Alumina surfaces with nanoscale topography reduce attachment and biofilm formation by Escherichia coli and Listeria spp

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.

Nanotopography and oral bacterial adhesion on titanium surfaces: in vitro and in vivo studies

The present study aimed to evaluate the influence of titanium surface nanotopography on the initial bacterial adhesion process by in vivo and in vitro study models. Titanium disks were produced and characterized according to their surface topography: machined (Ti-M), microtopography (Ti-Micro), and nanotopography (Ti-Nano). For the in vivo study, 18 subjects wore oral acrylic splints containing 2 disks from each group for 24 h (n = 36). After this period, the disks were removed from the splints and evaluated by microbial culture method, scanning electron microscopy (SEM), and qPCR for quantification of Streptococcus oralis, Actinomyces naeslundii, Fusobacterium nucleatum, as well as total bacteria. For the in vitro study, adhesion tests were performed with the species S. oralis and A. naeslundii for 24 h. Data were compared by ANOVA, with Tukey's post-test. Regarding the in vivo study, both the total aerobic and total anaerobic bacteria counts were similar among groups (p > 0.05). In qPCR, there was no difference among groups of bacteria adhered to the disks (p > 0.05), except for A. naeslundii, which was found in lower proportions in the Ti-Nano group (p < 0.05). In the SEM analysis, the groups had a similar bacterial distribution, with a predominance of cocci and few bacilli. In the in vitro study, there was no difference in the adhesion profile for S. oralis and A. naeslundii after 24 h of biofilm formation (p > 0.05). Thus, we conclude that micro- and nanotopography do not affect bacterial adhesion, considering an initial period of biofilm formation.

Factors influencing initial bacterial adhesion to antifouling surfaces studied by single-cell force spectroscopy

Biofilm formation, a major concern for healthcare systems, is initiated when bacteria adhere to surfaces. Escherichia coli adhesion is mediated by appendages, including type-1 fimbriae and curli amyloid fibers. Antifouling surfaces prevent the adhesion of bacteria to combat biofilm formation. Here, we used single-cell force-spectroscopy to study the interaction between E. coli and glass or two antifouling surfaces: the tripeptide DOPA-Phe(4F)-Phe(4F)-OMe and poly(ethylene glycol) polymer-brush. Our results indicate that both antifoulants significantly deter E. coli initial adhesion. By using two mutant strains expressing no type-1 fimbriae or curli amyloids, we studied the adhesion mechanism. Our results suggest that the bacteria adhere to different antifoulants via separate mechanisms. Finally, we show that some bacteria adhere much better than others, illustrating how the variability of bacterial cultures affects biofilm formation. Our results emphasize how additional study at the single-cell level can enhance our understanding of bacterial adhesion, thus leading to novel antifouling technologies.

Impact of nanoscale silicon dioxide coating of stainless-steel surfaces on Listeria monocytogenes

High resistance to environmental factors as well as the ability to form biofilms allow Listeria monocytogenes to persist for a long time in difficult-to-reach places in food-producing plants. L. monocytogenes enters final products from contaminated surfaces in different areas of plants and poses a health risk to consumer. Modified surfaces are already used in the food industry to prevent cross-contamination. In this study, stainless-steel surfaces were coated with nanoscale silicon dioxide and the effects on attachment, bacterial growth and detachment of L. monocytogenes were evaluated. Attachment was considered for three different ways of application to simulate different scenarios of contamination. Bacterial growth of L. monocytogenes on the surface was recorded over a period of up to 8 h. Detachment was tested after cleaning inoculated stainless-steel surfaces with heated distilled water or detergent. Coating stainless-steel surfaces with nanoscale silica tends to reduce adherence and increased detachment and does not influence the bacterial growth of L. monocytogenes. Further modifications of the coating are necessary for a targeted use in the reduction of L. monocytogenes in food-processing plants.

Microbial investigation of cleanability of different plastic and metal surfaces used by the food industry

Different conveyor belt materials used by the meat and other food industries were compared, regarding their cleanability as bacterial reduction rates in relation to their surface topography. Eleven thermoplastic polymers, four stainless steels, and five aluminized nanostructured surfaces were investigated under laboratory conditions. Cleanings were conducted with water only, and with an alkaline foam detergent. Overall, scanning electron microscopy revealed remarkable differences in the surface topography of the tested surfaces. Water cleaning results showed that nanostructured aluminized surfaces achieved significantly higher cleanability rates compared to the eight thermoplastic surfaces, as well as the glass-bead blasted rough stainless steel. Thermoplastic surfaces showed overall low cleanability rates when cleaned with alkaline detergent, while stainless steel and nanoporous aluminum showed high variations. Overall, nanoporous aluminum showed promising results as it can be used to coat conveyor belts. However, compatibility with cleaning detergent and sensitivity to scratches must be further investigated. Overall, it can be concluded that cleanability is not only influenced by surface roughness, but also by the overall surface finish, scratches, and defects.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05778-0.

Blue 405 nm LED light effectively inactivates bacterial pathogens on substrates and packaging materials used in food processing

This study investigates the antimicrobial effectiveness of 405 nm light emitting diodes (LEDs) against pathogenic Escherichia coli O157:H7, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium, and Staphylococcus aureus, in thin liquid films (TLF) and on solid surfaces. Stainless steel (SS), high density polyethylene (HDPE), low density polyethylene (LDPE), and borosilicate glass were used as materials typically encountered in food processing, food service, and clinical environments. Anodic aluminum oxide (AAO) coupons with nanoscale topography were used, to evaluate the effect of topography on inactivation. The impact of surface roughness, hydrophobicity, and reflectivity on inactivation was assessed. A 48 h exposure to 405 nm led to reductions ranging from 1.3 (E. coli) to 5.7 (S. aureus) log CFU in TLF and 3.1 to 6.3 log CFU on different solid contact surfaces and packaging materials. All inactivation curves were nonlinear and followed Weibull kinetics, with better inactivation predictions on surfaces (0.89 ≤ R2 ≤ 1.0) compared to TLF (0.76 ≤ R2 ≤ 0.99). The fastest inactivation rate was observed on small nanopore AAO coupons inoculated with L. monocytogenes and S. aureus, indicating inactivation enhancing potential of these surfaces. These results demonstrate significant promise of 405 nm LEDs for antimicrobial applications in food processing and handling and the healthcare industry.

