Physico-chemistry of bacterial transmission versus adhesion

Immobilized microalgae: principles, processes and its applications in wastewater treatment

Microalgae have emerged as potential candidates for biomass production and pollutant removal. However, expensive biomass harvesting, insufficient biomass productivity, and low energy intensity limit the large-scale production of microalgae. To break through these bottlenecks, a novel technology of immobilized microalgae culture coupled with wastewater treatment has received increasing attention in recent years. In this review, the characteristics of two immobilized microalgae culture technologies are first presented and then their mechanisms are discussed in terms of biofilm formation theories, including thermodynamic theory, Derjaguin-Landau-Verwei-Overbeek theory (DLVO) and its extended theory (xDLVO), as well as ionic cross-linking mechanisms in the process of microalgae encapsulated in alginate. The main factors (algal strains, carriers, and culture conditions) affecting the growth of microalgae are also discussed. It is also summarized that immobilized microalgae show considerable potential for nitrogen and phosphorus removal, heavy metal removal, pesticide and antibiotic removal in wastewater treatment. The role of bacteria in the cultivation of microalgae by immobilization techniques and their application in wastewater treatment are clarified. This is economically feasible and technically superior. The problems and challenges faced by immobilized microalgae are finally presented.

Risk factor-based clustering of Listeria monocytogenes in food processing environments using principal component analysis

Listeria monocytogenes has a range of strategies that allow it to persist as biofilms in food processing environments (FPE), making it a pathogen of concern to the food industry. The properties of these biofilms are highly variable among strains, and this significantly affects the risk of food contamination. The present study therefore aims to conduct a proof-of-concept study to cluster strains of L. monocytogenes by risk potential using principal component analysis, a multivariate approach. A set of 22 strains, isolated from food processing environments, were typed by serogrouping and pulsed-field gel electrophoresis, showing a relatively high diversity. They were characterized in terms of several biofilm properties that might pose a potential risk of food contamination. The properties studied were tolerance to benzalkonium chloride (BAC), the structural parameters of biofilms (biomass, surface area, maximum and average thickness, surface to biovolume ratio and roughness coefficient) measured by confocal laser scanning microscopy and (3) transfer of biofilm cells to smoked salmon. The PCA correlation circle revealed that the tolerance of biofilms to BAC was positively correlated with roughness, but negatively with biomass parameters. On the contrary, cell transfers were not related to three-dimensional structural parameters, which suggests the role of other variables yet unexplored. Additionally, hierarchical clustering grouped strains into three different clusters. One of them included the strains with high tolerance to BAC and roughness. Another one consisted of strains with enhanced transfer ability, whereas the third cluster contained those that stood out for the thickness of biofilms. The present study represents a novel and effective way to classify L. monocytogenes strains according to biofilm properties that condition the potential risk of reaching the consumer through food contamination. It would thus allow the selection of strains representative of different worst-case scenarios for future studies in support of QMRA and decision-making analysis.

Progress in research on the safety of silicone rubber products in food processing

Silicone rubber (SR) is widely used in the food processing industry due to its excellent physical and chemical properties. However, due to the differences in SR product production formulas and processes, the quality of commercially available SR products varies greatly, with chemical and biological hazard potentials. Residual chemicals in SR, such as siloxane oligomers and 2,4-dichlorobenzoic acid, are non-intentionally added substances, which may migrate into food during processing so the safe use of SR must be guaranteed. Simultaneously, SR in contact with food is susceptible to pathogenic bacteria growing and biofilm formation, like Cronobacter sakazakii, Staphylococcus aureus, Salmonella enteritidis, and Listeria monocytogenes, posing a food safety risk. Under severe usage scenarios such as high-temperature, high-pressure, microwave, and freezing environments with long-term use, SR products are more prone to aging, and their degradation products may pose potential food safety hazards. Based on the goal of ensuring food quality and safety to the greatest extent possible, this review suggests that enterprises need to prepare high-quality food-contact SR products by optimizing the manufacturing formula and production process, and developing products with antibacterial and antiaging properties. The government departments should establish quality standards for food-contact SR products and conduct effective supervision. Besides, the reusable SR products should be cleaned by consumers immediately after use, and the deteriorated products should be replaced as soon as possible.

