Influence of surface sub-micropattern on the adhesion of pioneer bacteria on metals

Development of Robust Chitosan–Silica Class II Hybrid Coatings with Antimicrobial Properties for Titanium Implants

The purpose of this study was to develop robust class II organic–inorganic films as antibacterial coatings on titanium alloy (Ti6Al4V) implants. Coating materials were prepared from organic chitosan (20–80 wt.%) coupled by 3-glycydoxytrimethoxysilane (GPTMS) with inorganic tetraethoxysilane (TEOS). These hybrid networks were imbedded with antimicrobial silver nanoparticles (AgNPs) and coated onto polished and acid-etched Ti6Al4V substrates. Magic-angle spinning nuclear magnetic resonance (13CMAS-NMR), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and the ninhydrin assay, confirmed the presence and degree of covalent crosslinking (91%) between chitosan and GPTMS. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) identified surface roughness and microtopography on thin films and confirmed homogeneous distribution of elements throughout the coating. Cross-hatch and tensile adhesion testing demonstrated the robustness and adherence (15–20 MPa) of hybrid coatings to acid-etched titanium substrates. Staphylococcus aureus and Escherichia coli cultures and their biofilm formation were inhibited by all hybrid coatings. Antibacterial effects increased markedly for coatings loaded with AgNPs and appeared to increase with chitosan content in biofilm assays. These results are promising in the development of class II hybrid materials as robust and highly adherent antibacterial films on Ti6Al4V implants.

Contact infection of infectious disease onboard a cruise ship

Cruise tourism has become more popular. Long-term personal contact, complex population flows, a lack of medical care facilities, and defective infrastructure aboard most cruise ships is likely to result in the ship becoming an incubator for infectious diseases. In this paper, we use a cruise ship as a research scenario. Taking into consideration personal behavior, the nature and transfer route of the virus across different surfaces, virus reproduction, and disinfection, we studied contact infection of infectious disease on a cruise ship. Using gastroenteritis caused by the norovirus as an example, we analyzed the characteristics of infectious disease propagation based on simulation results under different conditions. We found hand washing are the most important factors affecting virus propagation and passenger infection. It also decides either the total number of virus microorganisms or the virus distribution in different functional areas. The transfer rate between different surfaces is a key factor influencing the concentricity of the virus. A high transfer rate leads to high concentricity. In addition, the risk of getting infected is effectively reduced when the disinfection frequency is above a certain threshold. The efficiency of disinfection of functional areas is determined by total virus number and total contact times of surfaces.

The impact of structure dimensions on initial bacterial adhesion

Substrate topography can have profound effects on initial bacterial adhesion during biofilm formation. We applied Staphylococcus epidermidis and Escherichia coli cells onto periodically structured substrates with different structure dimensions, structure types and wetting properties. We found a strong dependence of cell retention on the structure dimensions of the applied substrates. Periodicities in the range of the cell size increased, whereas smaller periodicities decreased cell retention, independent of contact time (minutes to hours) and hydrophobicity. These novel insights on the role of surface topography on bacterial retention might facilitate the development of non-fouling surfaces in the future.

The importance of 2D aggregates on the antimicrobial resistance of Staphylococcus aureus sessile bacteria

Biofilms formed on implanted devices are difficult to eradicate. Adhesion mechanism, high bacterial density, aggregation, induction of persisters and stressed bacteria are some of the factors considered when the antimicrobial resistance of these biofilms is analyzed. The aim of this work was to provide an alternative approach to the understanding of this issue by using a specially designed experimental set up that includes the use of microstructured (MS) surfaces (potential inhibitors of bacterial aggregation) in combination with antimicrobial agents (streptomycin and levofloxacin) against Staphylococcusaureus attached cells. Biofilms formed on smooth surfaces were used as plain controls (biofilmed-PC) characterized by the formation of dense 2D bacterial aggregates. Results showed bacterial persistence when streptomycin or levofloxacin were applied to PC-biofilms. The antimicrobial activity of both antibiotics was enhanced when bacteria were attached on MS, where single cells or small aggregates were observed. Thus, dense 2D aggregates of bacteria seem to be crucial as a required previous stage to develop the antimicrobial resistance.

