Bacteria-surface interactions

Investigation of the susceptibility of clinical infection loads to nitric oxide antibacterial treatment

The persistent infection of medical devices by opportunistic pathogens has led to the development of antimicrobial medical device polymers. Nitric oxide (NO) is an endogenous antimicrobial molecule that is released through the degradation of synthetic donor molecules such as S-nitroso-N-acetylpenicillamine (SNAP) embedded into polymer membranes. It is hypothesized that the clinical success of these polymers is enhanced by the physiological release of NO and the consequent prevention of infection. However, such NO-releasing materials have never been evaluated against microbial loads that are commensurate with clinical infection levels. This study aimed to develop a standardized polymer film impregnated with SNAP that consistently releases NO and evaluates its efficacy against bacterial loads that represent clinical infection parameters. Microbial loads of 103, 105, and 108 (colony-forming units) CFU mL-1 were exposed to the NO-releasing polymer, corresponding to bloodstream infections, catheter-associated urinary tract infections, and standard laboratory exposure levels that have been reported in the scientific literature. By 24 h, SNAP films led to >1 log reduction of adhered and viable E. coli at all tested microbial loads compared to control polydimethylsiloxane (PDMS). Further, SNAP films displayed no viable adhered S. aureus at the 103 microbial level for the entire study and showed total planktonic killing by 8 h. NO localization within bacterial cells adhering to the films was evaluated, revealing higher NO uptake and consequent bacterial killing by SNAP samples. This unique study shows that NO-releasing polymers not only kill bacteria adhered to the polymer surface, but localized delivery leads to environmental planktonic bacterial killing that prevents adhesion from occurring. Furthermore, the promising findings of NO-releasing polymers in scientific research indicate their potential for successful application in clinical settings to prevent infections.

Layer-by-layer coated probiotics with tannic acid-Ca2+ and casein phosphopeptide complexes for caries prevention and enamel remineralization

Dental caries is a common disease resulting from tooth demineralization caused by bacterial plaque. Probiotics have shown great potential against caries by regulating the balance of oral flora. However, obstacles such as poor colonization and lysozyme sensitivity in oral cavity hinder their further application. In this study, an efficient layer-by-layer surface coating of tannic acid (TA)-Ca2+ and casein phosphopeptide (CPP) was applied to the probiotic Bifidobacterium infantis (BI) with potential anti-caries activity. Multi-functionalized probiotics thus prepared (called BI@TA-Ca2+@CPP) exhibited similar growth pattern, resistance to lysozyme and enhanced colonization potential. The ability of BI@TA-Ca2+@CPP in inhibiting cariogenic biofilm formation was improved. Moreover, BI@TA-Ca2+@CPP showed excellent remineralization efficacy. In a caries-induced rat model, BI@TA-Ca2+@CPP significantly prevented the occurrence and progression of tooth decay, meanwhile showing good biocompatibility. In summary, this study underlines the importance of probiotics coating in antibiofilm and remineralization activity as a promising strategy against dental caries.

Improving the bioactivity of cellulose acetate hemodialysis membranes through nanosilver modification

The effectiveness and safety of hemodialysis can be hindered by protein accumulation, mechanical instability of membranes and bacterial infection during the dialytic therapy. Herein, we show that cellulose acetate membranes modified with the low-fouling polymers (namely polyvinylpyrrolidone and polyethylene glycol), followed by the in situ reduction of different densities of silver oxide(I) nanoparticles, can effectively address these limitations. These improvements comprise the enhanced resistance to the protein fouling, improved antimicrobial capabilities against S. aureus, increased selectivity, and thermal stability and mechanical strength. The nano-enhanced membranes showed an improved albumin rejection rate of approximately 90 %, and the creatinine clearance rate ranged between 90 and 94 %. Our findings demonstrate that nanosilver-modified membranes can be readily prepared from precursor solutions to act as robust, biocompatible, and hydrophilic hemodialysis membranes with controlled bacteriostatic potential, antifouling properties and high toxin clearance.

Graveyard effects of antimicrobial nanostructured titanium over prolonged exposure to drug resistant bacteria and fungi

Innovations in nanostructured surfaces have found a practical place in the medical area with use in implant materials for post-operative infection prevention. These textured surfaces should be dual purpose: (1) bactericidal on contact and (2) resistant to biofilm formation over prolonged periods. Here, hydrothermally etched titanium surfaces were tested against two highly antimicrobial resistant microbial species, methicillin-resistant Staphylococcus aureus and Candida albicans. Two surface types - unmodified titanium and nanostructured titanium - were incubated in a suspension of each microbial strain for 1 day and 7 days. Surface topography and cross-sectional information of the microbial cells adhered to the surfaces, along with biomass volume and live/dead rate, showed that while nanostructured titanium was able to kill microbes after 1 day of exposure, after 7 days, the rate of death becomes negligible when compared to the unmodified titanium. This suggests that as biofilms mature on a nanostructured surface, the cells that have lysed conceal the nanostructures and prime the surface for planktonic cells to adhere, decreasing the possibility of structure-induced lysis. Synchrotron macro-attenuated total reflection Fourier transform infrared (macro ATR-FTIR) micro-spectroscopy was used to elucidate the biochemical changes occurring following exposure to differing surface texture and incubation duration, providing further understanding into the effects of surface morphology on the biochemical molecules (lipids, proteins and polysaccharides) in an evolving and growing microbial colony.

Programming Surface Motility and Modulating Physiological Behaviors of Bacteria via Biosurfactant-Mimetic Polyurethanes

Modulating microbial motility and physiology can enhance the production of bacterial macromolecules and small molecules. Herein, a platform of water-soluble and amphiphilic peptidomimetic polyurethanes is reported as a means of regulating bacterial surface behavior and the concomitant production of extracellular polymeric substances (EPS). It is demonstrated that carboxyl (-COOH)-containing polyurethanes exhibited 17-fold and 80-fold enhancements in Pseudomonas aeruginosa (P. aeruginosa) swarming and twitching areas, respectively. Conversely, an amine (-NH2)-functionalized polyurethane reduces the P. aeruginosa swarming area by 58%. Similar influences on the surface motility of Escherichia coli (E. coli) and a nonswarming P. aeruginosa mutant strain are also observed. Notably, -COOH polyurethanes completely wet the agar hydrogel surface and promote bacterial surface proliferation, resulting in enhanced EPS and rhamnolipid production. The programming of bacterial spatial migration into designed patterns is achieved by leveraging the opposing influences of -NH2 and -COOH polyurethanes. The results highlight the potential of this synthetic polyurethane platform and potentially other polymer systems as an exciting approach to control bacterial surface behaviors and influence the production of engineered living materials.

Antibacterial effects and mechanisms of quercetin-β-cyclodextrin complex mediated photodynamic on Escherichia coli O157:H7

Quercetin is a natural flavonoid with antioxidant, anti-inflammatory, and antibacterial properties. This work aimed to formulate quercetin-cyclodextrin microcapsules (QT-β-CD) while examining their photodynamic antibacterial effects and underlying mechanisms in detail. Characterization of the QT-β-CD was conducted using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The bacteriostatic effects of UV-A irradiation on Escherichia coli O157:H7 (E. coli O157:H7) were investigated. The photodynamic impact of QT-β-CD was assessed by analyzing hydrogen peroxide (H₂O₂) production. The antimicrobial activity was further elucidated through examinations of cell membrane integrity, protein damage, changes in cellular motility, biofilm formation, and extracellular polysaccharide reduction. The effect of QT-β-CD on LuxS and motA gene expression in E. coli O157:H7 was investigated by RT-qPCR. The findings demonstrated that QT-β-CD exhibited potent photodynamic properties and functioned as an efficient photosensitizer, causing substantial damage to E. coli O157:H7 cells. These results underscore the potential of quercetin as an antimicrobial agent for food preservation.