Textiles as fomites in the healthcare system

Nosocomial infections or healthcare-associated infections (HAIs) are acquired under medical care in healthcare facilities. In hospital environments, the transmission of infectious diseases through textiles such as white coats, bed linen, curtains, and towels are well documented. Textile hygiene and infection control measures have become more important in recent years due to the growing concerns about textiles as fomites in healthcare settings. However, systematic research in this area is lacking; the factors contributing to the transmission of infections through textiles needs to be better understood. The review aims to critically explore textiles as contaminants in healthcare systems, and to identify potential risks they may pose to patients and healthcare workers. It delineates different factors affecting bacterial adherence on fabrics, such as surface properties of bacteria and fabrics, and environmental factors. It also identifies areas that require further research to reduce the risk of HAIs and improve textile hygiene practices. Finally, the review elaborates on the strategies currently employed, and those that can be employed to limit the spread of nosocomial infections through fabrics. Implementing textile hygiene practices effectively in healthcare facilities requires a thorough analysis of factors affecting fabric-microbiome interactions, followed by designing newer fabrics that discourage pathogen load. KEY POINTS: • Healthcare textiles act as a potential reservoir of nosocomial pathogens • Survival of pathogens is affected by surface properties of fabric and bacteria • Guidelines required for fabrics that discourage microbial load, for hospital use.

Design of silicone interfaces with antibacterial properties

Silicone implants are widely used for plastic or reconstruction medical applications. However, they can cause severe infections of inner tissues due to bacterial adhesion and biofilm growth on implant surfaces. The development of new antibacterial nanostructured surfaces can be considered as the most promising strategy to deal with this problem. In this article, we studied the influence of nanostructuring parameters on the antibacterial properties of silicone surfaces. Nanostructured silicone substrates with nanopillars of various dimensions were fabricated using a simple soft lithography technique. Upon testing of the obtained substrates, we identified the optimal parameters of silicone nanostructures to achieve the most pronounced antibacterial effect against the bacterial culture of Escherichia coli. It was demonstrated that up to 90% reduction in bacterial population compared to flat silicone substrates can be achieved. We also discussed possible underlying mechanisms behind the observed antibacterial effect, the understanding of which is essential for further progress in this field.

Mechano-Bactericidal Surfaces: Mechanisms, Nanofabrication, and Prospects for Food Applications

Mechano-bactericidal (MB) nanopatterns have the ability to inactivate bacterial cells by rupturing cellular envelopes. Such biocide-free, physicomechanical mechanisms may confer lasting biofilm mitigation capability to various materials encountered in food processing, packaging, and food preparation environments. In this review, we first discuss recent progress on elucidating MB mechanisms, unraveling property-activity relationships, and developing cost-effective and scalable nanofabrication technologies. Next, we evaluate the potential challenges that MB surfaces may face in food-related applications and provide our perspective on the critical research needs and opportunities to facilitate their adoption in the food industry.

Anodized Nanostructured 316L Stainless Steel Enhances Osteoblast Functions and Exhibits Anti-Fouling Properties

Poor osseointegration and infection are among the major challenges of 316L stainless steel (SS) implants in orthopedic applications. Surface modifications to obtain a nanostructured topography seem to be a promising method to enhance cellular interactions of 316L SS implants. In this study, arrays of nanodimples (NDs) having controlled feature sizes between 25 and 250 nm were obtained on 316L SS surfaces by anodic oxidation (anodization). Results demonstrated that the fabrication of NDs increased the surface area and, at the same time, altered the surface chemistry of 316L SS to provide chromium oxide- and hydroxide-rich surface oxide layers. In vitro experiments showed that ND surfaces promoted up to a 68% higher osteoblast viability on the fifth day of culture. Immunofluorescence images confirmed a well-spread cytoskeleton organization on the ND surfaces. In addition, higher alkaline phosphate activity and calcium mineral synthesis were observed on the ND surfaces compared to non-anodized 316L SS. Furthermore, a 71% reduction in Staphylococcus aureus (S. aureus) and a 58% reduction in Pseudomonas aeruginosa (P. aeruginosa) colonies were observed on the ND surfaces having a 200 nm feature size compared to non-anodized surfaces at 24 h of culture. Cumulatively, the results showed that a ND surface topography fabricated on 316L SS via anodization upregulated the osteoblast viability and functions while preventing S. aureus and P. aeruginosa biofilm synthesis.

Antibacterial features of material surface: strong enough to serve as antibiotics?

Bacteria are small but need big efforts to control. The use of antibiotics not only produces superbugs that are increasingly difficult to inactivate, but also raises environmental concerns with the growing consumption. It is now believed that the antibacterial task can count on some physiochemical features of material surfaces, which can be anti-adhesive or bactericidal without releasing toxicants. It is necessary to evaluate to what extent can we rely on the surface design since the actual application scenarios will need the antibacterial performance to be sharp, robust, environmentally friendly, and long-lasting. Herein, we review the recent laboratory advances that have been classified based on the specific surface features, including hydrophobicity, charge potential, micromorphology, stiffness and viscosity, and photoactivity, and the antibacterial mechanisms of each feature are included to provide a basic rationale for future design. The significance of anti-biofilms is also introduced, given the big role of biofilms in bacteria-caused damage. A perspective on the potential wide application of antibacterial surface features as a substitute or supplement to antibiotics is then discussed. Surface design is no doubt a solution worthy to explore, and future success will be a result of further progress in multiple directions, including mechanism study and material preparation.

Antibacterial Activity of Silver and Gold Particles Formed on Titania Thin Films

Metal-based nanoparticles with antimicrobial activity are gaining a lot of attention in recent years due to the increased antibiotics resistance. The development and the pathogenesis of oral diseases are usually associated with the formation of bacteria biofilms on the surfaces; therefore, it is crucial to investigate the materials and their properties that would reduce bacterial attachment and biofilm formation. This work provides a systematic investigation of the physical-chemical properties and the antibacterial activity of TiO2 thin films decorated by Ag and Au nanoparticles (NP) against Veillonella parvula and Neisseria sicca species associated with oral diseases. TiO2 thin films were formed using reactive magnetron sputtering by obtaining as-deposited amorphous and crystalline TiO2 thin films after annealing. Au and Ag NP were formed using a two-step process: magnetron sputtering of thin metal films and solid-state dewetting. The surface properties and crystallographic nature of TiO2/NP structures were investigated by SEM, XPS, XRD, and optical microscopy. It was found that the higher thickness of Au and Ag thin films results in the formation of the enlarged NPs and increased distance between them, influencing the antibacterial activity of the formed structures. TiO2 surface with AgNP exhibited higher antibacterial efficiency than Au nanostructured titania surfaces and effectively reduced the concentration of the bacteria. The process of the observation and identification of the presence of bacteria using the deep learning technique was realized.