Antibiofilm Activity and Mechanism of Linalool against Food Spoilage Bacillus amyloliquefaciens

Pellicle biofilm-forming bacteria Bacillus amyloliquefaciens are the major spoilage microorganisms of soy products. Due to their inherent resistance to antibiotics and disinfectants, pellicle biofilms formed are difficult to eliminate and represent a threat to food safety. Here, we assessed linalool's ability to prevent the pellicle of two spoilage B. amyloliquefaciens strains. The minimum biofilm inhibitory concentration (MBIC) of linalool against B. amyloliquefaciens DY1a and DY1b was 4 μL/mL and 8 μL/mL, respectively. The MBIC of linalool had a considerable eradication rate of 77.15% and 83.21% on the biofilm of the two strains, respectively. Scanning electron microscopy observations revealed that less wrinkly and thinner pellicle biofilms formed on a medium supplemented with 1/2 MBIC and 1/4 MBIC linalool. Also, linalool inhibited cell motility and the production of extracellular polysaccharides and proteins of the biofilm matrix. Furthermore, linalool exposure reduced the cell surface hydrophobicity, zeta potential, and cell auto-aggregation of B. amyloliquefaciens. Molecular docking analysis demonstrated that linalool interacted strongly with quorum-sensing ComP receptor and biofilm matrix assembly TasA through intermolecular hydrogen bonds, hydrophobic contacts, and van der Waals forces interacting with site residues. Overall, our findings suggest that linalool may be employed as a potential antibiofilm agent to control food spoilage B. amyloliquefaciens.

Exopolysaccharide from Lactobacillus casei NA-2 attenuates Escherichia coli O157:H7 surface adhesion via modulation of membrane surface properties and adhesion-related gene expression

The natural compound, exopolysaccharide from Lactobacillus casei NA-2 (EPS-cn2), has been shown to inhibit biofilm formation by Escherichia coli O157:H7. Although bacterial adhesion to substrate surfaces is a primary, indispensable step in this process, the mechanisms by which EPS-cn2 can block E. coli O157:H7 adhesion to biotic or abiotic surfaces remain unclear. In this study, investigation of E. coli O157:H7 response to EPS-cn2 revealed that 1 mg/mL EPS-cn2 can decrease adherence to polystyrene and confluent Caco-2 cell surfaces to 49.0% (P＜0.0001) and 57.0% (P＜0.01) of that in untreated E. coli O157:H7, respectively. Moreover, EPS-cn2 significantly reduced outer membrane hydrophobicity by 49.0% and decreased the electronegativity of the membrane surface charge by as much as 1.57 mV (P＜0.05) compared to untreated cells. High throughput RNA sequencing indicated that genes responsible for adhesion through extracellular matrix secretion, such as poly-N-acetyl-glucosamine (PNAG) biosynthesis, locus of enterocyte effacement (LEE) proteins and outer membrane protein (OmpT) were all down-regulated in response to EPS-cn2, while chemotaxis and motility-related flagellar assembly genes were differentially up-regulated, suggesting that the EPS-cn2 may serve as an extracellular signal to attenuate adhesion-related gene expression and alter bacterial surface properties in E. coli O157:H7. These findings support the further development of EPS-cn2 for pathogenic biofilm management in clinical and industrial settings, and suggests the further targeting of adhesion-related genes to limit the persistence of this highly pathogenic strain in sensitive environments.

Transfer of bacteria between fabric and surrogate skin

BACKGROUND

Contaminated textiles serve as fomites in healthcare settings. The extent of transfer of pathogens from fabrics depends on the surface properties of the 2 contact surfaces.

METHODS

In the current study, the effect of surface energy and surface roughness of fabrics on the transfer of Escherichia coli and Staphylococcus aureus to and from textiles to surrogate skin were determined. Three fabrics (100% cotton, 100% polyester, and 50-50 blend of cotton and polyester) having identical constructional parameters, were characterised on the basis of surface roughness, and energy. Assessment of transfer of bacteria was carried out by bringing the matrix seeded with inoculum in contact with the sterilized matrix for a predetermined period of time, followed by dislodging of cells from the recipient surface by vortexing, and plating.

RESULTS AND DISCUSSION

Results showed that 100% polyester attracted the highest number of bacterial cells compared to the others. It also released the maximum number of bacteria upon coming in contact with surrogate skin. Properties of fabrics like absorbency, surface energy, and surface roughness, simultaneously affected transfer.