Mesoscale polymer arrays: high aspect ratio surface structures and their digital reconstruction

Inspired by adhesive bio-filamentous structure, such as bacterial pili, this work details the methods used to fabricate and characterize a surface-anchored array of thin, flexible and shape-responsive mesoscale polymer ribbons with a length-to-thickness aspect ratio of up to 100 000. The resulting structures exhibit geometrically complex and dynamic morphologies consistent with elastocapillary bending that experience an increase in curvature over hours of aging due to creep. We develop a computational image analysis framework to generate 3D reconstructions of these densely crowded geometries and extract quantitative descriptors to demonstrate morphological changes due to aging. We demonstrate the robustness of this quantitative method by characterizing the creep-induced change in an aging ribbon array's shape and develop a scaling relationship to describe the importance of ribbon thickness for shape and dynamical observations. These methods demonstrate an essential baseline to probe morphology-property relationships of mesoscale polymer ribbon arrays fabricated from a variety of materials in numerous environments. Through the introduction of perfluorodecalin droplets, we illustrate the potential of these ribbon arrays towards applications in adhesive, microrobotic, and biomedical devices.

Surface roughness influence on extracellular electron microbiologically influenced corrosion of C1018 carbon steel by Desulfovibrio ferrophilus IS5 biofilm

Carbon steel microbiologically influenced corrosion (MIC) by sulfate reducing bacteria (SRB) is known to occur via extracellular electron transfer (EET). A higher biofilm sessile cell count leads to more electrons being harvested for sulfate reduction by SRB in energy production. Metal surface roughness can impact the severity of MIC by SRB because of varied biofilm attachment. C1018 carbon steel coupons (1.2 cm2 top working surface) polished to 36 grit (4.06 μm roughness which is relatively rough) and 600 grit (0.13 μm) were incubated in enriched artificial seawater inoculated with highly corrosive Desulfovibrio ferrophilus IS5 at 28 ℃ for 7 d and 30 d. It was found that after 7 d of SRB incubation, 36 grit coupons had a 11% higher sessile cell count at (2.0 ± 0.17) × 108 cells/cm2, 52% higher weight loss at 22.4 ± 5.9 mg/cm2 (1.48 ± 0.39 mm/a uniform corrosion rate), and 18% higher maximum pit depth at 53 μm compared with 600 grit coupons. However, after 30 d, the differences diminished. Electrochemical tests with transient information supported the weight loss data trends. This work suggests that a rougher surface facilitates initial biofilm establishment but provides no long-term advantage for increased biofilm growth.

Coacervate Dense Phase Displaces Surface-Established Pseudomonas aeruginosa Biofilms

For millions of years, barnacles and mussels have successfully adhered to wet rocks near tide-swept seashores. While the chemistry and mechanics of their underwater adhesives are being thoroughly investigated, an overlooked aspect of marine organismal adhesion is their ability to remove underlying biofilms from rocks and prepare clean surfaces before the deposition of adhesive anchors. Herein, we demonstrate that nonionic, coacervating synthetic polymers that mimic the physicochemical features of marine underwater adhesives remove ∼99% of Pseudomonas aeruginosa (P. aeruginosa) biofilm biomass from underwater surfaces. The efficiency of biofilm removal appears to align with the compositional differences between various bacterial biofilms. In addition, the surface energy influences the ability of the polymer to displace the biofilm, with biofilm removal efficiency decreasing for surfaces with lower surface energies. These synthetic polymers weaken the biofilm-surface interactions and exert shear stress to fracture the biofilms grown on surfaces with diverse surface energies. Since bacterial biofilms are 1000-fold more tolerant to common antimicrobial agents and pose immense health and economic risks, we anticipate that our unconventional approach inspired by marine underwater adhesion will open a new paradigm in creating antibiofilm agents that target the interfacial and viscoelastic properties of established bacterial biofilms.

Nanorod inside hollow-nanosphere structured magnetoelectric nanocatalyst for remotely controlled electrocatalysis assisted environmental remediation

We introduce a highly efficient method for the catalytic breakdown of organic compounds using nanorods embedded within hollow nanospheres structured magnetoelectric nanocatalyst (MENC). MENCs were fabricated through a single-step process utilizing the ultrasonic spray pyrolysis technique. The dynamic electric dipole generation capability due to synergistic interaction between nanorods at the core and the hollow nanosphere shell creates a nanoscale magnetoelectric device capable of electrocatalysis-assisted water purification through advanced oxidation processes under remotely applied magnetic field excitation. Our study examines the electrocatalytic degradation of organic pollutants by MENCs under magnetic field excitation, achieving an unprecedented 90% removal efficiency for synthetic dyes. This remarkable efficiency is a result of surface redox reactions facilitated by electron and hole transfer, resulting in the production of Reactive oxygen species (ROS) such as O2•- and •OH. Additionally, antioxidant experiments were performed to confirm the ROS generation capability of MENCs under magnetic field excitation. Furthermore, trapping experiments performed employing specific scavengers for individual reactive species reveal the mechanism responsible for the magnetic field-driven catalytic breakdown of organic contaminants by MENCs. Interestingly, the MENCs exhibit >95% reduction in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria, respectively, within 90 min of exposure to a (20 mT& 1.9 kHz) AC magnetic field.

Deciphering the enigmatic PilY1 of Acidithiobacillus thiooxidans: An in silico analysis

Thirty years since the first report on the PilY1 protein in bacteria, only the C-terminal domain has been crystallized; there is no study in which the N-terminal domain, let alone the complete protein, has been crystallized. In our laboratory, we are interested in characterizing the Type IV Pili (T4P) of Acidithiobacillus thiooxidans. We performed an in silico characterization of PilY1 and other pilins of the T4P of this acidophilic bacterium. In silico characterization is crucial for understanding how proteins adapt and function under extreme conditions. By analyzing the primary and secondary structures of proteins through computational methods, researchers can gain valuable insights into protein stability, key structural features, and unique amino acid compositions that contribute to resilience in harsh environments. Here, it is presented a description of the particularities of At. thiooxidans PilY1 through predictor software and homology data. Our results suggest that PilY1 from At. thiooxidans may have the same role as has been described for other PilY1 associated with T4P in neutrophilic bacteria; also, its C-terminal interacts (interface interaction) with the minor pilins PilX, PilW and PilV. The N-terminal region comprises domains such as the vWA and the MIDAS, involved in signaling, ligand-binding, and protein-protein interaction. In fact, the vWA domain has intrinsically disordered regions that enable it to maintain its structure over a wide pH range, not only at extreme acidity to which At. thiooxidans is adapted. The results obtained helped us design the correct methodology for its heterologous expression. This allowed us partially experimentally characterize it by obtaining the N-terminal domain recombinantly and evaluating its acid stability through fluorescence spectroscopy. The data suggest that it remains stable across pH changes. This work thus provides guidance for the characterization of extracellular proteins from extremophilic organisms.

Multiple biological characteristics and functions of intestinal biofilm extracellular polymers: friend or foe?

The gut microbiota is vital to human health, and their biofilms significantly impact intestinal immunity and the maintenance of microbial balance. Certain pathogens, however, can employ biofilms to elude identification by the immune system and medical therapy, resulting in intestinal diseases. The biofilm is formed by extracellular polymorphic substances (EPS), which shield microbial pathogens from the host immune system and enhance its antimicrobial resistance. Therefore, investigating the impact of extracellular polysaccharides released by pathogens that form biofilms on virulence and defence mechanisms is crucial. In this review, we provide a comprehensive overview of current pathogenic biofilm research, deal with the role of extracellular polymers in the formation and maintenance of pathogenic biofilm, and elaborate different prevention and treatment strategies to provide an innovative approach to the treatment of intestinal pathogen-based diseases.

Development of Antimicrobial Surfaces Using Diamond-like Carbon or Diamond-like Carbon-Based Coatings

The medical device market is a high-growth sector expected to sustain an annual growth rate of over 5%, even in developed countries. Daily, numerous patients have medical devices implanted or inserted within their bodies. While medical devices have significantly improved patient outcomes, as foreign objects, their wider use can lead to an increase in device-related infections, thereby imposing a burden on healthcare systems. Multiple materials with significant societal impact have evolved over time: the 19th century was the age of iron, the 20th century was dominated by silicon, and the 21st century is often referred to as the era of carbon. In particular, the development of nanocarbon materials and their potential applications in medicine are being explored, although the scope of these applications remains limited. Technological innovations in carbon materials are remarkable, and their application in medicine is expected to advance greatly. For example, diamond-like carbon (DLC) has garnered considerable attention for the development of antimicrobial surfaces. Both DLC itself and its derivatives have been reported to exhibit anti-microbial properties. This review discusses the current state of DLC-based antimicrobial surface development.

