large variability in their surgical outcomes, due to bacterial infection following implantation. This work reports on a facile method to obtain antimicrobial coatings for such PTFE membranes, by exploiting a mussel-inspired approach andin-situformation of silver nanoparticles (AgNPs). PTFE films were initially coated with self-polymerized 3,4-dihydroxy-DL-phenylalanine (DOPA) (PTFE-DOPA), then incubated with AgNO₃solution. In the presence of catechol moieties, Ag⁺ions reduced into Ag⁰, forming AgNPs of around 68 nm in the polyDOPA coating on PTFE membranes (PTFE-DOPA-Ag). The x-ray photoelectron spectroscopy, atomic force microscopy and scanning electron microscopy analyses indicated that the AgNPs were distributed quite homogeneously in the polymeric membrane. The antimicrobial ability of PTFE-DOPA-Ag membranes againstStaphylococcus aureusandEscherichia coliwas assessed.In vitrocell assay using NIH 3T3 fibroblasts showed that, although cells were adhered to PTFE-DOPA-Ag membranes, their viability and proliferation were limited demonstrating again the antibacterial activities of PTFE-DOPA-Ag membranes. This work provides proof-of-concept study of a new versatile approach for AgNPs coating, which may be easily applied to many other types of polymeric or metallic implants through exploiting the adhesive behavior of mussel-inspired coatings.

Personalized Reusable Face Masks with Smart Nano-Assisted Destruction of Pathogens for COVID-19: A Visionary Road

The Coronavirus disease 2019 (COVID-19) emergency has demonstrated that the utilization of face masks plays a critical role in limiting the outbreak. Healthcare professionals utilize masks all day long without replacing them very frequently, thus representing a source of cross-infection for patients and themselves. Nanotechnology is a powerful tool with the capability to produce nanomaterials with unique physicochemical and antipathogen properties. Here, how to realize non-disposable and highly comfortable respirators with light-triggered self-disinfection ability by bridging bioactive nanofiber properties and stimuli-responsive nanomaterials is outlined. The visionary road highlighted in this Concept is based on the possibility of developing a new generation of masks based on multifunctional membranes where the presence of nanoclusters and plasmonic nanoparticles arranged in a hierarchical structure enables the realization of a chemically driven and on-demand antipathogen activities. Multilayer electrospun membranes have the ability to dissipate humidity present within the mask, enhancing the wearability and usability. The photothermal disinfected membrane is the core of these 3D printed and reusable masks with moisture pump capability. Personalized face masks with smart nano-assisted destruction of pathogens will bring enormous advantages to the entire global community, especially for front-line personnel, and will open up great opportunities for innovative medical applications.

Physics Comes to the Aid of Medicine-Clinically-Relevant Microorganisms through the Eyes of Atomic Force Microscope

Despite the hope that was raised with the implementation of antibiotics to the treatment of infections in medical practice, the initial enthusiasm has substantially faded due to increasing drug resistance in pathogenic microorganisms. Therefore, there is a need for novel analytical and diagnostic methods in order to extend our knowledge regarding the mode of action of the conventional and novel antimicrobial agents from a perspective of single microbial cells as well as their communities growing in infected sites, i.e., biofilms. In recent years, atomic force microscopy (AFM) has been mostly used to study different aspects of the pathophysiology of noninfectious conditions with attempts to characterize morphological and rheological properties of tissues, individual mammalian cells as well as their organelles and extracellular matrix, and cells’ mechanical changes upon exposure to different stimuli. At the same time, an ever-growing number of studies have demonstrated AFM as a valuable approach in studying microorganisms in regard to changes in their morphology and nanomechanical properties, e.g., stiffness in response to antimicrobial treatment or interaction with a substrate as well as the mechanisms behind their virulence. This review summarizes recent developments and the authors’ point of view on AFM-based evaluation of microorganisms’ response to applied antimicrobial treatment within a group of selected bacteria, fungi, and viruses. The AFM potential in development of modern diagnostic and therapeutic methods for combating of infections caused by drug-resistant bacterial strains is also discussed.

Cu Nanoparticle-Loaded Nanovesicles with Antibiofilm Properties. Part I: Synthesis of New Hybrid Nanostructures

Copper nanoparticles (CuNPs) stabilized by quaternary ammonium salts are well known as antimicrobial agents. The aim of this work was to study the feasibility of the inclusion of CuNPs in nanovesicular systems. Liposomes are nanovesicles (NVs) made with phospholipids and are traditionally used as delivery vehicles because phospholipids favor cellular uptake. Their capacity for hydrophilic/hydrophobic balance and carrier capacity could be advantageous to prepare novel hybrid nanostructures based on metal NPs (Me-NPs). In this work, NVs were loaded with CuNPs, which have been reported to have a biofilm inhibition effect. These hybrid materials could improve the effect of conventional antibacterial agents. CuNPs were electro-synthesized by the sacrificial anode electrolysis technique in organic media and characterized in terms of morphology through transmission electron microscopy (TEM). The NVs were prepared by the thin film hydration method in aqueous media, using phosphatidylcholine (PC) and cholesterol as a membrane stabilizer. The nanohybrid systems were purified to remove non-encapsulated NPs. The size distribution, morphology and stability of the NV systems were studied. Different quaternary ammonium salts in vesicular systems made of PC were tested as stabilizing surfactants for the synthesis and inclusion of CuNPs. The entrapment of charged metal NPs was demonstrated. NPs attached preferably to the membrane, probably due to the attraction of their hydrophobic shell to the phospholipid bilayers. The high affinity between benzyl-dimethyl-hexadecyl-ammonium chloride (BDHAC) and PC allowed us to obtain stable hybrid NVs c.a. 700 nm in diameter. The stability of liposomes increased with NP loading, suggesting a charge-stabilization effect in a novel antibiofilm nanohybrid material.