Novel materials for biofilm reactors and their characterization

The application of adherently growing microorganisms for biotechnological production processes is established, but it is still a niche technology with only a small economic impact. However, novel approaches are under development for new types of biofilm reactors. In this context, increasingly more microstructured metal surfaces are being investigated, and they show positive effects on the bacterial growth and the biofilm establishment. However, for comparison of the data, the different surface materials have to correspond in their different characteristics, such as wettability and chemical composition. Also, new materials, such as plastic composite supports, were developed. To understand the interaction between these new materials and the biofilm-producing microorganisms, different surface science methods have to be applied to reveal a detailed knowledge of the surface characteristics. In conclusion, microstructured surfaces show a high potential for enhanced biofilm growth, probably accompanied by an enhanced productivity of the microorganisms.

Interactions in bacterial biofilm development: a structural perspective

A community-based life style is the normal mode of growth and survival for many bacterial species. These cellular accretions or biofilms are initiated upon recognition of solid phases by cell surface exposed adhesive moieties. Further cell-cell interactions, cell signalling and bacterial replication leads to the establishment of dense populations encapsulated in a mainly self-produced extracellular matrix; this comprises a complex mixture of macromolecules. These fascinating architectures protect the inhabitants from radiation damage, dehydration, pH fluctuations and antimicrobial compounds. As such they can cause bacterial persistence in disease and problems in industrial applications. In this review we discuss the current understandings of these initial biofilm-forming processes based on structural data. We also briefly describe latter biofilm maturation and dispersal events, which although lack high-resolution insights, are the present focus for many structural biologists working in this field. Finally we give an overview of modern techniques aimed at preventing and disrupting problem biofilms.

Modification of the surfaces of medical devices to prevent microbial adhesion and biofilm formation

BACKGROUND

The development of devices with surfaces that have an effect against microbial adhesion or viability is a promising approach to the prevention of device-related infections.

AIM

To review the strategies used to design devices with surfaces able to limit microbial adhesion and/or growth.

METHODS

A PubMed search of the published literature.

FINDINGS

One strategy is to design medical devices with a biocidal agent. Biocides can be incorporated into the materials or coated or covalently bonded, resulting either in release of the biocide or in contact killing without release of the biocide. The use of biocides in medical devices is debated because of the risk of bacterial resistance and potential toxicity. Another strategy is to modify the chemical or physical surface properties of the materials to prevent microbial adhesion, a complex phenomenon that also depends directly on microbial biological structure and the environment. Anti-adhesive chemical surface modifications mostly target the hydrophobicity features of the materials. Topographical modifications are focused on roughness and nanostructures, whose size and spatial organization are controlled. The most effective physical parameters to reduce bacterial adhesion remain to be determined and could depend on shape and other bacterial characteristics.

CONCLUSIONS

A prevention strategy based on reducing microbial attachment rather than on releasing a biocide is promising. Evidence of the clinical efficacy of these surface-modified devices is lacking. Additional studies are needed to determine which physical features have the greatest potential for reducing adhesion and to assess the usefulness of antimicrobial coatings other than antibiotics.

Citrate-capped silver nanoparticles showing good bactericidal effect against both planktonic and sessile bacteria and a low cytotoxicity to osteoblastic cells

A common problem with implants is that bacteria can form biofilms on their surfaces, which can lead to infection and, eventually, to implant rejection. An interesting strategy to inhibit bacterial colonization is the immobilization of silver (Ag) species on the surface of the devices. The aim of this paper is to investigate the action of citrate-capped silver nanoparticles (AgNPs) on clinically relevant Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria in two different situations: (i) dispersed AgNPs (to assess the effect of AgNPs against planktonic bacteria) and (ii) adsorbed AgNPs on titanium (Ti) substrates, a material widely used for implants (to test their effect against sessile bacteria). In both cases, the number of surviving cells was quantified. The small amount of Ag on the surface of Ti has an antimicrobial effect similar to that of pure Ag surfaces. We have also investigated the capability of AgNPs to kill planktonic bacteria and their cytotoxic effect on UMR-106 osteoblastic cells. The minimum bactericidal concentration found for both strains is much lower than the AgNP concentration that leads to cytotoxicity to osteoblasts. Planktonic P. aeruginosa show a higher susceptibility to Ag than S. aureus, which can be caused by the different wall structures, while for sessile bacteria, similar results are obtained for both strains. This can be explained by the presence of extracellular polymeric substances in the early stages of P. aeruginosa biofilm formation. Our findings can be important to improving the performance of Ti-based implants because a good bactericidal action is obtained with very small quantities of Ag, which are not detrimental to the cells involved in the osseointegration process.