Nanocomposite system with photoactive phloxine B eradicates resistant Staphylococcus aureus

Nanomaterials modified with hybrid films functionalized with photoactive compounds can be an effective system to prevent and eradicate biofilms on medical devices. The aim of this research was to extend current knowledge on nanomaterial comprised of polyurethane (PU) modified with a nanocomposite film of organoclay with the functionalized photosensitizer (PS) phloxine B (PhB). Particles of the clay mineral saponite were, at first modified by octadecyltrimethylammonium cations to activate the surface for PhB adsorption. The colloids were filtered to get silicate films on polytetrafluoroethylene membrane filters, which were layered with a liquid mixture of PU precursors. The penetration of PU into the silicate formed a thin nanocomposite film. This nanomaterial demonstrated excellent effectiveness against methicillin-resistant S. aureus (MRSA) resistant to fluoroquinolones (L12 and S61, respectively). It showed more than 1000- and 10 000-fold inhibition of biofilm growth after irradiation with green laser compared to the unmodified PU material. Principal component analysis and multiple linear regression showed that the effectiveness of the nanomaterial was not influenced by virulence factors such as the expression of efflux pumps of the Nor family, the adhesin PIA encoded by the icaADBC operon or the robustness of the biofilms. However, the presence of organoclay, PhB and irradiation had a significant effect on the anti-biofilm properties of the nanocomposite. The anti-microbial properties of the material were strengthened after irradiation, because of high reactive oxygen species release (more than 14-fold compared to non-irradiated sample). Materials based on photoactive molecules can represent a worthwhile pathway towards the development of more complex nanomaterials applicable in various fields of medicine.

Fighting against biofilm: The antifouling and antimicrobial material

Biofilms are groups of microorganisms protected by self-secreted extracellular substances. Biofilm formation on the surface of biomaterial or engineering materials becomes a severe challenge. It has caused significant health, environmental, and societal concerns. It is believed that biofilms lead to life-threatening infection, medical implant failure, foodborne disease, and marine biofouling. To address these issues, tremendous effort has been made to inhibit biofilm formation on materials. Biofilms are extremely difficult to treat once formed, so designing material and coating bearing functional groups that are capable of resisting biofilm formation has attracted increasing attention for the last two decades. Many types of antibiofilm strategies have been designed to target different stages of biofilm formation. Development of the antibiofilm material can be classified into antifouling material, antimicrobial material, fouling release material, and integrated antifouling/antimicrobial material. This review summarizes relevant research utilizing these four approaches and comments on their antibiofilm properties. The feature of each method was compared to reveal the research trend. Antibiofilm strategies in fundamental research and industrial applications were summarized.

Microbial community and extracellular polymeric substance dynamics in arid-zone temporary pan ecosystems

Microbial extracellular polymeric substances (EPS) are an important component in sediment ecology. However, most research is highly skewed towards the northern hemisphere and in more permanent systems. This paper investigates EPS (i.e., carbohydrates and proteins) dynamics in arid Austral zone temporary pans sediments. Colorimetric methods and sequence-based metagenomics techniques were employed in a series of small temporary pan ecosystems characterised by alternating wet and dry hydroperiods. Microbial community patterns of distribution were evaluated between seasons (hot-wet and cool-dry) and across depths (and inferred inundation period) based on estimated elevation. Carbohydrates generally occurred in relatively higher proportions than proteins; the carbohydrate:protein ratio was 2.8:1 and 1.6:1 for the dry and wet season respectively, suggesting that EPS found in these systems was largely diatom produced. The wet- hydroperiods (Carbohydrate mean 102 μg g-1; Protein mean 65 μg g-1) supported more EPS production as compared to the dry- hydroperiods (Carbohydrate mean 73 μg g-1; Protein mean 26 μg g-1). A total of 15,042 Unique Amplicon Sequence Variants (ASVs) were allocated to 51 bacterial phyla and 1127 genera. The most abundant genera had commonality in high temperature tolerance, with Firmicutes, Actinobacteria and Proteobacteria in high abundances. Microbial communities were more distinct between seasons compared to within seasons which further suggested that the observed metagenome functions could be seasonally driven. This study's findings implied that there were high levels of denitrification by mostly nitric oxide reductase and nitrite reductase enzymes. EPS production was high in the hot-wet season as compared to relatively lower rates of nitrification in the cool-dry season by ammonia monooxygenases. Both EPS quantities and metagenome functions were highly associated with availability of water, with high rates being mainly associated with wet- hydroperiods compared to dry- hydroperiods. These data suggest that extended dry periods threaten microbially mediated processes in temporary wetlands, with implications to loss of biodiversity by desiccation.

Enhanced Antibacterial Properties of Titanium Surfaces through Diversified Ion Plating with Silver Atom Deposition

In this study, we investigate the antibacterial effect of silver atoms implanted into a thin surface layer of titanium at low energies using an alternative ion plating technology called Diversified Ion Plating. Silver atoms were incorporated into titanium samples using reactive low-voltage ion plating at 2 keV and 4 keV. Surface modifications and morphology were evaluated using wettability, profilometry measurements, and energy-dispersive spectroscopy. For a precise determination of the quantity and depth of implanted silver atoms on titanium surfaces, a combination of experimental techniques such as Rutherford Backscattering Spectrometry along with Monte Carlo simulations were utilized. To assess the antibacterial effects of the silver atoms incorporated into pure titanium surfaces, bacterial suspension immersion tests were performed with a standard strain of Staphylococcus aureus (ATCC 12600). The outcomes indicate that titanium surfaces implanted with silver atoms were more effective in inhibiting the growth of Staphylococcus aureus than pure titanium surfaces. Better results were found when the deposition was performed at 4 keV, indicating that a deeper implantation of silver, spanning a few nanometers, can result in a longer and more effective release of silver atoms. These findings suggest the potential for the development of new, cost-effective biomaterials, paving the way for improved implant materials in various health-related applications.

Cyclic olefin copolymer (COC) as a promising biomaterial for affecting bacterial colonization: investigation on Vibrio campbellii

Cyclic olefin copolymer (COC) has emerged as an interesting biocompatible material for Organ-on-a-Chip (OoC) devices monitoring growth, viability, and metabolism of cells. Despite ISO 10993 approval, systematic investigation of bacteria grown onto COC is a still not documented issue. This study discusses biofilm formations of the canonical wild type BB120 Vibrio campbellii strain on a native COC substrate and addresses the impact of the physico-chemical properties of COC compared to conventional hydroxyapatite (HA) and poly(dimethylsiloxane) (PDMS) surfaces. An interdisciplinary approach combining bacterial colony counting, light microscopy imaging and advanced digital image processing remarks interesting results. First, COC can reduce biomass adhesion with respect to common biopolymers, that is suitable for tuning biofilm formations in the biological and medical areas. Second, remarkably different biofilm morphology (dendritic complex patterns only in the case of COC) was observed among the examined substrates. Third, the observed biofilm morphogenesis was related to the interaction of COC with the conditioning layer of the planktonic biological medium. Fourth, Level Co-occurrence Matrix (CGLM)-based analysis enabled quantitative assessment of the biomass textural fractal development under different coverage conditions. All of this is of key practical relevance in searching innovative biocompatible materials for pharmaceutical, implantable and medical products.