CONCLUSIONS

It is advisable to minimize the use of 100% polyester in healthcare settings to curb the transfer load of bacteria from one surface to another.

Tea extracts inhibit the attachment of streptococci to oral/dental substrata by reducing hydrogen bonding energies

Previous work in the authors' lab demonstrated that tea extracts significantly suppressed streptococcal colonization of abiotic substrata by coating the bacterial cell surfaces with tea components. In this study, the physico-chemical mechanisms by which the tea coating inhibits cellular attachment are demonstrated. The changes in the cell surface physico-chemical properties of streptococci, induced by tea extracts, were measured. Using these results, surface interaction energies were calculated between streptococcal cells and hard surfaces (glass, stainless steel, hydroxyapatite and titanium) within the cellular attachment system exploiting the extended Derjaguin-Landau-Verwey-Overbeek theory. The net energy outcomes were compared with experiment results of attachment assays to validate the predictability of the model. The results showed that the tea extracts inhibited the attachment of the bacteria by 11.1%-91.5%, and reduced the interaction energy by 15.4%-94.9%. It was also demonstrated that the abilities of the bacteria to attach to hard surfaces correlated well with their net interaction energies. The predominant interaction in the systems was found to be hydrogen bonding. In conclusion, tea extracts suppress streptococcal attachment to hard substrata by limiting the formation of hydrogen bonds.

Microscopic analysis towards rhamnolipid-mediated adhesion of Thiobacillus denitrificans: A QCM-D study

Rhamnolipid was proved to increase the abundance of Thiobacillus denitrificans in the mixotrophic denitrification biofilm while its microscopic mechanism remains to be explored. Effect of rhamnolipids on deposition of macromolecular substances and adhesion of Thiobacillus denitrificans at room (20 °C) and low temperature (10 °C) were systematically investigated by the quartz crystal microbalance with dissipation monitoring (QCM-D) for the first time. Results showed that low concentration of rhamnolipids (20-80 mg/L) could promote the deposition of macromolecular substances by reducing hydraulic repulsion force, with the maximum deposition amount increased by 4.28 times than that of the control at room temperature. Deposition amount of microorganisms could be improved by increasing its concentration at room temperature while it didn't work at low temperature. Meanwhile, low temperature could significantly inhibit adhesion of Thiobacillus denitrificans (p < 0.05) and deposited layers under low concentration of rhamnolipids were generally rigid, resulting in the negative feedback effect on the microorganisms' adhesion. While high concentration of rhamnolipids (120-200 mg/L) could regulate the biofilm from rigid to viscoelastic and significantly promote the initial adhesion of Thiobacillus denitrificans on SiO₂ surface (p < 0.05). This study demonstrated the microscopic mechanism of rhamnolipids on the initial biofilm formation, that is, the reduction of hydration repulsion force was responsible for the enhanced deposition of macromolecules while the regulation of biofilm properties was account for the promoted adhesion of Thiobacillus denitrificans.

Impacts of surface wettability and roughness of styrene-acrylic resin films on adhesion behavior of microalgae Chlorella sp

Biofilm attached cultivation is a promising method for efficient production of microalgae. Determining the surface property index to select an appropriate substrate benefiting the algae adhesion and biofilm formation is very important for the cultivation method. This work focused on elucidating and quantifying the influence of surface wettability and roughness of substrate on Chlorella vulgaris adhesion. Firstly, surface modified styrene-acrylic (SA) resin films by adding different dosage of perfluoroalkyl ethyl acrylate (FM) were prepared. Property characterization shows that the surface contact angle in water, formamide and diiodomethane of FM modified SA films is significantly associated with the FM dosage, while the other surface properties including zeta potential, surface potential and surface roughness have insignificant difference. The calculated surface free energy parameters show that the SA films belong to the non-polar substrata. A well quantitative correlation that the adhesion capacity of C. vulgaris linearly declines with the increase of water contact angle was obtained. And a near linear relationship between the adhesion capacity and the surface free energy (γ), or the cohesion free energy (ΔG_coh) was also observed. Secondly, the surface roughness solely changed SA films were prepared by replicating the morphology of stainless steel sieves through the PDMS template method. The patterned SA films have alternately arranged rectangular "valleys" and "ridges". A well linear correlation between the microalgae adhesion capacity and the surface roughness was also obtained.