Physicochemical Properties of Dentine Subjected to Microabrasive Blasting and Its Influence on Bonding to Self-Adhesive Prosthetic Cement in Shear Bond Strength Test: An In Vitro Study

The aim of this in vitro study was to assess the influence of microabrasive blasting on the physicochemical properties of dentine and shear bond strength (SBS) of self-adhesive resin cement (Maxcem Elite, Kerr, Orange, CA, USA) bonded to the dentine surface. Ninety cylindrical specimens with exposed dentine of human teeth were prepared and divided into three randomized, parallel sample sets A, B, and C. Groups B and C were subjected to abrasive blasting using a micro-sandblasting device (Microetcher IIa, Danville Materials, Carlsbad, CA, USA) with two gradations of Al₂O₃ abrasives (Group B, abrasion with a gradation of 50 μm; group C, abrasion with a gradation of 27 μm). SEM imaging, profilometry, chemical composition analysis, contact angle measurements, surface free energy, and SBS tests were performed. The resulting data were statistically analyzed using the Statistica software (ver. 13.3, Tibco Software Inc., Palo Alto, CA, USA). Microabrasive blasting caused changes in surface topography, structural features, and the connection strength between the dentin surface and self-adhesive prosthetic cement. Air microabrasion through the multifactorial positive reorganization of the treated surface of dentine is recommended as a pretreatment method in fixed prosthodontics adhesive cementation protocols.

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.

Engineered topographies and hydrodynamics in relation to biofouling control-a review

Biofouling, the unwanted growth of microorganisms on submerged surfaces, has appeared as a significant impediment for underwater structures, water vessels, and medical devices. For fixing the biofouling issue, modification of the submerged surface is being experimented as a non-toxic approach worldwide. This technique necessitated altering the surface topography and roughness and developing a surface with a nano- to micro-structured pattern. The main objective of this study is to review the recent advancements in surface modification and hydrodynamic analysis concerning biofouling control. This study described the occurrence of the biofouling process, techniques suitable for biofouling control, and current state of research advancements comprehensively. Different biofilms under various hydrodynamic conditions have also been outlined in this study. Scenarios of biomimetic surfaces and underwater super-hydrophobicity, locomotion of microorganisms, nano- and micro-hydrodynamics on various surfaces around microorganisms, and material stiffness were explained thoroughly. The review also documented the approaches to inhibit the initial settlement of microorganisms and prolong the subsequent biofilm formation process for patterned surfaces. Though it is well documented that biofouling can be controlled to various degrees with different nano- and micro-structured patterned surfaces, the understanding of the underlying mechanism is still imprecise. Therefore, this review strived to present the possibilities of implementing the patterned surfaces as a physical deterrent against the settlement of fouling organisms and developing an active microfluidic environment to inhibit the initial bacterial settlement process. In general, microtopography equivalent to that of bacterial cells influences attachment via hydrodynamics, topography-induced cell placement, and air-entrapment, whereas nanotopography influences physicochemical forces through macromolecular conditioning.

Time-Course Study of the Antibacterial Activity of an Amorphous SiOxCyHz Coating Certified for Food Contact

One of the most-used food contact materials is stainless steel (AISI 304L or AISI 316L), owing to its high mechanical strength, cleanability, and corrosion resistance. However, due to the presence of minimal crevices, stainless-steel is subject to microbial contamination with consequent significant reverb on health and industry costs due to the lack of effective reliability of sanitizing agents and procedures. In this study, we evaluated the noncytotoxic effect of an amorphous SiO_xC_yH_z coating deposited on stainless-steel disks and performed a time-course evaluation for four Gram-negative bacteria and four Gram-positive bacteria. A low cytotoxicity of the SiO_xC_yH_z coating was observed; moreover, except for some samples, a five-logarithm decrease was visible after 1 h on coated surfaces without any sanitizing treatment and inoculated with Gram-negative and Gram-positive bacteria. Conversely, a complete bacterial removal was observed after 30 s⁻¹ min application of alcohol and already after 15 s under UVC irradiation against both bacterial groups. Moreover, coating deposition changed the wetting behaviors of treated samples, with contact angles increasing from 90.25° to 113.73°, realizing a transformation from hydrophilicity to hydrophobicity, with tremendous repercussions in various technological applications, including the food industry.

Tuning surface topographies on biomaterials to control bacterial infection

Microbial contamination and subsequent formation of biofilms frequently cause failure of surgical implants and a good understanding of the bacteria-surface interactions is vital to the design and safety of biomaterials. In this review, the physical and chemical factors that are involved in the various stages of implant-associated bacterial infection are described. In particular, topographical modification strategies that have been employed to mitigate bacterial adhesion via topographical mechanisms are summarized and discussed comprehensively. Recent advances have improved our understanding about bacteria-surface interactions and have enabled biomedical engineers and researchers to develop better and more effective antibacterial surfaces. The related interdisciplinary efforts are expected to continue in the quest for next-generation medical devices to attain the ultimate goal of improved clinical outcomes and reduced number of revision surgeries.

Structure and shelf stability of milk protein gels created by pressure-assisted enzymatic gelation

In this work, pressure-assisted enzymatic gelation was applied to milk proteins, with the goal of enhancing the structure and stability of pressure-created milk protein gels. High-pressure processing (HPP) at 600 MPa, 3 min, and 5°C was applied to milk protein concentrate (MPC) samples of 12.5% protein concentration, both in the absence and in the presence of calf chymosin [up to 60 IMCU (international milk-clotting units)/kg of milk] or camel chymosin (up to 45 IMCU/kg of milk). Gel hardness, water-holding capacity, and degree of proteolysis were used to assess network strength and shelf stability. The processing trials and all measurements were conducted in triplicate. Statistical analyses of the data were performed by ANOVA, at a 95% confidence level. After HPP treatment, we observed significant structural changes for all samples. Pressurization of MPC, with or without chymosin addition, led to extensive protein aggregation and network formation. The strength of HPP-created milk protein gels without chymosin addition, as measured by the elastic modulus (G'), had a value of 2,242 Pa. The value of G' increased with increasing chymosin concentration, reaching as high as 4,800 Pa for samples with 45 IMCU/kg of camel chymosin. During 4 wk of refrigerated storage, the HPP and chymosin MPC gels maintained higher gel hardness and better structural stability compared with HPP only (no chymosin) MPC gels. The water-holding capacity of the gels without chymosin remained at 100% during 28 d of refrigerated storage. The HPP and chymosin MPC gels had a lower water-holding capacity (91-94%) than the HPP-only counterparts, but their water-holding capacity did not decrease during storage. Overall, these findings demonstrate that controlled, fast structural modification of high-concentration protein systems can be obtained by HPP-assisted enzymatic treatment, and the created gels have a strong, stable network. This study provides insights into the possibility of using HPP for the development of milk-protein-based products with novel structures and textures and long refrigerated shelf life, along with the built-in safety imparted by the HPP treatment.