Deciphering the behavior and potential mechanism of biochar at different pyrolysis temperatures to alleviate membrane biofouling

Biofouling limits applications of membrane technology in wastewater treatment, but dosing additives to membrane tanks is an effective method to alleviate biofouling. In this study, biochar derived from corncob and pyrolyzed at 300, 500, and 700°C was dosed to determine the underlying anti-biofouling mechanism. The effects of the biochar on the membrane properties and foulant behavior were systematically investigated. The results showed that biochar delayed the occurrence of the fouling transition (0.5-3.0 h), and decreased the flux decline rate, thus achieving a higher water flux (3.1-3.7 times of the control group). Biochar altered membrane surface properties, and increased the membrane surface charge, roughness, and hydrophilicity, which all contributed to higher membrane permeability. Moreover, adding biochar reduced the number of foulants in the fouling layer, particularly protein substances. The flux model fit and the XDLVO theory further revealed the mitigating effect of biochar on membrane biofouling. At the initial intermediate-blocking stage, the effect of biochar on membrane fouling was determined by its properties, and adsorption capacity to the foulants, BC500 presented the best mitigation performance. At the later cake-filtration stage, the role of biochar in membrane fouling was strongly associated with protein content in the fouling layer, and the minimum rate of flux decline occurred in BC300. This study promotes the understanding and development of biochar to alleviate membrane biofouling.

Biofilm formation by sulphate-reducing bacteria on different metals and their prospective role in titanium corrosion

This study describes the biofilm formation by sulphate-reducing bacteria (SRB) on different materials, which has implications for the biomedical, pharmaceutical, food and chemical process industries. SRB was chosen as a model organism being an anaerobic bacterium. Biofilm formation on different materials and corrosion of titanium by SRB were monitored with time using confocal laser scanning microscopy and fluorescent FISH probes were used to authenticate the SRB strain. The thickness of the mono-culture SRB biofilm has ranged from 4 to 24 µm during thed 12-84 hr; however, the maximum biofilm thickness (24 µm) was recorded after 60 hr of growth. Planktonic growth of the SRB strain showed a log phase up to 48 hr and the sulphide production ranged from 2 to 14 mg l-1. For a comparative account, the SRB biofilm formation on copper was chosen as a positive control. Finally, the putative role of extracellular electron transfer by SRB in the biocorrosion process and the plausible mechanism of pitting corrosion of titanium is described in detail.

Accumulation and depletion of E. coli in surfaces mediated by curvature

Can topography be used to control bacteria accumulation? We address this question in the model system of smooth-swimming and run-and-tumble Escherichia coli swimming near a sinusoidal surface, and show that the accumulation of bacteria is determined by the characteristic curvature of the surface. For low curvatures, cells swim along the surface due to steric alignment and are ejected from the surface when they reach the peak of the sinusoid. Increasing curvature enhances this effect and reduces the density of bacteria in the curved surface. However, for curvatures larger than κ^{*}≈0.25µm^{-1}, bacteria become trapped in the valleys, where they can remain for long periods of time. Minimal simulations considering only steric interactions with the surface reproduce these results and give insights into the physical mechanisms defining the critical curvature, which is found to scale with the inverse of the bacterial length. We show that for curvatures larger than κ^{*}, the otherwise stable alignment with the wall becomes unstable while the stable orientation is now perpendicular to the wall, thus predicting accurately the onset of trapping at the valleys.

Effect of flux and shear rate on E. coli recovery in tangential flow filtration through a single hollow fiber

Pathogenic bacteria which enter a viable but non-culturable (VBNC) state impede efforts to reach detectable concentrations required for PCR methods. This motivated a strategy for tangential flow filtration to concentrate bacteria in aqueous samples while maintaining the bacteria in a viable state, maximizing their recovery and achieving high fluxes through a single hollow fiber membrane. Filtrations were carried out for green fluorescent protein (GFP) E. coli at high shear rates (up to 27,000 sec-1) through 0.2 μm cut-off polyethersulfone (PES) microfilter membranes or 50 kDa polysulfone (PS) ultrafilter membranes. High shear minimized bacterial attachment on membrane surfaces, which would otherwise occur due to forced convection of the particles to the membrane surface at high flux conditions. Single fiber filter modules were constructed to facilitate concentration of Escherichia coli at fluxes ranging from 55 to 4500 L m-2 h-1. The effect of high shear rates on bacterial viability was found to be minimal with bacterial losses during filtration caused principally by their accumulation on the membrane surface. Recoveries of 90% were achievable at high shear rates when the average flux was ≤300 L m-2 h-1. This corresponded to a 3-h filtration time for a 225 mL sample through a single hollow fiber. Detectable bacteria concentrations of 1800 colony-forming unit (CFU)/mL were achieved for starting concentrations of 140 CFU/mL.

Responsively Degradable Nanoarmor-Assisted Super Resistance and Stable Colonization of Probiotics for Enhanced Inflammation-Targeted Delivery

Manipulation of the gut microbiota using oral microecological preparations has shown great promise in treating various inflammatory disorders. However, delivering these preparations while maintaining their disease-site specificity, stability, and therapeutic efficacy is highly challenging due to the dynamic changes associated with pathological microenvironments in the gastrointestinal tract. Herein, a superior armored probiotic with an inflammation-targeting capacity is developed to enhance the efficacy and timely action of bacterial therapy against inflammatory bowel disease (IBD). The coating strategy exhibits suitability for diverse probiotic strains and has negligible influence on bacterial viability. This study demonstrates that these armored probiotics have ultraresistance to extreme intraluminal conditions and stable mucoadhesive capacity. Notably, the HA-functionalized nanoarmor equips the probiotics with inflamed-site targetability through multiple interactions, thus enhancing their efficacy in IBD therapy. Moreover, timely "awakening" of ingested probiotics through the responsive transferrin-directed degradation of the nanoarmor at the site of inflammation is highly beneficial for bacterial therapy, which requires the bacterial cells to be fully functional. Given its easy preparation and favorable biocompatibility, the developed single-cell coating approach provides an effective strategy for the advanced delivery of probiotics for biomedical applications at the cellular level.

Bacteria-surface interactions: role of impacting bacteria-laden droplets

Understanding the interactions of pathogenic droplets with surfaces is crucial to biomedical applications. In this study, using E. coli as the model microbe, we investigate the impact of a bacteria-laden droplet on different substrates, both bare and antimicrobial. In doing so, we unveil the significance of kinetic energy and spreading parameters of the impacting droplet in determining the microbes' proliferation capabilities. Our results indicate an inverse relationship between the impact Weber number and the bacterial ability to proliferate. We reveal that the mechanical stress generated during impact impedes the capabilities of microbes present inside the droplet to create their progeny. Following an order analysis of the mechanical stress generated, we argue that the impact does not induce lysis-driven cell death of the bacteria; rather, it promotes a stress-driven transition of viable bacteria to a viable-but-non-culturable (VBNC) state. Furthermore, variations in the concentration of particles on the antimicrobial surfaces revealed the role of the post-impact spreading behaviour in dictating bacterial proliferation capabilities. Contrary to the conventional notion, we demonstrate that during the early stages of interaction, a bare substrate may outperform an antibacterial substrate in the inactivation of the bacterial load. Finally, we present an interaction map illustrating the complex relationship between bacterial colony-forming units, bactericide concentration on the surface, and the impact Weber number. We believe that the inferences of the study, highlighting the effect of mechanical stresses on the soft cell wall of microbes, could be a useful design consideration for the development of antimicrobial surfaces.

Interdisciplinary-Inspired Smart Antibacterial Materials and Their Biomedical Applications

The discovery of antibiotics has saved millions of lives, but the emergence of antibiotic-resistant bacteria has become another problem in modern medicine. To avoid or reduce the overuse of antibiotics in antibacterial treatments, stimuli-responsive materials, pathogen-targeting nanoparticles, immunogenic nano-toxoids, and biomimetic materials are being developed to make sterilization better and smarter than conventional therapies. The common goal of smart antibacterial materials (SAMs) is to increase the antibiotic efficacy or function via an antibacterial mechanism different from that of antibiotics in order to increase the antibacterial and biological properties while reducing the risk of drug resistance. The research and development of SAMs are increasingly interdisciplinary because new designs require the knowledge of different fields and input/collaboration from scientists in different fields. A good understanding of energy conversion in materials, physiological characteristics in cells and bacteria, and bactericidal structures and components in nature are expected to promote the development of SAMs. In this review, the importance of multidisciplinary insights for SAMs is emphasized, and the latest advances in SAMs are categorized and discussed according to the pertinent disciplines including materials science, physiology, and biomimicry.