Tea extracts modulate oral biofilm development by altering bacterial hydrophobicity and aggregation

OBJECTIVES

This study aims to investigate the effects of tea extracts on biofilm formation by oral streptococci and the potential mechanisms behind the effects.

DESIGN

We examined the effects of five types of tea extracts (green, oolong, black, pu-erh and chrysanthemum tea) on cell surface hydrophobicity and auto-aggregation of three different streptococcal species (Streptococcus mutans, Streptococcus salivarius and Streptococcus mitis) and evaluated their biofilm formation on four disparate hard surfaces (glass, stainless steel, hydroxyapatite and titanium). The correlation between biofilm formation and the cellular properties were investigated in order to study the mechanisms by which the tea extracts affect biofilm formation.

RESULTS

Results show that the tea extracts reduced cell surface hydrophobicity (by up to 57.9 %) and, in some cases, altered cellular auto-aggregation (by up to 12 %) and biofilm formation (by up to 2.61 log CFU cm^-2). Specifically, oolong tea extract was found to enhance biofilm formation by increasing cellular auto-aggregation and pu-erh tea extract retarded biofilm formation by increasing auto-aggregation. Biofilm formation correlated well to cell surface hydrophobicity and auto-aggregation in combination, but not to either one alone as determined by multiple linear regression analysis.

CONCLUSIONS

Tea extracts have the ability to modulate streptococcal biofilm formation by altering cell surface hydrophobicity and cellular aggregation.

Genetic diversity, biofilm and virulence characteristics of Listeria monocytogenes in salmon sushi

Sushi is a ready-to-eat (RTE) food prepared from raw or cooked fish that is widely consumed worldwide. Listeria monocytogenes is the foodborne pathogen most commonly associated with RTE and fish products. The aim of the present study was to evaluate the presence of L. monocytogenes in salmon sushi commercialized in Pelotas city, Brazil, and to evaluate the genetic diversity, biofilm-forming ability in stainless steel, and virulence characteristics of the isolates. Four sampling events were carried out in seven specialized sushi establishments totaling 28 sushi pools. Listeria monocytogenes was detected in six samples (21.4%) from two establishments (28.6%). All isolates belonged to serotype 4b and carried the prfA, plcA, plcB, hlyA, mpl, actA, inlA, inlC, inlJ, and iap genes. The inlB gene was not detected in two isolates. The PFGE analysis grouped the isolates into four pulsotypes. All isolates had the ability to form biofilm on stainless steel and the average of biofilm formation counts varied between 6.4 and 7.2 log CFU.cm^-2. The isolates harbored the biofilm-related genes agrA, agrB, agrC, agrD, and prfA, with the exception of two isolates that did not harbor the agrD gene. The presence of L. monocytogenes in RTE sushi is a concern, demonstrating that sushi consumption may be a risk of human listeriosis. Furthermore, it was possible to identify the persistence of this pathogen for at least one month (pulsotypes III and IV), in two establishments (A and G), highlighting the need for improving the cleaning and sanitation procedures in establishments that commercialize RTE sushi.

Inhibitory effects of saliva as a suspending fluid on attachment of oral bacteria to hydroxyapatite and titanium

OBJECTIVES

This study aims to examine the influence of saliva on the attachment of oral bacteria to hydroxyapatite and titanium surfaces in an in vitro setting using saliva as a suspending fluid for the bacterial cells, and to investigate the changes in bacterial surface physicochemical properties (hydrophobicity and charge) induced by saliva.

DESIGN

Saliva collected from human donors was used to treat five strains of oral bacteria. The surface hydrophobicity and charge of the treated cells were measured. The effects of saliva as a suspending fluid on attachment of the strains to hydroxyapatite and titanium were investigated.

RESULTS

Saliva was found to inhibit the attachment of four streptococcal strains by up to 100-fold. The inhibitory effects were potentially due to changes in cell-surface physicochemical properties induced by saliva. These effects were, however, not observed on Actinomyces naeslundii.

CONCLUSIONS

The results suggest that saliva may reduce bacterial colonization by oral streptococci and that using saliva as a suspending fluid may be a useful addition for bacterial attachment studies.

