Bioadhesion on Textured Interfaces in the Human Oral Cavity—An In Situ Study

Extensive biofilm formation on materials used in restorative dentistry is a common reason for their failure and the development of oral diseases like peri-implantitis or secondary caries. Therefore, novel materials and strategies that result in reduced biofouling capacities are urgently sought. Previous research suggests that surface structures in the range of bacterial cell sizes seem to be a promising approach to modulate bacterial adhesion and biofilm formation. Here we investigated bioadhesion within the oral cavity on a low surface energy material (perfluorpolyether) with different texture types (line-, hole-, pillar-like), feature sizes in a range from 0.7–4.5 µm and graded distances (0.7–130.5 µm). As a model system, the materials were fixed on splints and exposed to the oral cavity. We analyzed the enzymatic activity of amylase and lysozyme, pellicle formation, and bacterial colonization after 8 h intraoral exposure. In opposite to in vitro experiments, these in situ experiments revealed no clear signs of altered bacterial surface colonization regarding structure dimensions and texture types compared to unstructured substrates or natural enamel. In part, there seemed to be a decreasing trend of adherent cells with increasing periodicities and structure sizes, but this pattern was weak and irregular. Pellicle formation took place on all substrates in an unaltered manner. However, pellicle formation was most pronounced within recessed areas thereby partially masking the three-dimensional character of the surfaces. As the natural pellicle layer is obviously the most dominant prerequisite for bacterial adhesion, colonization in the oral environment cannot be easily controlled by structural means.     

Enzymes for Antifouling Strategies

During the past decades, much effort has been made to find efficient alternative solutions to prevent and/or disrupt the adhesion of fouling organisms to surfaces. The use of enzymes emerges among the investigated approaches as one of the favorite candidate antifouling technologies due to enzymes' biodegradability and affordable prices. An overview of the different enzymatic antifouling strategies is presented, highlighting the most promising groups of enzymes, and their utilization upon surface-confinement to control biofouling. While the main strategies to control marine biofouling include the degradation of secreted adhesives and the production of antifouling compounds, the main concepts to control pathogenic biofilms are based on cell lysis and on the degradation of extracellular matrix polymers. Although immobilization can improve enzyme stability, activity and antifouling performance, up to date relatively few scientific articles concerning the use of immobilized enzymes to control biofouling have been published. The successful incorporation of enzymes into coatings yielding surfaces with broad antifouling spectrum and long-term efficacy remains a challenge.     

Assessing the Antimicrobial Activity of Polyisoprene Based Surfaces

There has been an intense research effort in the last decades in the field of biofouling prevention as it concerns many aspects of everyday life and causes problems to devices, the environment, and human health. Many different antifouling and antimicrobial materials have been developed to struggle against bacteria and other micro- and macro-organism attachment to different surfaces. However the “miracle solution” has still to be found. The research presented here concerns the synthesis of bio-based polymeric materials and the biological tests that showed their antifouling and, at the same time, antibacterial activity. The raw material used for the coating synthesis was natural rubber. The polyisoprene chains were fragmented to obtain oligomers, which had reactive chemical groups at their chain ends, therefore they could be modified to insert polymerizable and biocidal groups. Films were obtained by radical photopolymerization of the natural rubber derived oligomers and their structure was altered, in order to understand the mechanism of attachment inhibition and to increase the efficiency of the anti-biofouling action. The adhesion of three species of pathogenic bacteria and six strains of marine bacteria was studied. The coatings were able to inhibit bacterial attachment by contact, as it was verified that no detectable leaching of toxic molecules occurred.     

Investigation of bacterial attachment and biofilm formation of two different Pseudoalteromonas species: Comparison of different methods

Biological fouling in marine environments creates numerous problems for engineered structures. Microbial attachment to a solid surface and biofilm formation initiates the process of biofouling. Therefore, detecting the initial bacterial attachment and understanding the mechanism of biofilm formation are important for controlling biofouling. In the present study, the mechanisms of bacterial attachment and biofilm formation of two marine isolated bacteria, namely Pseudoalteromonas sp. and Pseudoalteromonas flavipulchra on Ti-coated samples were examined through different electrochemical, surface analysis and thermodynamic methods. The results revealed that the rate of bacterial attachment and mechanism of biofilm formation varied for different species of bacteria. The amount of exopolysaccharide production could affect the bacterial attachment rate. Open circuit potentiometry has been found to be a valid and simple technique for continuous real-time monitoring of the biofilm formation compared to other electrochemical and thermodynamic techniques. Finally, two different models have been suggested to explain initial adhesion and biofilm formation of bacteria of different species.     