High-pressure structuring of milk protein concentrate: Effect of pH and calcium

In this study, we investigated the effect of pH and calcium on the structural properties of gels created by high-pressure processing (HPP, 600 MPa, 5°C, 3 min) of milk protein concentrate (MPC, 12.5% protein). The pH level of the MPC was varied between 6.6 and 5.1 by adding glucono-δ-lactone (GDL), and the calcium content was varied from 24 to 36 mg of Ca/g of protein by adding calcium chloride. The rheological properties and microstructure of the pressure-treated MPC were assessed. The pressurization treatments and analytical testing were conducted in triplicate. Data were analyzed statistically using one-way ANOVA with Tukey's honestly significant difference post hoc tests. A pressurization time of 3 min was sufficient to induce gel formation in MPC at pH 6.6, so it was used throughout the study. Adjusting either pH or calcium affected the structure of the HPP-created milk protein gels, likely by influencing electrostatic interactions and shifting the calcium-phosphate balance. Gels were formed after pressurization of MPC at pH above 5.3, and increasing the pH from 5.3 to 6.6 resulted in stronger gels with higher values of elastic moduli (G'). At neutral pH (6.6), adding calcium to MPC further increased G'. Scanning electron microscopy showed that reducing pH or adding calcium resulted in more porous, aggregated microstructures. These findings demonstrate the potential of HPP to create a variety of structures using MPC, facilitating a new pathway from dairy protein ingredients to novel, gel-based, high-protein foods, such as puddings or on-the-go protein bars.

Hydrodynamics and surface properties influence biofilm proliferation

A biofilm is an interface-associated colloidal dispersion of bacterial cells and excreted polymers in which microorganisms find protection from their environment. Successful colonization of a surface by a bacterial community is typically a detriment to human health and property. Insight into the biofilm life-cycle provides clues on how their proliferation can be suppressed. In this review, we follow a cell through the cycle of attachment, growth, and departure from a colony. Among the abundance of factors that guide the three phases, we focus on hydrodynamics and stratum properties due to the synergistic effect such properties have on bacteria rejection and removal. Cell motion, whether facilitated by the environment via medium flow or self-actuated by use of an appendage, drastically improves the survivability of a bacterium. Once in the vicinity of a stratum, a single cell is exposed to near-surface interactions, such as van der Waals, electrostatic and specific interactions, similarly to any other colloidal particle. The success of the attachment and the potential for detachment is heavily influenced by surface properties such as material type and topography. The growth of the colony is similarly guided by mainstream flow and the convective transport throughout the biofilm. Beyond the growth phase, hydrodynamic traction forces on a biofilm can elicit strongly non-linear viscoelastic responses from the biofilm soft matter. As the colony exhausts the means of survival at a particular location, a set of trigger signals activates mechanisms of bacterial release, a life-cycle phase also facilitated by fluid flow. A review of biofilm-relevant hydrodynamics and startum properties provides insight into future research avenues.

Bacteria Adhesion of Textiles Influenced by Wettability and Pore Characteristics of Fibrous Substrates

Bacteria adhesion on the surface is an initial step to create biofouling, which may lead to a severe infection of living organisms and humans. This study is concerned with investigating the textile properties including wettability, porosity, total pore volume, and pore size in association with bacteria adhesion. As model bacteria, Gram-negative, rod-shaped Escherichia coli and the Gram-positive, spherical-shaped Staphylococcus aureus were used to analyze the adhesion tendency. Electrospun webs made from polystyrene and poly(lactic acid) were used as substrates, with modification of wettability by the plasma process using either O2 or C4F8 gas. The pore and morphological characteristics of fibrous webs were analyzed by the capillary flow porometer and scanning electron microscopy. The substrate's wettability appeared to be the primary factor influencing the cell adhesion, where the hydrophilic surface resulted in considerably higher adhesion. The pore volume and the pore size, rather than the porosity itself, were other important factors affecting the bacteria adherence and retention. In addition, the compact spatial distribution of fibers limited the cell intrusion into the pores, reducing the total amount of adherence. Thus, superhydrophobic textiles with the reduced total pore volume and smaller pore size would circumvent the adhesion. The findings of this study provide informative discussion on the characteristics of fibrous webs affecting the bacteria adhesion, which can be used as a fundamental design guide of anti-biofouling textiles.

Antibacterial Effect of Aluminum Surfaces Untreated and Treated with a Special Anodizing Based on Titanium Oxide Approved for Food Contact

One of the main concerns of the food industry is microbial adhesion to food contact surfaces and consequent contamination. We evaluated the potential bacteriostatic/bactericidal efficacy of aluminum surfaces with different large-scale roughness (0.25, 0.5 and 1 μm) before and after the surface treatment with a special anodizing based on titanium oxide nanotechnology (DURALTI®) and after 3 different sanitizing treatments, e.g., UV, alcohol and a natural product named Gold lotion. Four Gram-negative (Escherichia coli ATCC 25922, Salmonella typhimurium ATCC 1402, Yersinia enterocolitica ATCC 9610 and Pseudomonas aeruginosa ATCC 27588) and four Gram-positive (Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212, Bacillus cereus ATCC 14579 and Listeria monocytogenes NCTT 10888) bacteria were screened. As far as concerns aluminum surfaces without nanotechnology surface treatment, an overall bacteriostatic effect was observed for all strains with respect to the initial inoculum that was 106 CFU/mL. Conversely, an overall bactericidal effect was observed both for Gram-negative and -positive bacteria on DURALTI®-treated aluminum disks, regardless of roughness and sanitizing treatment. These results are innovative in terms of the great potential of the antibacterial activity of nanotechnologically treated food contact surfaces and their combination with some sanitizing agents that might be exploited in the food industry.