Epigallocatechin gallate and gallic acid affect colonization of abiotic surfaces by oral bacteria

OBJECTIVES

epigallocatechin gallate and gallic acid are known antimicrobial agents. Their roles in controlling microbial colonization, such as bacterial attachment and biofilm formation, are however not completely clear. This study aims to investigate their effects on the colonization of abiotic surfaces by oral bacteria and study the mechanism of their activities.

DESIGN

the effects of epigallocatechin gallate and gallic acid on cell surface physicochemical properties (hydrophobicity and charge) of a range of oral bacteria and their auto-aggregation, attachment and biofilm formation on different abiotic surfaces (glass, stainless steel and hydroxyapatite) were studied.

RESULTS

results show that epigallocatechin gallate inhibited bacterial attachment to the hard surfaces (except hydroxyapatite) by 0.2-1.4 log CFU cm^-2 by affecting cell surface hydrophobicity and charge. In addition, epigallocatechin gallate induced notches on cell surfaces of Streptococcus mutans without affecting their viability and biofilm formation. Gallic acid enhanced auto-aggregation (by 7.9-30.6 %) and biofilm formation by Actinomyces naeslundii (by 0.9-1.2 log CFU cm^-2) by causing calcium efflux from the cells.

CONCLUSIONS

the tested phytochemicals influenced the colonization of abiotic surfaces by oral bacteria through different mechanisms, most notably via affecting cell surface physicochemical properties, inducing changes in the shape of cell envelopes and causing calcium efflux.

Kouzani A, Mosadegh B, Gharaie S. Blood Pressure Sensors: Materials, Fabrication Methods, Performance Evaluations and Future Perspectives

Advancements in materials science and fabrication techniques have contributed to the significant growing attention to a wide variety of sensors for digital healthcare. While the progress in this area is tremendously impressive, few wearable sensors with the capability of real-time blood pressure monitoring are approved for clinical use. One of the key obstacles in the further development of wearable sensors for medical applications is the lack of comprehensive technical evaluation of sensor materials against the expected clinical performance. Here, we present an extensive review and critical analysis of various materials applied in the design and fabrication of wearable sensors. In our unique transdisciplinary approach, we studied the fundamentals of blood pressure and examined its measuring modalities while focusing on their clinical use and sensing principles to identify material functionalities. Then, we carefully reviewed various categories of functional materials utilized in sensor building blocks allowing for comparative analysis of the performance of a wide range of materials throughout the sensor operational-life cycle. Not only this provides essential data to enhance the materials' properties and optimize their performance, but also, it highlights new perspectives and provides suggestions to develop the next generation pressure sensors for clinical use.

Analysing the Initial Bacterial Adhesion to Evaluate the Performance of Antifouling Surfaces

The aim of this work was to study the initial events of Escherichia coli adhesion to polydimethylsiloxane, which is critical for the development of antifouling surfaces. A parallel plate flow cell was used to perform the initial adhesion experiments under controlled hydrodynamic conditions (shear rates ranging between 8 and 100/s), mimicking biomedical scenarios. Initial adhesion studies capture more accurately the cell-surface interactions as in later stages, incoming cells may interact with the surface but also with already adhered cells. Adhesion rates were calculated and results shown that after some time (between 5 and 9 min), these rates decreased (by 55% on average), from the initial values for all tested conditions. The common explanation for this decrease is the occurrence of hydrodynamic blocking, where the area behind each adhered cell is screened from incoming cells. This was investigated using a pair correlation map from which two-dimensional histograms showing the density probability function were constructed. The results highlighted a lower density probability (below 4.0 × 10⁻⁴) of the presence of cells around a given cell under different shear rates irrespectively of the radial direction. A shadowing area behind the already adhered cells was not observed, indicating that hydrodynamic blocking was not occurring and therefore it could not be the cause for the decreases in cell adhesion rates. Afterward, cell transport rates from the bulk solution to the surface were estimated using the Smoluchowski-Levich approximation and values in the range of 80–170 cells/cm².s were obtained. The drag forces that adhered cells have to withstand were also estimated and values in the range of 3–50 × 10⁻¹⁴ N were determined. Although mass transport increases with the flow rate, drag forces also increase and the relative importance of these factors may change in different conditions. This work demonstrates that adjustment of operational parameters in initial adhesion experiments may be required to avoid hydrodynamic blocking, in order to obtain reliable data about cell-surface interactions that can be used in the development of more efficient antifouling surfaces.