Scanning electrochemical microscopy and its potential for studying biofilms and antimicrobial coatings

Biofilms are known to be well-organized microbial communities embedded in an extracellular polymeric matrix, which supplies bacterial protection against external stressors. Biofilms are widespread and diverse, and despite the considerable large number of publications and efforts reported regarding composition, structure and cell-to-cell communication within biofilms in the last decades, the mechanisms of biofilm formation, the interaction and communication between bacteria are still not fully understood. This knowledge is required to understand why biofilms form and how we can combat them or how we can take advantage of these sessile communities, e.g. in biofuel cells. Therefore, in situ and real-time monitoring of nutrients, metabolites and quorum sensing molecules is of high importance, which may help to fill that knowledge gap. This review focuses on the potential of scanning electrochemical microscopy (SECM) as a versatile method for in situ studies providing temporal and lateral resolution in order to elucidate cell-to-cell communication, microbial metabolism and antimicrobial impact, e.g. of antimicrobial coatings through the study of electrochemical active molecules. Given the complexity and diversity of biofilms, challenges and limitations will be also discussed.

Testing Anti-Biofilm Polymeric Surfaces: Where to Start?

Present day awareness of biofilm colonization on polymeric surfaces has prompted the scientific community to develop an ever-increasing number of new materials with anti-biofilm features. However, compared to the large amount of work put into discovering potent biofilm inhibitors, only a small number of papers deal with their validation, a critical step in the translation of research into practical applications. This is due to the lack of standardized testing methods and/or of well-controlled in vivo studies that show biofilm prevention on polymeric surfaces; furthermore, there has been little correlation with the reduced incidence of material deterioration. Here an overview of the most common methods for studying biofilms and for testing the anti-biofilm properties of new surfaces is provided.

Cyclic Changes in the Amide Bands Within Escherichia coli Biofilms Monitored Using Real-Time Infrared Attenuated Total Reflection Spectroscopy (IR-ATR)

Contrary to the planktonic state of bacteria, their biofilm form represents severe complications in areas such as human medicine or food industry due to the increasing resistance against harsh conditions and treatment. In the present study, infrared attenuated total reflection (IR-ATR) spectroscopy has been applied as an analytic tool studying Escherichia coli ( E. coli) biofilm formation close to real time. We report on IR spectroscopic investigations on the biofilm formation via ATR waveguides probing the biofilm in the spectral window of 1800-900 cm^-1 at dynamic flow conditions, which facilitated monitoring the growth dynamics during several days. Key IR bands are in the range 1700-1590 cm^-1 (amide I), 1580-1490 cm^-1 (amide II), and 1141-1006 cm^-1 extracellular polymeric substances (EPS), which were evaluated as a function of time. Cyclic fluctuations of the amide I and amide II bands and a continuous increase of the EPS band were related to the starvation of bottom-layered bacteria caused by the nutrient gradient. Potential death of bacteria may then result in cannibalistic behavior known for E. coli colonies. Observing this behavior via IR spectroscopy allows revealing these cyclical changes in bottom-layered bacteria within the biofilm under continuous nutrient flow, in molecular detail, and during extended periods for the first time.

Electrospun Nanomaterials Implementing Antibacterial Inorganic Nanophases

Electrospinning is a versatile, simple, and low cost process for the controlled production of fibers. In recent years, its application to the development of multifunctional materials has encountered increasing success. In this paper, we briefly overview the general aspects of electrospinning and then we focus on the implementation of inorganic nanoantimicrobials, e.g., nanosized antimicrobial agents in electrospun fibers. The most relevant characteristics sought in nanoantimicrobials supported on (or dispersed into) polymeric materials are concisely discussed as well. The interesting literature issued in the last decade in the field of antimicrobial electrospun nanomaterials is critically described. A classification of the most relevant studies as a function of the different approaches chosen for incorporating nanoantimicrobials in the final material is also provided.

Identification of natural product compounds as quorum sensing inhibitors in Pseudomonas fluorescens P07 through virtual screening

Pseudomonas fluorescens, a Gram-negative psychrotrophic bacteria, is the main microorganism causing spoilage of chilled raw milk and aquatic products. Quorum sensing (QS) widely exists in bacteria to monitor their population densities and regulate numerous physiological activities, such as the secretion of siderophores, swarming motility and biofilm formation. Thus, searching for quorum sensing inhibitors (QSIs) may be another promising way to control the deterioration of food caused by P. fluorescens. Here, we screened a traditional Chinese medicine (TCM) database to discover potential QSIs with lesser toxicity. The gene sequences of LuxI- and LuxR-type proteins of P. fluorescens P07 were obtained through whole-genome sequencing. In addition, the protein structures built by homology modelling were used as targets to screen for QSIs. Twenty-one compounds with a dock score greater than 6 were purchased and tested by biosensor strains (Chromobacterium violaceum CV026 and Agrobacterium tumefaciens A136). The results showed that 10 of the compounds were determined as hits (hit rate: 66.67%). Benzyl alcohol, rhodinyl formate and houttuynine were effective QSIs. The impact of the most active compound (benzyl alcohol) on the phenotypes of P. fluorescens P07, including swimming and swarming motility, production of extracellular enzymes and siderophores, N-acylhomoserine lactone (AHLs) content and biofilm formation were determined. The inhibitory mechanism of benzyl alcohol on the QS system of P. fluorescens P07 is further discussed. This study reveals the feasibility of searching for novel QSIs through virtual screening.

In vitroantibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: II. Fourier transform infrared spectroscopy

The metabolic response of Gram-positiveStaphylococcus epidermidisbacteria to bioceramic substrates was probed by Fourier transform infrared spectroscopy.