Metabolic insights from mass spectrometry imaging of biofilms: A perspective from model microorganisms

Biofilms are dense aggregates of bacterial colonies embedded inside a self-produced polymeric matrix. Biofilms have received increasing attention in medical, industrial, and environmental settings due to their enhanced survival. Their characterization using microscopy techniques has revealed the presence of structural and cellular heterogeneity in many bacterial systems. However, these techniques provide limited chemical detail and lack information about the molecules important for bacterial communication and virulence. Mass spectrometry imaging (MSI) bridges the gap by generating spatial chemical information with unmatched chemical detail, making it an irreplaceable analytical platform in the multi-modal imaging of biofilms. In the last two decades, over 30 species of biofilm-forming bacteria have been studied using MSI in different environments. The literature conveys both analytical advancements and an improved understanding of the effects of environmental variables such as host surface characteristics, antibiotics, and other species of microorganisms on biofilms. This review summarizes the insights from frequently studied model microorganisms. We share a detailed list of organism-wide metabolites, commonly observed mass spectral adducts, culture conditions, strains of bacteria, substrate, broad problem definition, and details of the MS instrumentation, such as ionization sources and matrix, to facilitate future studies. We also compared the spatial characteristics of the secretome under different study designs to highlight changes because of various environmental influences. In addition, we highlight the current limitations of MSI in relation to biofilm characterization to enable cross-comparison between experiments. Overall, MSI has emerged to become an important approach for the spatial/chemical characterization of bacterial biofilms and its use will continue to grow as MSI becomes more accessible.

Iron coatings on carbonate rocks shape the attached bacterial aquifer community

Most studies of groundwater ecosystems target planktonic microbes, which are easily obtained via water samples. In contrast, little is known about the diversity and function of microbes adhering to rock surfaces, particularly to consolidated rocks. To investigate microbial attachment to rock surfaces, we incubated rock chips from fractured aquifers in limestone-mudstone alternations in bioreactors fed with groundwater from two wells representing oxic and anoxic conditions. Half of the chips were coated with iron oxides, representing common secondary mineralization in fractured rock. Our time-series analysis showed bacteria colonizing the chips within two days, reaching cell numbers up to 4.16 × 105 cells/mm2 after 44 days. Scanning electron microscopy analyses revealed extensive colonization but no multi-layered biofilms, with chips from oxic bioreactors more densely colonized than from anoxic ones. Estimated attached-to-planktonic cell ratios yielded values of up to 106: 1 and 103: 1, for oxic and anoxic aquifers, respectively. We identified distinct attached and planktonic communities with an overlap between 17 % and 42 %. Oxic bioreactors were dominated by proteobacterial genera Aquabacterium and Rhodoferax, while Rheinheimera and Simplicispira were the key players of anoxic bioreactors. Motility, attachment, and biofilm formation traits were predicted in major genera based on groundwater metagenome-assembled genomes and reference genomes. Early rock colonizers appeared to be facultative autotrophs, capable of fixing CO2 to synthesize biomass and a biofilm matrix. Late colonizers were predicted to possess biofilm degrading enzymes such as beta-glucosidase, beta-galactosidase, amylases. Fe-coated chips of both bioreactors featured more potential iron reducers and oxidizers than bare rock chips. As secondary minerals can also serve as energy source, they might favor primary production and thus contribute to subsurface ecosystem services like carbon fixation. Since most subsurface microbes seem to be attached, their contribution to ecosystem services should be considered in future studies.

Increasing transposase abundance with ocean depth correlates with a particle-associated lifestyle

Transposases are mobile genetic elements that move within and between genomes, promoting genomic plasticity in microorganisms. In marine microbial communities, the abundance of transposases increases with depth, but the reasons behind this trend remain unclear. Our analysis of metagenomes from the Tara Oceans and Malaspina Expeditions suggests that a particle-associated lifestyle is the main covariate for the high occurrence of transposases in the deep ocean, and this trend holds true for individual genomes as well as in a community-wide sense. We observed a strong and depth-independent correlation between transposase abundance and the presence of biofilm-associated genes, as well as the prevalence of secretory enzymes. This suggests that mobile genetic elements readily propagate among microbial communities within crowded biofilms. Furthermore, we show that particle association positively correlates with larger genome size, which is in turn associated with higher transposase abundance. Cassette sequences associated with transposons are enriched with genes related to defense mechanisms, which are more highly expressed in the deep sea. Thus, while transposons spread at the expense of their microbial hosts, they also introduce novel genes and potentially benefit the hosts in helping to compete for limited resources. Overall, our results suggest a new understanding of deep ocean particles as highways for gene sharing among defensively oriented microbial genomes.IMPORTANCEGenes can move within and between microbial genomes via mobile genetic elements, which include transposases and transposons. In the oceans, there is a puzzling increase in transposase abundance in microbial genomes as depth increases. To gain insight into this trend, we conducted an extensive analysis of marine microbial metagenomes and metatranscriptomes. We found a significant correlation between transposase abundance and a particle-associated lifestyle among marine microbes at both the metagenome and genome-resolved levels. We also observed a link between transposase abundance and genes related to defense mechanisms. These results suggest that as microbes become densely packed into crowded particles, mobile genes are more likely to spread and carry genetic material that provides a competitive advantage in crowded habitats. This may enable deep sea microbes to effectively compete in such environments.

Antibiotic Resistant Biofilms and the Quest for Novel Therapeutic Strategies

Antimicrobial resistance (AMR) is one of the major leading causes of death around the globe. Present treatment pipelines are insufficient to overcome the critical situation. Prominent biofilm forming human pathogens which can thrive in infection sites using adaptive features results in biofilm persistence. Considering the present scenario, prudential investigations into the mechanisms of resistance target them to improve antibiotic efficacy is required. Regarding this, developing newer and effective treatment options using edge cutting technologies in medical research is the need of time. The reasons underlying the adaptive features in biofilm persistence have been centred on different metabolic and physiological aspects. The high tolerance levels against antibiotics direct researchers to search for novel bioactive molecules that can help combat the problem. In view of this, the present review outlines the focuses on an opportunity of different strategies which are in testing pipeline can thus be developed into products ready to use.

A versatile micromodel technology to explore biofilm development in porous media flows

Bacterial biofilms that grow in porous media are critical to ecosystem processes and applications ranging from soil bioremediation to bioreactors for treating wastewater or producing value-added products. However, understanding and engineering the complex phenomena that drive the development of biofilms in such systems remains a challenge. Here we present a novel micromodel technology to explore bacterial biofilm development in porous media flows. The technology consists of a set of modules that can be combined as required for any given experiment and conveniently tuned for specific requirements. The core module is a 3D-printed micromodel where biofilm is grown into a perfusable porous substrate. High-precision additive manufacturing, in particular stereolithography, is used to fabricate porous scaffolds with precisely controlled architectures integrating flow channels with diameters down to several hundreds of micrometers. The system is instrumented with: ultraviolet-C light-emitting diodes; on-line measurements of oxygen consumption and pressure drop across the porous medium; camera and spectrophotometric cells for the detection of biofilm detachment events at the outlet. We demonstrate how this technology can be used to study the development of Pseudomonas aeruginosa biofilm for several days within a network of flow channels. We find complex dynamics whereby oxygen consumption reaches a steady-state but not the pressure drop, which instead features a permanent regime with large fluctuations. We further use X-ray computed microtomography to image the spatial distribution of biofilms and computational fluid dynamics to link biofilm development with local flow properties. By combining the advantages of additive manufacturing for the creation of reproducible 3D porous microarchitectures with the flow control and instrumentation accuracy of microfluidics, our system provides a platform to study the dynamics of biofilm development in 3D porous media and to rapidly test new concepts in process engineering.

Mechanical constraints to unbound expansion of B. subtilis on semi-solid surfaces

IMPORTANCE

How bacterial cells colonize new territory is a problem of fundamental microbiological and biophysical interest and is key to the emergence of several phenomena of biological, ecological, and medical relevance. Here, we demonstrate how bacteria stuck in a colony of finite size can resume exploration of new territory by aquaplaning and how they fine tune biofilm viscoelasticity to surface material properties that allows them differential mobility. We show how changing local interfacial forces and colony viscosity results in a plethora of bacterial morphologies on surfaces with different physical and mechanical properties.