Streptococcus mutans adhesion force sensing in multi-species oral biofilms

Bacteria utilize chemical and mechanical mechanisms to sense their environment, to survive hostile conditions. In mechanical sensing, intra-bilayer pressure profiles change due to deformation induced by the adhesion forces bacteria experience on a surface. Emergent properties in mono-species Streptococcus mutans biofilms, such as extracellular matrix production, depend on the adhesion forces that streptococci sense. Here we determined whether and how salivary-conditioning film (SCF) adsorption and the multi-species nature of oral biofilm influence adhesion force sensing and associated gene expression by S. mutans. Hereto, Streptococcus oralis, Actinomyces naeslundii, and S. mutans were grown together on different surfaces in the absence and presence of an adsorbed SCF. Atomic force microscopy and RT-qPCR were used to measure S. mutans adhesion forces and gene expressions. Upon SCF adsorption, stationary adhesion forces decreased on a hydrophobic and increased on a hydrophilic surface to around 8 nN. Optical coherence tomography showed that triple-species biofilms on SCF-coated surfaces with dead S. oralis adhered weakly and often detached as a contiguous sheet. Concurrently, S. mutans displayed no differential adhesion force sensing on SCF-coated surfaces in the triple-species biofilms with dead S. oralis, but once live S. oralis were present S. mutans adhesion force sensing and gene expression ranked similar as on surfaces in the absence of an adsorbed SCF. Concluding, live S. oralis may enzymatically degrade SCF components to facilitate direct contact of biofilm inhabitants with surfaces and allow S. mutans adhesion force sensing of underlying surfaces to define its appropriate adaptive response. This represents a new function of initial colonizers in multi-species oral biofilms.

Effect of surface characteristics on the antibacterial properties of titanium dioxide nanotubes produced in aqueous electrolytes with carboxymethyl cellulose

Nanotubular structures were produced on a commercially pure titanium surface by anodization in an aqueous electrolyte that contained carboxymethyl cellulose and sodium fluoride. The internal diameters obtained were about 100, 48, and 9.5 nm, respectively. Several heat treatments at 200, 350, and 600°C were made to produce nanotubes with different titanium dioxide polymorphs (anatase, rutile). All tested surfaces were superhydrophilic, this behavior was maintained after at least 30 days, regardless of the heat treatment. Although in previous works the nanotube features effect on the bacteria behavior had been studied; this item still unclear. For the best of our knowledge, the effect of small internal diameters (about 10 nm) with and without heat treatment and with and without ultraviolet (UV) irradiation on the bacteria strains comportment has not been reported. From our results, both the internal diameter and the postanodized treatments have an effect on the bacteria strains comportment. All nanotubular coatings UV treated and heat treated at 350 and 600°C; despite they have different inner diameters, inhibit the bacteria growth of both Staphylococcus aureus and Pseudomonas aeruginosa strains. The nanotubular coatings obtained at 20 V and heat treated at 350°C produced the lower bacteria adhesion against both strains evaluated.

Reduced bacterial adhesion on zirconium-based bulk metallic glasses by femtosecond laser nanostructuring

As high-performing materials, bulk metallic glasses have attracted widespread attention for biomedical applications. Herein, the bacterial adhesion properties of femtosecond laser-nanostructured surfaces of four types of zirconium-based bulk metallic glasses are assessed. Laser-induced periodical surface structures and nanoparticle structures were fabricated by femtosecond laser irradiation under different energy intensities (0.23 and 2.3 J/mm2). Surface topography, roughness, wettability, and surface energy were investigated after femtosecond laser irradiation and the surface bacterial adhesion properties were explored using Escherichia coli and Staphylococcus aureus as respective representatives of Gram-negative and Gram-positive bacteria. 4',6-Diamidino-2-phenylindole fluorescence staining was used to characterize and assess the bacterial surface coverage rate. The in vitro cytotoxicity of polished and laser-nanostructured surfaces was investigated using MC3T3-E cells. The obtained results demonstrate that femtosecond laser surface nanostructuring retained the amorphous structure of zirconium-based bulk metallic glasses and led to an obvious decrease in bacterial adhesion compared with polished surfaces. The inhibition of bacterial adhesion on laser-induced periodical surface structures was greater than on nanostructured surfaces after 24 h of bacterial incubation. In addition, femtosecond laser nanostructuring did not have an apparent effect on the cytotoxicity of zirconium-based bulk metallic glasses.