Materials and surface engineering to control bacterial adhesion and biofilm formation: A review of recent advances

Bacterial adhesion to surfaces and subsequent biofilm formation are a leading cause of chronic infections and biofouling. These processes are highly sensitive to environmental factors and present a challenge to research using traditional approaches with uncontrolled surfaces. Recent advances in materials research and surface engineering have brought exciting opportunities to pattern bacterial cell clusters and to obtain synthetic biofilms with well-controlled cell density and morphology of cell clusters. In this article, we will review the recent achievements in this field and comment on the future directions.     

Polymer brush coatings for combating marine biofouling

A variety of functional polymer brushes and coatings have been developed for combating marine biofouling and biocorrosion with much less environmental impact than traditional biocides. This review summarizes recent developments in marine antifouling polymer brushes and coatings that are tethered to material surfaces and do not actively release biocides. Polymer brush coatings have been designed to inhibit molecular fouling, microfouling and macrofouling through incorporation or inclusion of multiple functionalities. Hydrophilic polymers, such as poly(ethylene glycol), hydrogels, zwitterionic polymers and polysaccharides, resist attachment of marine organisms effectively due to extensive hydration. Fouling release polymer coatings, based on fluoropolymers and poly(dimethylsiloxane) elastomers, minimize adhesion between marine organisms and material surfaces, leading to easy removal of biofoulants. Polycationic coatings are effective in reducing marine biofouling partly because of their good bactericidal properties. Recent advances in controlled radical polymerization and click chemistry have also allowed better molecular design and engineering of multifunctional brush coatings for improved antifouling efficacies.     

Application of marine biotechnology in the production of natural biocides for testing on environmentally innocuous antifouling coatings

The widely recognized biofouling phenomenon has many negative consequences for artificial structures that are in contact with seawater in the form of structural defects and additional expenses for maritime companies due to cleaning and prevention processes. After having analyzed the serious environmental problems caused by an indiscriminate use of highly toxic biocides coming from organic derivatives of tin compounds and the uncontrolled emissions of volatile organic compounds (VOC) to the atmosphere, the evolving technology of antifouling paintings (further mandated by current environmental standards) aims to develop environmentally innocuous water-based coverings in which extracts of the very same marine world are used as biocide compounds. Water-based coatings are being developed that use low-toxic elements and natural biocides, where bacteria is isolated from surfaces immersed in the marine environment, creating a promising source of natural antifouling compounds. The result is a new environmentally friendly antifouling coating that is able to mitigate the problem of biofouling without affecting the surrounding medium, and which may be applied on any artificial structure in contact with seawater. An erratum to this article can be found at     

Anti-Biofilm Performance of Three Natural Products against Initial Bacterial Attachment

Marine bacteria contribute significantly towards the fouling consortium, both directly (modern foul release coatings fail to prevent “slime” attachment) and indirectly (biofilms often excrete chemical cues that attract macrofouling settlement). This study assessed the natural product anti-biofilm performance of an extract of the seaweed, Chondrus crispus, and two isolated compounds from terrestrial sources, (+)-usnic acid and juglone, against two marine biofilm forming bacteria, Cobetia marina and Marinobacter hydrocarbonoclasticus. Bioassays were developed using quantitative imaging and fluorescent labelling to test the natural products over a range of concentrations against initial bacterial attachment. All natural products affected bacterial attachment; however, juglone demonstrated the best anti-biofilm performance against both bacterial species at a concentration range between 5–20 ppm. In addition, for the first time, a dose-dependent inhibition (hormetic) response was observed for natural products against marine biofilm forming bacteria.     

Biofilms: The Stronghold of Legionella pneumophila

Legionellosis is mostly caused by Legionella pneumophila and is defined as a severe respiratory illness with a case fatality rate ranging from 5% to 80%. L. pneumophila is ubiquitous in natural and anthropogenic water systems. L. pneumophila is transmitted by inhalation of contaminated aerosols produced by a variety of devices. While L. pneumophila replicates within environmental protozoa, colonization and persistence in its natural environment are also mediated by biofilm formation and colonization within multispecies microbial communities. There is now evidence that some legionellosis outbreaks are correlated with the presence of biofilms. Thus, preventing biofilm formation appears as one of the strategies to reduce water system contamination. However, we lack information about the chemical and biophysical conditions, as well as the molecular mechanisms that allow the production of biofilms by L. pneumophila. Here, we discuss the molecular basis of biofilm formation by L. pneumophila and the roles of other microbial species in L. pneumophila biofilm colonization. In addition, we discuss the protective roles of biofilms against current L. pneumophila sanitation strategies along with the initial data available on the regulation of L. pneumophila biofilm formation.     