Environmental and ecological importance of bacterial extracellular vesicles (BEVs)

Extracellular vesicles are unique structures released by the cells of all life forms. Bacterial extracellular vesicles (BEVs) were found in various ecosystems and natural habitats. They are associated with bacterial-bacterial interactions as well as host-bacterial interactions in the environment. Moreover, BEVs facilitate bacterial adaptation to a variety of environmental conditions. BEVs were found to be abundant in the environment, and therefore they can regulate a broad range of environmental processes. In the environment, BEVs can serve as tools for cell-to-cell interaction, secreting mechanism of unwanted materials, transportation, genetic materials exchange and storage, defense and protection, growth support, electron transfer, and cell-surface interplay regulation. Thus, BEVs have a great potential to be used in a variety of environmental applications such as serving as bioremediating reagents for environmental disaster mitigation as well as removing problematic biofilms and waste treatment. This research area needs to be investigated further to disclose the full environmental and ecological importance of BEVs as well as to investigate how to harness BEVs as effective tools in a variety of environmental applications.

Perfluoropolyether-incorporated polyurethane with enhanced antibacterial and anti-adhesive activities for combating catheter-induced infection

To avoid the undesired bacterial attachment on polyurethane-based biomedical devices, we designed a class of novel perfluoropolyether-incorporated polyurethanes (PFPU) containing different contents of perfluoropolyether (PFPE) segments. After blending with Ag nanoparticles (AgNPs), a series of bifunctional PFPU/AgNPs composites with bactericidal and anti-adhesion abilities were obtained and correspondingly made into PFPU/AgNPs films (PFPU/Ag-F) using a simple solvent-casting method. Due to its highest hydrophobicity and suitable mechanical properties, PFPU8/Ag-F containing 8 mol% of PFPE content was chosen as the optimized one for the next antibacterial assessment. The PFPU8/Ag-F can effectively deactivate over 99.9% of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) cells at 106 CFU mL-1 within 30 min. Furthermore, the PFPU8/AgNPs composite was used as painting material to form a protective coating for the commercial polyurethane (PU) catheter. The as-prepared PFPU8/Ag coating exhibits high resistance to bacterial adhesion in a continuous-flow artificial urine model in an 8 day exposure. Therefore, it can be expected that the proposed PFPE-containing films and coatings can effectively prevent bacterial colonization and biofilm formation on catheters or other implants, thereby reducing the risk of postoperative catheter-induced infection.

Short-term plastisphere colonization dynamics across six plastic types

Marine plastic pollution is a major concern worldwide, but the understanding of plastisphere dynamics remains limited in the southern hemisphere. To address this knowledge gap, we conducted a study in South Australia to investigate the prokaryotic community of the plastisphere and its temporal changes over 4 weeks. We submerged six plastic types (i.e., High-Density Polyethylene [HDPE], Polyvinyl chloride [PVC], Low-Density Polyethylene [LDPE], Polypropylene [PP], Polystyrene [PS] and the understudied textile, polyester [PET]) and wood in seawater and sampled them weekly to characterize the prokaryotic community using 16S rRNA gene metabarcoding. Our results showed that the plastisphere composition shifted significantly over short time scales (i.e., 4 weeks), and each plastic type had distinct groups of unique genera. In particular, the PVC plastisphere was dominated by Cellvibrionaceae taxa, distinguishing it from other plastics. Additionally, the textile polyester, which is rarely studied in plastisphere research, supported the growth of a unique group of 25 prokaryotic genera (which included the potential pathogenic Legionella genus). Overall, this study provides valuable insights into the colonization dynamics of the plastisphere over short time scales and contributes to narrowing the research gap on the southern hemisphere plastisphere.

Plasmonic inhibition of bacterial adhesion on gold-decorated mesoporous zirconium oxide thin films

Preventing bacterial development on surfaces is essential to avoid problems caused by biofouling. Surfaces decorated with gold nanoparticles have been shown to thermally kill bacteria under high-intensity NIR illumination. In this study, we evaluated the colonization by E. coli of nanostructured surfaces composed of mesoporous zirconia thin films, both with and without gold nanoparticles embedded into the pores. We studied the effect of the nanostructure and of low intensity visible light excitation of the gold nanoparticles on the colonization process. We found that neither the zirconia, nor the presence of pores, or even gold nanoparticles affect bacterial adhesion compared to the bare glass substrate. Therefore, mesoporous zirconia thin films are biologically inert scaffolds that enable the construction of robust surfaces containing functional nanoparticles that can affect bacterial growth. When the gold containing surfaces are irradiated with light, bacterial adhesion shows a remarkable 96 ± 4% reduction. Our studies revealed that these surfaces affect early colonization steps, prior to biofilm formation, preventing bacterial adhesion without affecting its viability. In contrast to related systems where plasmonic excitation induces membrane damage due to strong local heating, the membrane integrity is preserved, showing that these surfaces have a different working principle.

Thin-film nanocomposite membranes for efficient removal of emerging pharmaceutical organic contaminants from water

Membranes are receiving significant attention to remove emerging organic micropollutants (OMPs) from wastewater and natural water sources. Herein, we report the facile preparation of a novel thin-film nanocomposite (TFN) membrane with high permeability and efficient removal of OMPs. ZnO nanoparticles were first synthesized using the co-precipitation method and functionalized with N1-(3-Trimethoxysilylpropyl)diethylenetriamine to make the surface rich with amine groups and then synthesized nanomaterials were covalently cross-linked into the active layer during the interfacial polymerization (IP) process. The performance of the membranes containing the cross-linked ZnO was significantly better than the non-cross-linked ZnO NPs containing membranes. Adding multiple hydrophilic groups and entities on the surface significantly decreased the contact angle (from ∼60° to 20°). SEM images confirmed the uniform presence and homogeneous distribution of the functionalized NPs throughout the entire membrane surface. Zeta potential measurements showed the modified membranes have a lower negative charge than the pristine membranes. Filtration studies revealed a significant increase in permeability ascribed to the creation of nanochannels in the membrane's active layer. The modified membranes outperformed commercial NF membranes in removing four common OMPs with rejection efficiencies of ∼30%, 64%, 60%, and 70% for Sulfamethoxazole, Amitriptyline, Omeprazole, and Loperamide HCl, respectively. The higher removal efficiency was attributed to the weakened hydrophobic interactions due to the presence of hydrophilic moieties and a stronger size exclusion effect. Moreover, the modified membranes showed high resistance to bacterial adhesion in static conditions.

Flagellar motor remodeling during swarming requires FliL

FliL is an essential component of the flagellar machinery in some bacteria, but a conditional one in others. The conditional role is for optimal swarming in some bacteria. During swarming, physical forces associated with movement on a surface are expected to exert a higher load on the flagellum, requiring more motor torque to move. FliL was reported to enhance motor output in several bacteria and observed to assemble as a ring around ion-conducting stators that power the motor. In this study we identify a common new function for FliL in diverse bacteria-Escherichia coli, Bacillus subtilis, and Proteus mirabilis. During swarming, all these bacteria show increased cell speed and a skewed motor bias that suppresses cell tumbling. We demonstrate that these altered motor parameters, or "motor remodeling," require FliL. Both swarming and motor remodeling can be restored in an E. coli fliL mutant by complementation with fliL genes from P. mirabilis and B. subtilis, showing conservation of a swarming-associated FliL function across phyla. In addition, we demonstrate that the strong interaction we reported earlier between FliL and the flagellar MS-ring protein FliF is confined to the RBM-3 domain of FliF that links the periplasmic rod to the cytoplasmic C-ring. This interaction may explain several phenotypes associated with the absence of FliL.