Quercetin repressed the stress response factor (sigB) and virulence genes (prfA, actA, inlA, and inlC), lower the adhesion, and biofilm development of L. monocytogenes

The present study explored the effect of quercetin on the expression of virulence genes actA, inlA, inlC, and their regulatory components, sigB and prfA, in L. monocytogenes. Furthermore, the physicochemical changes on the surface, membrane permeability, and biofilm formation of quercetin-treated bacteria were evaluated. An inhibitory dose-dependent effect of quercetin (0.1-0.8 mM) was observed on the cell attachment on stainless steel at 2 and 6 h at 37 °C. Quercetin at 0.8 mM prevented the biofilm formation on stainless steel surfaces after 6 h of incubation at 37 °C, while the untreated bacteria formed biofilms with a cell density of 5.1 Log CFU/cm². The microscopic analysis evidenced that quercetin at 0.2 mM decreased the biovolume and covered area of the attached micro-colonies. Also, sigB, prfA, inlA, inlC, and actA genes were downregulated by 7-29 times lower compared to untreated bacteria. In addition, quercetin decreased the superficial cell charge, increased the membrane permeability, and its surface hydrophobicity. These results demonstrated that quercetin prevented biofilm formation, repressed the genes of stress and virulence of L. monocytogenes and also altered the physicochemical cell properties.

Bacterial Density and Biofilm Structure Determined by Optical Coherence Tomography

Optical-coherence-tomography (OCT) is a non-destructive tool for biofilm imaging, not requiring staining, and used to measure biofilm thickness and putative comparison of biofilm structure based on signal intensity distributions in OCT-images. Quantitative comparison of biofilm signal intensities in OCT-images, is difficult due to the auto-scaling applied in OCT-instruments to ensure optimal quality of individual images. Here, we developed a method to eliminate the influence of auto-scaling in order to allow quantitative comparison of biofilm densities in different images. Auto- and re-scaled signal intensities could be qualitatively interpreted in line with biofilm characteristics for single and multi-species biofilms of different strains and species (cocci and rod-shaped organisms), demonstrating qualitative validity of auto- and re-scaling analyses. However, specific features of pseudomonas and oral multi-species biofilms were more prominently expressed after re-scaling. Quantitative validation was obtained by relating average auto- and re-scaled signal intensities across biofilm images with volumetric-bacterial-densities in biofilms, independently obtained using enumeration of bacterial numbers per unit biofilm volume. The signal intensities in auto-scaled biofilm images did not significantly relate with volumetric-bacterial-densities, whereas re-scaled intensities in images of biofilms of widely different strains and species increased linearly with independently determined volumetric-bacterial-densities in the biofilms. Herewith, the proposed re-scaling of signal intensity distributions in OCT-images significantly enhances the possibilities of biofilm imaging using OCT.

Analyzing the effect of pH on microalgae adhesion by identifying the dominant interaction between cell and surface

Microalgae adhesion plays a critical role in developing effective photobioreactors for large-scale production of microalgae biofuel. This study focused on elucidating the influencing mechanism of liquid medium pH on microalgae adhesion by identifying the dominant interactions between cell and substratum using a criterion. Herein, the adhesion of three microalgae onto two substrata at a series of pH was observed using a flow chamber. The results indicated that the adhesion of freshwater Chlorella sp. onto PVC and glass and marine Chlorella sp. and N. oculata onto glass decreased with increasing pH, because these adhesions were dominated by the EL interaction, and the pH would influence the adhesion primarily by affecting the ζ potential of the cell and substratum. Whereas, the adhesion of marine Chlorella sp. and N. oculata onto PVC increased with increasing pH, because these adhesions were dominated by Lewis acid-base (AB) interaction, and the pH would influence the adhesion primarily by affecting the components of surface free energy of cell. The study demonstrated that the influencing mechanism of pH on adhesion can be conclusively elucidated by identifying the dominant interaction between the cell and the surface, and may have significant implications for predicting cell adhesion in various applications.