How microbes read the map: Effects of implant topography on bacterial adhesion and biofilm formation

Microbes have remarkable capabilities to attach to the surface of implanted medical devices and form biofilms that adversely impact device function and increase the risk of multidrug-resistant infections. The physicochemical properties of biomaterials have long been known to play an important role in biofilm formation. More recently, a series of discoveries in the natural world have stimulated great interest in the use of 3D surface topography to engineer antifouling materials that resist bacterial colonization. There is also increasing evidence that some medical device surface topographies, such as those designed for tissue integration, may unintentionally promote microbial attachment. Despite a number of reviews on surface topography and biofilm control, there is a missing link between how bacteria sense and respond to 3D surface topographies and the rational design of antifouling materials. Motivated by this gap, we present a review of how bacteria interact with surface topographies, and what can be learned from current laboratory studies of microbial adhesion and biofilm formation on specific topographic features and medical devices. We also address specific biocompatibility considerations and discuss how to improve the assessment of the anti-biofilm performance of topographic surfaces. We conclude that 3D surface topography, whether intended or unintended, is an important consideration in the rational design of safe medical devices. Future research on next-generation smart antifouling materials could benefit from a greater focus on translation to real-world applications.

Antibacterial Porous Electrospun Fibers as Skin Scaffolds for Wound Healing Applications

Electrospun fiber scaffolds have a huge potential for the successful treatment of infected wounds based on their unique properties. Although several studies report novel drug-loaded electrospun fiber-based biomaterials, many of these do not provide information on their interactions with eukaryotic and bacterial cells. The main aim of this study was to develop antibacterial drug-loaded porous biocompatible polycaprolactone (PCL) fiber scaffolds mimicking the native extracellular matrix for wound healing purposes. Mechanical property evaluation and different biorelevant tests were conducted in order to understand the structure-activity relationships and reveal how the surface porosity of fibers and the fiber diameter affect the scaffold interactions with the living bacterial and eukaryotic fibroblast cells. Cell migration and proliferation assays and antibiofilm assays enabled us to enlighten the biocompatibility and safety of fiber scaffolds and their suitability to be used as scaffolds for the treatment of infected wounds. Here, we report that porous PCL microfiber scaffolds obtained using electrospinning at high relative humidity served as the best surfaces for fibroblast attachment and growth compared to the nonporous microfiber or nonporous nanofiber PCL scaffolds. Porous chloramphenicol-loaded microfiber scaffolds were more elastic compared to nonporous scaffolds and had the highest antibiofilm activity. The results indicate that in addition to the fiber diameter and fiber scaffold porosity, the single-fiber surface porosity and its effect on drug release, mechanical properties, cell viability, and antibiofilm activity need to be understood when developing antibacterial biocompatible scaffolds for wound healing applications. We show that pores on single fibers within an electrospun scaffold, in addition to nano- and microscale diameter of the fibers, change the living cell-fiber interactions affecting the antibiofilm efficacy and biocompatibility of the scaffolds for the local treatment of wounds.

Bioadhesion in the oral cavity and approaches for biofilm management by surface modifications

BACKGROUND

All soft and solid surface structures in the oral cavity are covered by the acquired pellicle followed by bacterial colonization. This applies for natural structures as well as for restorative or prosthetic materials; the adherent bacterial biofilm is associated among others with the development of caries, periodontal diseases, peri-implantitis, or denture-associated stomatitis. Accordingly, there is a considerable demand for novel materials and coatings that limit and modulate bacterial attachment and/or propagation of microorganisms.

OBJECTIVES AND FINDINGS

The present paper depicts the current knowledge on the impact of different physicochemical surface characteristics on bioadsorption in the oral cavity. Furthermore, it was carved out which strategies were developed in dental research and general surface science to inhibit bacterial colonization and to delay biofilm formation by low-fouling or "easy-to-clean" surfaces. These include the modulation of physicochemical properties such as periodic topographies, roughness, surface free energy, or hardness. In recent years, a large emphasis was laid on micro- and nanostructured surfaces and on liquid repellent superhydrophic as well as superhydrophilic interfaces. Materials incorporating mobile or bound nanoparticles promoting bacteriostatic or bacteriotoxic properties were also used. Recently, chemically textured interfaces gained increasing interest and could represent promising solutions for innovative antibioadhesion interfaces. Due to the unique conditions in the oral cavity, mainly in vivo or in situ studies were considered in the review.

CONCLUSION

Despite many promising approaches for modulation of biofilm formation in the oral cavity, the ubiquitous phenomenon of bioadsorption and adhesion pellicle formation in the challenging oral milieu masks surface properties and therewith hampers low-fouling strategies.

CLINICAL RELEVANCE

Improved dental materials and surface coatings with easy-to-clean properties have the potential to improve oral health, but extensive and systematic research is required in this field to develop biocompatible and effective substances.

Inactivation of Listeria and E. coli by Deep-UV LED: effect of substrate conditions on inactivation kinetics

Irradiation with deep-ultraviolet light-emitting diodes (DUV LEDs) is emerging as a low energy, chemical-free approach to mitigate microbial contamination, but the effect of surface conditions on treatment effectiveness is not well understood. Here, inactivation of L. innocua and E. coli ATCC25922, as examples of Gram-positive and Gram-negative bacteria, respectively, by DUV LED of 280 nm wavelength was studied. Surface scenarios commonly encountered in environmental, clinical or food processing environments were used: nutrient rich surfaces, thin liquid films (TLF), and stainless steel surfaces (SS). DUV LED exposure achieved 5-log reduction for both strains within 10 min in most scenarios, except for TLF thicker than 0.6 mm. Inactivation kinetics in TLF and on dry SS followed the Weibull model (0.96 ≤ R2 ≤ 0.99), but the model overestimated inactivation by small-dose DUV on wet SS. Confocal microscopy revealed in situ that bacteria formed a dense outer layer at the liquid-air interface of the liquid droplet, protecting the cells inside the droplet from the bactericidal DUV. This resulted in lower than anticipated inactivation on wet SS at small DUV doses, and deviation from the Weibull model. These findings can be used to design effective DUV LED disinfection strategies for various surface conditions and applications.