Phosphate starvation decouples cell differentiation from DNA replication control in the dimorphic bacterium Caulobacter crescentus

Upon nutrient depletion, bacteria stop proliferating and undergo physiological and morphological changes to ensure their survival. Yet, how these processes are coordinated in response to distinct starvation conditions is poorly understood. Here we compare the cellular responses of Caulobacter crescentus to carbon (C), nitrogen (N) and phosphorus (P) starvation conditions. We find that DNA replication initiation and abundance of the replication initiator DnaA are, under all three starvation conditions, regulated by a common mechanism involving the inhibition of DnaA translation. By contrast, cell differentiation from a motile swarmer cell to a sessile stalked cell is regulated differently under the three starvation conditions. During C and N starvation, production of the signaling molecules (p)ppGpp is required to arrest cell development in the motile swarmer stage. By contrast, our data suggest that low (p)ppGpp levels under P starvation allow P-starved swarmer cells to differentiate into sessile stalked cells. Further, we show that limited DnaA availability, and consequently absence of DNA replication initiation, is the main reason that prevents P-starved stalked cells from completing the cell cycle. Together, our findings demonstrate that C. crescentus decouples cell differentiation from DNA replication initiation under certain starvation conditions, two otherwise intimately coupled processes. We hypothesize that arresting the developmental program either as motile swarmer cells or as sessile stalked cells improves the chances of survival of C. crescentus during the different starvation conditions.

Accurate Prediction of Antimicrobial Susceptibility for Point-of-Care Testing of Urine in Less than 90 Minutes via iPRISM Cassettes

The extensive and improper use of antibiotics has led to a dramatic increase in the frequency of antibiotic resistance among human pathogens, complicating infectious disease treatments. In this work, a method for rapid antimicrobial susceptibility testing (AST) is presented using microstructured silicon diffraction gratings integrated into prototype devices, which enhance bacteria-surface interactions and promote bacterial colonization. The silicon microstructures act also as optical sensors for monitoring bacterial growth upon exposure to antibiotics in a real-time and label-free manner via intensity-based phase-shift reflectometric interference spectroscopic measurements (iPRISM). Rapid AST using clinical isolates of Escherichia coli (E. coli) from urine is established and the assay is applied directly on unprocessed urine samples from urinary tract infection patients. When coupled with a machine learning algorithm trained on clinical samples, the iPRISM AST is able to predict the resistance or susceptibility of a new clinical sample with an Area Under the Receiver Operating Characteristic curve (AUC) of ∼ 0.85 in 1 h, and AUC > 0.9 in 90 min, when compared to state-of-the-art automated AST methods used in the clinic while being an order of magnitude faster.

An Ex-Vivo Model for Investigating Bacterial Extrusion from Infected Root Canals during Masticatory Function

INTRODUCTION

The extrusion of bacteria from infected root canals may lead to increase in symptoms, expansion of periapical lesions, and contribution to systemic diseases. The aim of this study is to investigate a potential proof-of-concept model to study the extent to which bacteria can escape from infected root canals under dynamic loading (simulated chewing).

METHODS

The study was completed in 2 experiments performed at 2 institutions. Biofilms of Streptococcus intermedius in the first experiment and S. intermedius and Actinomyces naeslundii were allowed to grow in root canals of single-rooted extracted teeth for 3 weeks. The roots of the teeth were suspended in a small chamber containing dental transport medium and were mounted on a lower sample holder of a chewing simulator. In the experimental group, simulated chewing cycles equivalent to 1 year of function were conducted, and then bacterial migration was quantified and compared with stationary teeth.

RESULTS

All experimental samples of the loading group revealed bacterial penetration in both experiments. Several of the unloaded samples revealed no bacterial penetration. In the first experiment, a significantly higher number of bacteria were able to escape into the periapex of the loaded group compared with the unloaded group (P = .017). In the second experiment, there was no significant difference between the 2 bacterial species used in the amount of extruded bacteria; however, there was a highly significant effect for occlusal loading (P = .0001).

CONCLUSIONS

The potential for occlusal forces to enhance bacterial extrusion from infected root canals should be further explored.

Progress in Nanostructured Mechano-Bactericidal Polymeric Surfaces for Biomedical Applications

Bacterial infections and antibiotic resistance remain significant contributors to morbidity and mortality worldwide. Despite recent advances in biomedical research, a substantial number of medical devices and implants continue to be plagued by bacterial colonisation, resulting in severe consequences, including fatalities. The development of nanostructured surfaces with mechano-bactericidal properties has emerged as a promising solution to this problem. These surfaces employ a mechanical rupturing mechanism to lyse bacterial cells, effectively halting subsequent biofilm formation on various materials and, ultimately, thwarting bacterial infections. This review delves into the prevailing research progress within the realm of nanostructured mechano-bactericidal polymeric surfaces. It also investigates the diverse fabrication methods for developing nanostructured polymeric surfaces with mechano-bactericidal properties. We then discuss the significant challenges associated with each approach and identify research gaps that warrant exploration in future studies, emphasizing the potential for polymeric implants to leverage their distinct physical, chemical, and mechanical properties over traditional materials like metals.

A Rapidly Responsive Sensor for Wireless Detection of Early and Mature Microbial Biofilms

Biofilm-associated infections, which are able to resist antibiotics, pose a significant challenge in clinical treatments. Such infections have been linked to various medical conditions, including chronic wounds and implant-associated infections, making them a major public-health concern. Early-detection of biofilm formation offers significant advantages in mitigating adverse effects caused by biofilms. In this work, we aim to explore the feasibility of employing a novel wireless sensor for tracking both early-stage and matured-biofilms formed by the medically relevant bacteria Staphylococcus aureus and Pseudomonas aeruginosa. The sensor utilizes electrochemical reduction of an AgCl layer bridging two silver legs made by inkjet-printing, forming a part of near-field-communication tag antenna. The antenna is interfaced with a carbon cloth designed to promote the growth of microorganisms, thereby serving as an electron source for reduction of the resistive AgCl into a highly-conductive Ag bridge. The AgCl-Ag transformation significantly alters the impedance of the antenna, facilitating wireless identification of an endpoint caused by microbial growth. To the best of our knowledge, this study for the first time presents the evidence showcasing that electrons released through the actions of bacteria can be harnessed to convert AgCl to Ag, thus enabling the wireless, battery-less, and chip-less early-detection of biofilm formation.

Incorporating charged Ag@MOFs to boost the antibacterial and filtration properties of porous electrospinning polylactide films

Faced with the pollution caused by particulate matter (PM) in the air, the prevalence of infectious diseases, and the environmental burden by use of nondegradable polymers, the existing filter materials such as meltblown cloth of polypropylene cannot satisfactorily meet people's requirements. In this study, Ag nanoparticles were loaded onto ZIF-8 particles by impregnation reduction to prepare the positively charged Ag@ZIF-8. The porous fibrous membranes of Ag@ZIF-8 with polylactide (PLA) were manufactured by electrostatic spinning technology. Due to the inherently charged feature of Ag@ZIF-8 particles and the presence of pores on fibers, the prepared membranes showed a stable good filtration efficiency of over 97 % at different humidity (30-90%RH, relative humidity). Meanwhile, the presence of charge on Ag@ZIF-8 and the synergistic effects of Ag and ZIF-8 particles made the membranes exhibit good antibacterial effects. The width of the inhibition zone of 3 wt%Ag@ZIF-8/PLA membrane reached 1.33 mm for E. coli and 1.35 mm for S. aureus, respectively.

Biomimetic catheter surface with dual action NO-releasing and generating properties for enhanced antimicrobial efficacy

Infection of indwelling catheters is a common healthcare problem, resulting in higher morbidity and mortality. The vulnerable population reliant on catheters post-surgery for food and fluid intake, blood transfusion, or urinary incontinence or retention is susceptible to hospital-acquired infection originating from the very catheter. Bacterial adhesion on catheters can take place during the insertion or over time when catheters are used for an extended period. Nitric oxide-releasing materials have shown promise in exhibiting antibacterial properties without the risk of antibacterial resistance which can be an issue with conventional antibiotics. In this study, 1, 5, and 10 wt % selenium (Se) and 10 wt % S-nitrosoglutathione (GSNO)-incorporated catheters were prepared through a layer-by-layer dip-coating method to demonstrate NO-releasing and NO-generating capability of the catheters. The presence of Se on the catheter interface resulted in a 5 times higher NO flux in 10% Se-GSNO catheter through catalytic NO generation. A physiological level of NO release was observed from 10% Se-GSNO catheters for 5 d, along with an enhanced NO generation via the catalytic activity as Se was able to increase NO availability. The catheters were also found to be compatible and stable when subjected to sterilization and storage, even at room temperature. Additionally, the catheters showed a 97.02% and 93.24% reduction in the adhesion of clinically relevant strains of Escherichia coli and Staphylococcus aureus, respectively. Cytocompatibility testing of the catheter with 3T3 mouse fibroblast cells supports the material's biocompatibility. These findings from the study establish the proposed catheter as a prospective antibacterial material that can be translated into a clinical setting to combat catheter-related infections.