Evaluating Efficacy of Antimicrobial and Antifouling Materials for Urinary Tract Medical Devices: Challenges and Recommendations

In Europe, the mean incidence of urinary tract infections in intensive care units is 1.1 per 1000 patient-days. Of these cases, catheter-associated urinary tract infections (CAUTI) account for 98%. In total, CAUTI in hospitals is estimated to give additional health-care costs of £1-2.5 billion in the United Kingdom alone. This is in sharp contrast to the low cost of urinary catheters and emphasizes the need for innovative products that reduce the incidence rate of CAUTI. Ureteral stents and other urinary-tract devices suffer similar problems. Antimicrobial strategies are being developed, however, the evaluation of their efficacy is very challenging. This review aims to provide considerations and recommendations covering all relevant aspects of antimicrobial material testing, including surface characterization, biocompatibility, cytotoxicity, in vitro and in vivo tests, microbial strain selection, and hydrodynamic conditions, all in the perspective of complying to the complex pathology of device-associated urinary tract infection. The recommendations should be on the basis of standard assays to be developed which would enable comparisons of results obtained in different research labs both in industry and in academia, as well as provide industry and academia with tools to assess the antimicrobial properties for urinary tract devices in a reliable way.

Quantitative Criterion to Predict Cell Adhesion by Identifying Dominant Interaction between Microorganisms and Abiotic Surfaces

Cell adhesion is ubiquitous and plays an important role in various scientific and engineering problems. Herein, a quantitative criterion to predict cell adhesion was proposed by identifying the dominant interaction between microorganisms and abiotic surfaces. According to the criterion, the dominant interaction in cell adhesion could be identified as a Lewis acid-base (AB) interaction or electrostatic (EL) interaction via comparison of two expressions containing the electron-donor characteristics of the microorganism (γ_mv^-) and abiotic surface (γ_sv^-) and their ζ potentials (ζ_m, ζ_s). The results revealed that when dominated by the AB interaction, adhesion would decrease with increasing [Formula: see text]. However, when the EL interaction was dominant, adhesion would decrease with increasing (ζ_m + ζ_s)². We have verified the criterion based on the adhesion of microalgae, bacteria, and fungi onto various surfaces obtained via our experiments and available in literature studies. The results demonstrated that the criterion had important implications in the prediction of cell adhesion in various applications.

Skin surface physico-chemistry: Characteristics, methods of measurement, influencing factors and future developments

Physico-chemical properties such as surface free energy, polarity or hydrophobicity of solid surfaces have been largely studied in literature because they are involved in many physical phenomena: adhesion, friction, wetting … Nowadays, the study of biointerfaces is of great interest for the medical, the pharmaceutical or the cosmetic field but also for material design researches, especially for the development of biomimetic surfaces. The present paper focuses on a particular biointerface, namely skin, which is the most extended organ of the human body. The different ways for the study of skin physico-chemistry are first reviewed, followed by their practical uses, from pharmaceutical to cosmetic science. Those properties depict the ways skin interacts with topical products, its lipid composition but also its hydration state. In addition, this article aims to present recent approaches using original model materials in order to mimic human skin; indeed, in vivo experiments are often limited by the inter and intra individual variability, the safety regulation and above all the time and the cost of such studies. Finally, further data clearly highlight the importance of skin surface properties for dermatological and pharmaceutical researches.

No wisdom in the crowd: genome annotation in the era of big data - current status and future prospects

Science and engineering rely on the accumulation and dissemination of knowledge to make discoveries and create new designs. Discovery-driven genome research rests on knowledge passed on via gene annotations. In response to the deluge of sequencing big data, standard annotation practice employs automated procedures that rely on majority rules. We argue this hinders progress through the generation and propagation of errors, leading investigators into blind alleys. More subtly, this inductive process discourages the discovery of novelty, which remains essential in biological research and reflects the nature of biology itself. Annotation systems, rather than being repositories of facts, should be tools that support multiple modes of inference. By combining deduction, induction and abduction, investigators can generate hypotheses when accurate knowledge is extracted from model databases. A key stance is to depart from 'the sequence tells the structure tells the function' fallacy, placing function first. We illustrate our approach with examples of critical or unexpected pathways, using MicroScope to demonstrate how tools can be implemented following the principles we advocate. We end with a challenge to the reader.