Antibiofilm effect of mesoporous titania coatings on Pseudomonas aeruginosa biofilms

Activation of photocatalytic titania by ultraviolet-A (UVA) radiation has been proposed as a good approach for combating bacteria. Titania powder, in solution or immobilized on a surface, has excellent UVA-assisted killing properties on several microorganisms. However, these properties could not be demonstrated in biofilms of Pseudomonas aeruginosa, a resistant opportunistic human pathogen that can cause severe complications in patients who are immunocompromised or have burn wounds or cystic fibrosis. P. aeruginosa biofilms have detrimental effects on health and industry, causing serious economic damage. In this study, the effect of titania photocatalysis for controlling P. aeruginosa biofilms was investigated by employing different coatings obtained through sol-gel and evaporation-induced self-assembly. Biofilms were grown on non-mesoporous and mesoporous titania surfaces with different pore sizes, which were achieved based on the use of surfactants Brij-58 and Pluronics-F127. In addition, two structural forms of titania were assayed: amorphous and anatase. As well as inhibiting biofilm formation, these coatings significantly enhanced the bactericidal effect of UVA on P. aeruginosa biofilms. The most efficient surface with regard to total antibacterial effect was the mesoporous Brij-58-templated anatase film, which, compared to control biofilms, decreased the number of viable bacteria by about 5 orders, demonstrating the efficacy of this methodology as a disinfection system.

The Effects of Subcellular Nanograting Geometry on the Formation and Growth of Bacterial Biofilms

Biofilm formation by bacteria protects them against environmental stresses such as desiccation, shear forces and antimicrobial agents, making them much harder to remove and increasing their virulence and persistence in industrial water systems and biomedical equipment. One promising method of disrupting biofilm formation and growth is to employ passive surface structures to inhibit bacterial adhesion and aggregation. However, most studies thus far have mainly focused on the early stages of biofilm formation and it is unclear if the influence of surface topography in the early phase will propagate to later stages. Here, we attempt to address this with an investigation into the biofilm formation of Pseudomonas aeruginosa on 25 different nanograting geometries, with dimensions that were systematically varied from subcellular to cellular sizes. The biofilms were characterized from the exponential growth phase to the decline phase, in intervals of 24 H over 4 days, using confocal scanning laser microscopy. Comparing the maximum volume of biofilm formed on each surface over 96 H, it was found that approximately 1/3 of the nanograting geometries exhibited 72 ± 16 % lower biovolume density than a flat surface. Bacteria on these nanogratings were also observed to form 40 ± 11 % smaller microcolonies that were 17 ± 6 % less compact than that found on the control surface. The majority of these nanogratings had deep trenches (i.e. depth ≥ 70% of the cell diameter). Furthermore, P. aeruginosa cells were observed to multiply at approximately twice the rate on almost all the nanogratings compared to flat surfaces, but these cell populations also began to decline 24 H earlier than those on a flat surface. Using available literature on P. aeruginosa, a qualitative model was put forth, attributing the results to increased cell motility, decreased exopolysaccharide formation and disrupted psl adhesin/signal trails on nanogratings. These factors, together, led to the net effects of reduced attachment, increased scattering of cells and rapid decline of the biofilms on nanogratings. The insights derived from this study suggest that passive surface geometries can be designed and optimized to successfully control/inhibit biofilm formation and growth.

The influence of nanoporous anodic aluminum oxide on the initial adhesion of Streptococcus mitis and mutans

The use of nanoscale surface modifications offers a possibility to regulate the bacterial adherence behavior. The aim of this study was to evaluate the influence of nanoporous anodic aluminum oxide of different pore diameters on the bacterial species Streptococcus mitis and Streptococcus mutans. Nanoporous anodic aluminum oxide (AAO) surfaces with an average pore diameter of 15 and 40 nm, polished pure titanium and compact aluminum oxide (alumina) samples as reference material were investigated. S. mitis and mutans were evaluated for initial adhesion and viability after an incubation period of 30 and 120 min. After 30 min a significantly reduced growth of S. mitis and mutans on 15 nm samples compared to specimens with 40 nm pore diameter, alumina and titanium surfaces could be observed (p < .001). Even after 120 min incubation there was a significant difference between the surfaces with 15 nm pore diameter and the remaining samples (p < .001). AAO surfaces with a small pore diameter have an inhibitory effect on the initial adhesion of S. mitis and mutans. The use of such pore dimensions in the area of the implant shoulder represents a possibility to reduce the adhesion behavior of these bacterial species.

Micro- and Nanotopography Sensitive Bacterial Attachment Mechanisms: A Review

Bacterial attachment to material surfaces can lead to the development of biofilms that cause severe economic and health problems. The outcome of bacterial attachment is determined by a combination of bacterial sensing of material surfaces by the cell and the physicochemical factors in the near-surface environment. This paper offers a systematic review of the effects of surface topography on a range of antifouling mechanisms, with a focus on how topographical scale, from micro- to nanoscale, may influence bacterial sensing of and attachment to material surfaces. A good understanding of these mechanisms can facilitate the development of antifouling surfaces based on surface topography, with applications in various sectors of human life and activity including healthcare, food, and water treatment.

Biofilms in Food Processing Environments: Challenges and Opportunities

This review examines the impact of microbial communities colonizing food processing environments in the form of biofilms on food safety and food quality. The focus is both on biofilms formed by pathogenic and spoilage microorganisms and on those formed by harmless or beneficial microbes, which are of particular relevance in the processing of fermented foods. Information is presented on intraspecies variability in biofilm formation, interspecies relationships of cooperativism or competition within biofilms, the factors influencing biofilm ecology and architecture, and how these factors may influence removal. The effect on the biofilm formation ability of particular food components and different environmental conditions that commonly prevail during food processing is discussed. Available tools for the in situ monitoring and characterization of wild microbial biofilms in food processing facilities are explored. Finally, research on novel agents or strategies for the control of biofilm formation or removal is summarized.