Bio-Interactive Zwitterionic Dental Biomaterials for Improving Biofilm Resistance: Characteristics and Applications

Biofilms are formed on surfaces inside the oral cavity covered by the acquired pellicle and develop into a complex, dynamic, microbial environment. Oral biofilm is a causative factor of dental and periodontal diseases. Accordingly, novel materials that can resist biofilm formation have attracted significant attention. Zwitterionic polymers (ZPs) have unique features that resist protein adhesion and prevent biofilm formation while maintaining biocompatibility. Recent literature has reflected a rapid increase in the application of ZPs as coatings and additives with promising outcomes. In this review, we briefly introduce ZPs and their mechanism of antifouling action, properties of human oral biofilms, and present trends in anti-biofouling, zwitterionic, dental materials. Furthermore, we highlight the existing challenges in the standardization of biofilm research and the future of antifouling, zwitterated, dental materials.     

Antifouling ability of polyethylene glycol of different molecular weights grafted onto polyester surfaces by cold plasma

Different molecular weights of polyethylene glycol (PEG, MW 200, 400, 600, 2000, and 4600) were grafted onto silicon tetrachloride (SiCl₄) plasma functionalized polyethylene terephthalate (PET) surfaces. Dramatic increase of the C–O peak in the C1s high-resolution spectra determined by electron spectroscopy for chemical analysis suggests that PEG was successfully grafted. PEG-grafted PET showed significant inhibition of attachment and biofilm formation by Salmonella enterica sv. Typhimurium compared to unmodified PET. The antifouling ability of PEG-grafted PET surfaces was affected by the molecular weight of PEG and PEG2000 was the most effective. Both PEG600- and PEG2000-grafted PET also significantly inhibited biofilm formation by Listeria monocytogenes. Stability tests showed that over 2-month storage under ambient conditions PEG2000-grafted PET demonstrated reduced antifouling ability, but still significantly reduced biofilm formation by S. enterica sv. Typhimurium.     

Biofouling reduction of EPDM by radiation-assisted modification for water environment applications

Ethylene propylene diene elastomer (EPDM) harbors diverse microbiota that form biofilms. Such biofilms may contaminate water and can increase drag force impacting the hydrodynamic performance of a ship, once it is used as fenders. Here, the EPDM surface is modified by radiation-assisted grafting to prevent biofilm formation. Three different monomers, namely, methacrylic acid (MAA), isodecyl methacrylate (IDM), and lauryl methacrylate (LMA), are grafted on EPDM. The modified surfaces are characterized by Fourier transform infrared (FTIR) spectroscopy, surface wettability, mechanical and dynamic mechanical properties (DMA), and scanning electron microscopy (SEM). The modified surfaces are subjected to biofouling by prominent biofilm adherents, that is, Pseudomonas aeruginosa and Klebsiella pneumoniae. The standard plate count and resazurin fluorescence assays are performed to observe the microbial load on these surfaces. The MAA-grafted EPDM, which is hydrophilic in nature, shows a considerable decrease in bacterial adhesion compared to pure EPDM, but for IDM and LMA-grafted EPDM, it is the opposite. The deterioration of the surface with bacteria by environmental scanning electron microscopy (ESEM) supports the findings. The tensile property of the modified EPDM is observed to be within satisfactory limits. After such modification, the EPDM is expected to expand its application.     