Rising to the surface: capturing and detecting bacteria by rationally-designed surfaces

Analytical microbiology has made substantial progress since its conception, starting from potato slices, through selective agar media, to engineered surfaces modified with capture probes. While the latter represents the dominant approach in designing sensors for bacteria detection, the importance of sensor surface properties is frequently ignored. Herein, we highlight their significant role in the complex process of bacterial transition from planktonic to sessile, representing the first and critical step in bacteria detection. We present the main surface features and discuss their effect on the bio-solid interface and the resulting sensing capabilities for both flat and particulate systems. The concepts of rationally-designed surfaces for enhanced bacterial detection are presented with recent examples of sensors (capture probe-free) relying solely on surface cues.

The effect of intraoperative immersion solutions on acellular dermal matrix: Biofilm formation and mechanical property

BACKGROUND

Acellular dermal matrix (ADM) is generally used on implant-based breast operations; However, it can increase surgical site infection. Many immersion solutions are applied to ADM, however, the most effective solution is unknown. The purpose of this study is to determine the effect of different solutions on the biofilm formation and mechanical properties of ADM.

METHODS

Aseptic porcine-derived ADMs were immersed in 5 different solutions for 30 min; sterile normal saline, 10% povidone-iodine, 0.5% chlorhexidine, antibiotics (cefazolin, gentamicin, and vancomycin), and taurolidine. They are transferred to 10 ml suspension of methicillin-sensitive/resistant Staphylococcus aureus (MSSA/MRSA) or Staphylococcus epidermidis and an overnight culture was performed. After rinsing and sonication to obtain the biofilm on ADM, colony forming unit (CFU) was measured. In addition, the maximum load before ADM deformation and the elongation length of ADM at the start of the maximum load was determined.

RESULTS

Regardless of strains, povidone-iodine, chlorhexidine, and taurolidine group had lower CFUs than the saline group with statistical significance. Meanwhile, the antibiotics group did not show statistical difference from the saline group. Moreover, only taurolidine group showed higher tensile strength (MRSA, p = 0.0003; S. epidermidis, p = 0.0023) and elongation length (MSSA, p = 0.0015) than the saline group. The antibiotics and chlorhexidine group yielded lower tensile strength and elongation length than the povidone-iodine and taurolidine groups.

CONCLUSIONS

It was suggested that the 10% povidone-iodine or taurolidine solution is effective. In contrast, the antibiotics solution could be considered as an effective intraoperative solution.

Strategies to Mitigate Biofouling of Nanocomposite Polymer-Based Membranes in Contact with Blood

An extracorporeal blood purification method called continuous renal replacement therapy uses a porous hollow-fiber polymeric membrane that is exposed to prolonged contact with blood. In that condition, like with any other submerged filtration membrane, the hemofilter loses its properties over time and use resulting in a rapid decline in flux. The most significant reason for this loss is the formation of a biofilm. Protein, blood cells and bacterial cells attach to the membrane surface in complex and fluctuating processes. Anticoagulation allows for longer patency of vascular access and a longer lifespan of the membrane. Other preventive measures include the modification of the membrane itself. In this article, we focused on the role of nanoadditives in the mitigation of biofouling. Nanoparticles such as graphene, carbon nanotubes, and silica effectively change surface properties towards more hydrophilic, affect pore size and distribution, decrease protein adsorption and damage bacteria cells. As a result, membranes modified with nanoparticles show better flow parameters, longer lifespan and increased hemocompatibility.

Bacterial Drug Delivery Systems for Cancer Therapy: "Why" and "How"

Cancer is one of the major diseases that endanger human health. However, the use of anticancer drugs is accompanied by a series of side effects. Suitable drug delivery systems can reduce the toxic side effects of drugs and enhance the bioavailability of drugs, among which targeted drug delivery systems are the main development direction of anticancer drug delivery systems. Bacteria is a novel drug delivery system that has shown great potential in cancer therapy because of its tumor-targeting, oncolytic, and immunomodulatory properties. In this review, we systematically describe the reasons why bacteria are suitable carriers of anticancer drugs and the mechanisms by which these advantages arise. Secondly, we outline strategies on how to load drugs onto bacterial carriers. These drug-loading strategies include surface modification and internal modification of bacteria. We focus on the drug-loading strategy because appropriate strategies play a key role in ensuring the stability of the delivery system and improving drug efficacy. Lastly, we also describe the current state of bacterial clinical trials and discuss current challenges. This review summarizes the advantages and various drug-loading strategies of bacteria for cancer therapy and will contribute to the development of bacterial drug delivery systems.

Archaeal type IV pili stabilize Haloferax volcanii biofilms in flow

Multicellular communities of contiguous cells attached to solid surfaces called biofilms represent a common microbial strategy to improve resilience in adverse environments.1,2,3 While bacterial biofilms have been under intense investigation, whether archaeal biofilms follow similar assembly rules remains unknown.4,5Haloferax volcanii is an extremely halophilic euryarchaeon that commonly colonizes salt crust surfaces. H. volcanii produces long and thin appendages called type IV pili (T4Ps). These play a role in surface attachment and biofilm formation in both archaea and bacteria. In this study, we employed biophysical experiments to identify the function of T4Ps in H. volcanii biofilm morphogenesis. H. volcanii expresses not one but six types of major pilin subunits that are predicted to compose T4Ps. Non-invasive imaging of T4Ps in live cells using interferometric scattering (iSCAT) microscopy reveals that piliation varies across mutants expressing single major pilin isoforms. T4Ps are necessary to secure attachment of single cells to surfaces, and the adhesive strength of pilin mutants correlates with their level of piliation. In flow, H. volcanii forms clonal biofilms that extend in three dimensions. Notably, the expression of PilA2, a single pilin isoform, is sufficient to maintain levels of piliation, surface attachment, and biofilm formation that are indistinguishable from the wild type. Furthermore, we discovered that fluid flow stabilizes biofilm integrity; as in the absence of flow, biofilms tend to lose cohesion and disperse in a density-dependent manner. Overall, our results demonstrate that T4P-surface and possibly T4P-T4P interactions promote biofilm formation and integrity and that flow is a key factor regulating archaeal biofilm formation.

Lichenysin-like Polypeptide Production by Bacillus licheniformis B3-15 and Its Antiadhesive and Antibiofilm Properties

We report the ability of the crude biosurfactant (BS B3-15), produced by the marine, thermotolerant Bacillus licheniformis B3-15, to hinder the adhesion and biofilm formation of Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 to polystyrene and human cells. First, we attempted to increase the BS yield, optimizing the culture conditions, and evaluated the surface-active properties of cell-free supernatants. Under phosphate deprivation (0.06 mM) and 5% saccharose, the yield of BS (1.5 g/L) increased by 37%, which could be explained by the earlier (12 h) increase in lchAA expression compared to the non-optimized condition (48 h). Without exerting any anti-bacterial activity, BS (300 µg/mL) prevented the adhesion of P. aeruginosa and S. aureus to polystyrene (47% and 36%, respectively) and disrupted the preformed biofilms, being more efficient against S. aureus (47%) than P. aeruginosa (26%). When added to human cells, the BS reduced the adhesion of P. aeruginosa and S. aureus (10× and 100,000× CFU/mL, respectively) without altering the epithelial cells' viability. As it is not cytotoxic, BS B3-15 could be useful to prevent or remove bacterial biofilms in several medical and non-medical applications.