Physico-chemistry from initial bacterial adhesion to surface-programmed biofilm growth

Biofilm formation is initiated by adhesion of individual bacteria to a surface. However, surface adhesion alone is not sufficient to form the complex community architecture of a biofilm. Surface-sensing creates bacterial awareness of their adhering state on the surface and is essential to initiate the phenotypic and genotypic changes that characterize the transition from initial bacterial adhesion to a biofilm. Physico-chemistry has been frequently applied to explain initial bacterial adhesion phenomena, including bacterial mass transport, role of substratum surface properties in initial adhesion and the transition from reversible to irreversible adhesion. However, also emergent biofilm properties, such as production of extracellular-polymeric-substances (EPS), can be surface-programmed. This review presents a four-step, comprehensive description of the role of physico-chemistry from initial bacterial adhesion to surface-programmed biofilm growth: (1) bacterial mass transport towards a surface, (2) reversible bacterial adhesion and (3) transition to irreversible adhesion and (4) cell wall deformation and associated emergent properties. Bacterial transport mostly occurs from sedimentation or convective-diffusion, while initial bacterial adhesion can be described by surface thermodynamic and Derjaguin-Landau-Verwey-Overbeek (DLVO)-analyses, considering bacteria as smooth, inert colloidal particles. DLVO-analyses however, require precise indication of the bacterial cell surface, which is impossible due to the presence of bacterial surface tethers, creating a multi-scale roughness that impedes proper definition of the interaction distance in DLVO-analyses. Application of surface thermodynamics is also difficult, because initial bacterial adhesion is only an equilibrium phenomenon for a short period of time, when bacteria are attached to a substratum surface through few surface tethers. Physico-chemical bond-strengthening occurs in several minutes leading to irreversible adhesion due to progressive removal of interfacial water, conformational changes in cell surface proteins, re-orientation of bacteria on a surface and the progressive involvement of more tethers in adhesion. After initial bond-strengthening, adhesion forces arising from a substratum surface cause nanoscopic deformation of the bacterial cell wall against the elasticity of the rigid peptidoglycan layer positioned in the cell wall and the intracellular pressure of the cytoplasm. Cell wall deformation not only increases the contact area with a substratum surface, presenting another physico-chemical bond-strengthening mechanism, but is also accompanied by membrane surface tension changes. Membrane-located sensor molecules subsequently react to control emergent phenotypic and genotypic properties in biofilms, most notably adhesion-associated ones like EPS production. Moreover, also bacterial efflux pump systems may be activated or mechano-sensitive channels may be opened upon adhesion-induced cell wall deformation. The physico-chemical properties of the substratum surface thus control the response of initially adhering bacteria and through excretion of autoinducer molecules extend the awareness of their adhering state to other biofilm inhabitants who subsequently respond with similar emergent properties. Herewith, physico-chemistry is not only involved in initial bacterial adhesion to surfaces but also in what we here propose to call "surface-programmed" biofilm growth. This conclusion is pivotal for the development of new strategies to control biofilm formation on substratum surfaces, that have hitherto been largely confined to the initial bacterial adhesion phenomena.

Eliminating the Need for Biocidal Agents in Anti-Biofouling Polymers by Applying Grafted Nanosilica Instead

A nondestructive one-step approach was applied for grafting biocide-free monodispersed silica nanoparticles (SNPs) with a diameter of 30 ± 10 nm on polystyrene, polyethylene, and polyvinyl chloride surfaces. The prepared surfaces were comprehensively characterized using spectroscopic (Fourier transform infrared attenuated total reflection, ultraviolet-visible, and X-ray photoelectron spectroscopy) and microscopic (high-resolution scanning electron microscopy and atomic force microscopy) methods. The modified polymers were found to maintain their original mechanical and physical properties, while their nanoroughness on the other hand had risen by 1.6-2.7 times because of SNP grafting. The SNP-grafted surfaces displayed anti-biofouling properties, resulting in a significant reduction in the attached Gram-positive Bacillus licheniformis or Gram-negative Pseudomonas aeruginosa bacteria compared to their nongrafted counterparts. Confocal laser scanning microscopy and scanning electron microscopy studies have confirmed that bacterial cells could not successfully adhere onto the SNP-grafted polymer films regardless of the polymer type, and their biofilm formation was therefore damaged. The presented facile and straightforward protocol allows eliminating the need for biocidal agents and resorts to grafted nanosilica instead. This strategy may serve as a feasible and safe platform for the development of sustainable anti-biofouling surfaces in biomedical devices; food, water, and air treatment systems; and industrial equipment.

The role of zeta potential in the adhesion of E. coli to suspended intertidal sediments

The extent of pathogen transport to and within aquatic systems depends heavily on whether the bacterial cells are freely suspended or in association with suspended particles. The surface charge of both bacterial cells and suspended particles affects cell-particle adhesion and subsequent transport and exposure pathways through settling and resuspension cycles. This study investigated the adhesion of Faecal Indicator Organisms (FIOs) to natural suspended intertidal sediments over the salinity gradient encountered at the transition zone from freshwater to marine environments. Phenotypic characteristics of three E. coli strains, and the zeta potential (surface charge) of the E. coli strains and 3 physically different types of intertidal sediments was measured over a salinity gradient from 0 to 5 Practical Salinity Units (PSU). A batch adhesion microcosm experiment was constructed with each combination of E. coli strain, intertidal sediment and 0, 2, 3.5 and 5 PSU. The zeta potential profile of one E. coli strain had a low negative charge and did not change in response to an increase in salinity, and the remaining E. coli strains and the sediments exhibited a more negative charge that decreased with an increase in salinity. Strain type was the most important factor in explaining cell-particle adhesion, however adhesion was also dependant on sediment type and salinity (2, 3.5 PSU > 0, 5 PSU). Contrary to traditional colloidal (Derjaguin, Landau, Vervey, and Overbeek (DLVO)) theory, zeta potential of strain or sediment did not correlate with cell-particle adhesion. E. coli strain characteristics were the defining factor in cell-particle adhesion, implying that diverse strain-specific transport and exposure pathways may exist. Further research applying these findings on a catchment scale is necessary to elucidate these pathways in order to improve accuracy of FIO fate and transport models.

Preparation and Antibiofilm Properties of Zinc Oxide/Porous Anodic Alumina Composite Films

The PAA (porous anodic alumina) films were prepared by two-step anodic oxidation after different times, and then the ZnO/PAA composite films were prepared by sol-gel method on their surface. Meanwhile, the ZnO/PAA composite films were characterized by X-ray diffraction (XRD), thermogravimetric/differential thermal analyzer (TG/DTA), Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and water contact angle (CA). The antibiofilm properties of ZnO/PAA composite films on Shewanella putrefaciens were measured simultaneously. The results show that the micromorphologies of PAA and ZnO/PAA composite films are affected by second anodization time. ZnO is a hexagonal wurtzite structure, and ZnO particles with a diameter of 10-30 nm attach to the inner or outer surfaces of PAA. After being modified by Si69, the ZnO films translate from hydrophilia to hydrophobicity. The ZnO/PAA film with the optimal antibiofilm properties is prepared on the PAA surface by two-step anodization for 40 min. The adherence of Shewanella putrefaciens is restrained by its super-hydrophobicity, and the growth of biofilm bacteria is inhibited by its abundant ZnO particles.