Clickable Zwitterionic Copolymer as a Universal Biofilm‐Resistant Coating

Hospital‐acquired infections are often caused by bacterial biofilms on medical devices. To prevent biofilm formation, herein, a universal coating of an antifouling polymer that inhibits the initial adhesion of bacteria is developed. This copolymer is made of methacryloyloxyethyl phosphorylcholine (MPC) and a methacrylate‐substituted dihydrolipoic acid (DHLA) (poly(MPC‐DHLA)). The MPC units provide the antifouling property, while the DHLA units offer cross‐linkable sites via thiol‐ene reactions to form the stable coated copolymer film. Without the requirement for covalent surface grafting, the poly(MPC‐DHLA) coating on various biomedically relevant substrates is investigated, where X‐ray photoelectron spectroscopy, water contact angle measurements, atomic force microscopy, and ellipsometry are used to confirm the success of the surface coating. Moreover, to mimic an actual clinical use, the copolymer coating is applied on a titanium dental substrate and the ability to inhibit biofilm formation by Staphylococcus aureus is quantified and visualized by crystal violet staining and scanning electron microscopy, respectively. As compared with the bare substrate, an effective reduction in bacterial adhesion and suppression of the subsequent biofilm formation is observed on the copolymer‐modified substrate. These features are maintained for up to 7 d indicating the durability as well as universal applicability of this coating approach.     

Cupric tannate: A low copper content antifouling pigment

Fouling organisms attached to man-made surfaces submerged in seawater constitute a major worldwide technical and economical problem. Protection against biofouling is essential for efficient service of boats and ships. Due to recent and imminent restrictions of the use of traditional toxic antifouling paints, there is a growing need for new alternative compounds that ensure a good performance without polluting the marine ecosystem.

The aim of this work is to develop a new antifouling formulation using compounds of natural origin, i.e. tannates, in combination with a minimum concentration of a known bioactive pigment, i.e. copper.

Laboratory assays have shown that cupric tannate has a narcotic effect on biofouling larvae. In the field, after 12 months of immersion in Mar del Plata harbor (Argentine), none of the tested painted panels showed macrofouling organisms. This result was obtained with a large decrease in copper content in the order of 40 times relative to conventional cuprous oxide based paints.

Because copper tannate is not lethal at low concentrations, this pigment has an excellent potential as an antifouling agent.     

Mechanisms of biofilm formation on aluminium tubes

The development of biofilms in contact with flowing liquids was monitored in a biofouling culture apparatus which contained aluminium tubes and which was inoculated with Pseudomonas fluorescens. Tests were carried out in which, alternately, the nutrient feed or the bacterial supply was stopped. Results showed that once the surface is colonised, the predominant mechanism for biofilm development was growth within the film. Maximum biofilm development occurred at liquid flow velocities around 1 m s^?1. Rapid development occurred even in the presence of very small amounts of nutrient.     

Chitosan Nanocomposite Coatings Containing Chemically Resistant ZnO–SnOx Core–shell Nanoparticles for Photocatalytic Antifouling

Functional nanocomposites with biopolymers and zinc oxide (ZnO) nanoparticles is an emerging application of photocatalysis in antifouling coatings. The reduced chemical stability of ZnO in the acidic media in which chitosan is soluble affects the performance of chitosan nanocomposites in antifouling applications. In this study, a thin shell of amorphous tin dioxide (SnO_x) was grown on the surface of ZnO to form ZnO–SnO_x core–shell nanoparticles that improved the chemical stability of the photocatalyst nanoparticles, as examined at pH 3 and 6. The photocatalytic activity of ZnO–SnO_x in the degradation of methylene blue (MB) dye under visible light showed a higher efficiency than that of ZnO nanoparticles due to the passivation of electronic defects. Chitosan-based antifouling coatings with varying percentages of ZnO or ZnO–SnO_x nanoparticles, with or without the glutaraldehyde (GA) crosslinking of chitosan, were developed and studied. The incorporation of photocatalysts into the chitosan matrix enhanced the thermal stability of the coatings. Through a mesocosm study using running natural seawater, it was found that chitosan/ZnO–SnO_x/GA coatings enabled better inhibition of bacterial growth compared to chitosan coatings alone. This study demonstrates the antifouling potential of chitosan nanocomposite coatings containing core–shell nanoparticles as an effective solution for the prevention of biofouling.     