Bacterial Attachment, Aggregation, and Alignment on Subcellular Nanogratings

Recent investigations on the interactions of bacteria with micro/nanostructures have revealed a wide range of prokaryotic responses that were previously unknown. Despite these advances, however, it remains unclear how collective bacterial behavior on a surface would be influenced by the presence of anisotropic nanostructures with subcellular dimensions. To clarify this, the attachment, aggregation, and alignment of Pseudomonas aeruginosa on orderly subcellular nanogratings with systematically varied geometries were investigated. Compared with a flat surface, attachment and aggregation of bacteria on the nanogratings were reduced by up to 83 and 84% respectively, whereas alignment increased by a maximum of 850%. Using a semiempirical quantitative model, these results were shown to be caused by a lowering of physicochemical attraction between the substrate and bacteria, possible disruption to cell communication, and physical isolation of bacteria that were entrenched in the nanogratings by capillary action. Furthermore, the bacterial attachment level was generally found to be exponentially related to the contact area between the substrate and bacterial cells, except when there were significant deficits in the available contact area, which prompted the bacterial cells to employ their appendages to maintain a minimum attachment rate. Because the contact area for adhesion is strongly dependent on the geometry of the surface features and orientation of the bacterial cells, these results indicate that the conventional practice of using roughness parameters to draw quantitative relationships between surface topographies and bacterial attachment could suffer from inaccuracies due to the lack of shape and orientation information provided by these parameters. On the basis of these insights, design principles for generating maximal and minimal bacterial attachment on a surface were also proposed and verified with results reported in the literature.

Inhibition of Bacterial Adhesion on Nanotextured Stainless Steel 316L by Electrochemical Etching

Bacterial adhesion to stainless steel 316L (SS316L), which is an alloy typically used in many medical devices and food processing equipment, can cause serious infections along with substantial healthcare costs. This work demonstrates that nanotextured SS316L surfaces produced by electrochemical etching effectively inhibit bacterial adhesion of both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, but exhibit cytocompatibility and no toxicity toward mammalian cells in vitro. Additionally, the electrochemical surface modification on SS316L results in formation of superior passive layer at the surface, improving corrosion resistance. The nanotextured SS316L offers significant potential for medical applications based on the surface structure-induced reduction of bacterial adhesion without use of antibiotic or chemical modifications while providing cytocompatibility and corrosion resistance in physiological conditions.

Nanopatterning of steel by one-step anodization for anti-adhesion of bacteria

Surface nanopatterning of metals has been an effective technique for improved performance and functionalization. However, it is of great challenge to fabricate nanostructure on carbon steels despite their extensive use and urgent needs to maintain the performance reliability and durability. Here, we report a one-step anodization technique to nanopattern a carbon steel in 50 wt.% NaOH solution for highly effective anti-adhesion by sulphate reducing bacteria (SRB), i.e., Desulfovibrio desulfuricans subsp. desulfuricans (Beijerinck) Kluyver and van Niel. We characterize the morphology, structure, composition, and surface roughness of the nanostructured film formed on the steel as a function of anodizing potential. We quantify the surface hydrophobicity by contact angle measurements, and the SRB adhesion by fluorescent analysis. The optimal anodization potential of 2.0 V is determined for the best performance of anti-adhesion of SRB to the steel, resulting in a 23.5 times of reduction of SRB adhesion compared to bare steel. We discuss the mechanisms for the film formation on the steel during anodization, and the high-performance anti-adhesion of bacteria to nanopatterned steels. Our technique is simple, cost-effective and environment-friendly, providing a promising alternative for industry-scale surface nanopatterning of carbon steels for effective controlling of bacterial adhesion.

Antibiofilm effect of supramolecularly templated mesoporous silica coatings

Bacteria attached to solid surfaces and encased in a self-synthesized matrix, so-called biofilms, are highly difficult to eradicate and present negative impact on industry and human health. The ability of supramolecularly templated mesoporous silica coatings to inhibit biofilm formation in Pseudomonas aeruginosa is shown here. Assays employing submerged and air-liquid interface biofilms demonstrated that mesoporous coatings with tuned pore size significantly reduce the number of attached bacteria and matrix production. Given its versatility, scalability, robustness and low cost, our proposal is attractive for the production of transparent, inert and permanent antibiofilm coatings that could be applied on multiple surfaces.

Conjugation in Escherichia coli Biofilms on Poly(dimethylsiloxane) Surfaces with Microtopographic Patterns

Bacterial biofilms are highly tolerant to antimicrobials and play an important role in the development and spread of antibiotic resistance based on horizontal gene transfer due to close cell-to-cell contact. As an important surface property, topography has been shown to affect bacterial adhesion and biofilm formation. Here, we demonstrate that micrometer-scale surface topographies also affect horizontal gene transfer through conjugation in bacterial biofilms. Specifically, biofilm formation and associated conjugation on poly(dimethylsiloxane) (PDMS) surfaces with 10 μm tall protruding patterns were studied using fluorescently labeled donor and recipient strains of Escherichia coli. The results demonstrate that square-shaped topographic patterns with side length of 20, 50, and 100 μm and interpattern distance equal to or larger than 10 μm promote biofilm formation and conjugation compared to the smooth control. The vertical sides of these topographic features were found to be the "hot spots" for bacterial conjugation compared to the top of patterns and grooves between topographic features. The increase in conjugation frequency on the sides of topographic patterns was attributed to the high cell density of recipient cells at these locations. A motility (motB) mutant of the recipient strain exhibited defects in biofilm formation at the "hot spots" and conjugation, which were recovered by complementing the motB gene on a plasmid. These results also provided guidance for designing surface topographies that can reduce conjugation. Specifically, 10 μm tall hexagon-shaped topographic patterns with side length of 15 μm and interpattern distance of 2 μm were prepared to reduce biofilm formation on the side of protruding patterns and interrupt cell-cell interaction in the grooves. This topography exhibited 85% and 46% reduction of biofilm formation and associated conjugation, respectively, compared to the smooth control.