Effects of marine microbial biofilms on the biocide release rate from antifouling paints—A model-based analysis

The antifouling (AF) paint model of Kiil et al. [S. Kiil, C.E. Weinell, M.S. Pedersen, K. Dam-Johansen, Analysis of self-polishing antifouling paints using rotary experiments and mathematical modelling, Ind. Eng. Chem. Res. 40 (2001) 3906–3920] and the simplified biofilm growth model of Gujer and Wanner [W. Gujer, O. Wanner, Modeling mixed population biofilms, in: W.G. Characklis, K.C. Marshall (Eds.), Biofilms, Wiley–Interscience, New York, 1990] are used to provide a reaction engineering-based insight to the effects of marine microbial slimes on biocide leaching and, to a minor extent, polishing behaviour of AF paints. It is concluded that the perturbation of the local sea water conditions (e.g. pH), as a consequence of the metabolic activity of the biofilm should not affect the net biocide leaching and binder reaction rates significantly. This results from the thin and poorly active biofilms which presumably grow onto the highly effective modern AF paints. According to simulations, the experimental decrease in the biocide leaching rate caused by biofilm growth must be mainly attributed to adsorption of the biocide by the exopolymeric substances secreted by the microorganisms. The effects of biofilms on the leaching of any generic active compound (e.g. natural antifoulants) are discussed in relation to their potential release mechanisms. The largest influence of biofilms is predicted for those active compounds that are released by a diffusion-controlled mechanism (typically tin-free algaecides).     

Techniques for the measurement of natural product incorporation into an antifouling coating

The control of biofouling can be achieved by a variety of methods but for an open system, such as a ship's hull, a protective paint coating is the most adopted method. The incorporation of a natural product extract directly into a coating has received little previous attention. This study has investigated a combination of the antifouling compound (a natural product extract) and the delivery system (control depletion polymer) investigated together. It was necessary to investigate the natural product incorporation into a coating and finally assess the antifouling system including the primer layers in the natural marine environment. Natural products must first be practical as antifoulants to be developed further into a functional system by their incorporation into surfaces or coatings. To demonstrate this, the natural product under investigation was homogenised into a blank proprietary antifouling paint system binder, applied to primed and un-primed ship grade steel and immersed in marine environments. Electrochemical techniques were used to investigate the effects of natural product incorporation into a coating. In addition, optical and scanning electron microscopes were used to assess the physical characteristics of the coating system. The most rigorous test for an antifouling system is a field trial. Field trials were completed at a raft exposure facility, in estuarine dock conditions at the Empress dock, National Oceanography Centre, Southampton, UK.     

Biofilm Matrix and Its Regulation in Pseudomonas aeruginosa

Biofilms are communities of microorganisms embedded in extracellular polymeric substances (EPS) matrix. Bacteria in biofilms demonstrate distinct features from their free-living planktonic counterparts, such as different physiology and high resistance to immune system and antibiotics that render biofilm a source of chronic and persistent infections. A deeper understanding of biofilms will ultimately provide insights into the development of alternative treatment for biofilm infections. The opportunistic pathogen Pseudomonas aeruginosa, a model bacterium for biofilm research, is notorious for its ability to cause chronic infections by its high level of drug resistance involving the formation of biofilms. In this review, we summarize recent advances in biofilm formation, focusing on the biofilm matrix and its regulation in P. aeruginosa, aiming to provide resources for the understanding and control of bacterial biofilms.     

Kinetics of Adhesion Staphylococcus aureus on Glass in the Presence of Sodium Lauryl Sulfate

Bacterial contamination of surfaces is a natural and spontaneous process that often results in the formation of biofilms. The extracellular matrix of biofilm is mostly composed of proteins, polysaccharides, and extracellular DNA and is responsible for the strong persistent ability of biofilm in the food industry. Despite cleaning and disinfection processes, persistent bacteria cause a major problem in food processing environments. Synthetic surfactants, mainly anionic surface-active agent, are commonly used as detergents, foaming agents, wetting agents, emulsifiers, and dispersants. Their tendency to adsorb to surfaces and interfaces and modify their surface tension, is considered among their main properties. They also have the ability to attach to bioactive macromolecules such as proteins, peptides, and DNA causing cell membrane damage. In order to estimate the adhesion kinetic and proliferation of pathogenic bacteria Staphylococcus aureus, the surface of glass was coated with anionic surfactant Sodium Lauryl Sulfate (SLS). Moreover, SLS was added in suspension with the culture medium. The physicochemical properties of the material were calculated using the contact angle measurement method and bacterial hydrophobicity using the microbial adhesion to hydrocarbons (MATH) test. The obtained results showed that the number of adhering cells increased gradually as a function of time. However, changing the surface properties of the glass and S. aureus has affected the rate of adherent cells with time as well as their organization. SLS inhibited the attachment of cells, whether it is added with the microbial suspension or at the surface of the support. Generally, the present article points to a relationship between the microbial adhesion, the surface chemistry of the solid material and the bacteria, and the suspension properties.