Nanoscale investigation of pathogenic microbial adhesion to a biomaterial

The effect of photodynamic therapy using Radachlorin on biofilm-forming multidrug-resistant bacteria

OBJECTIVES

This study aimed to test the effect of photodynamic therapy (PDT) on the inhibition and removal of biofilms containing multidrug-resistant Acinetobacter baumannii.

METHODS

Using multidrug-resistant A. baumannii strains, an antibiotic susceptibility test was performed using the Gram-negative identification card of the Vitek 2 system (bioMérieux Inc., France), as well as an analysis of resistance genes, the effects of treatment with a light-emitting diode (LED) array using Radachlorin (RADA-PHARMA Co., Ltd., Russia), and transmission and scanning electron microscopy to confirm the biofilm-inhibitory effect of PDT.

RESULTS

The antibiotic susceptibility test revealed multiple resistance to the antibiotics imipenem and meropenem in the carbapenem class. A class-D-type β-lactamase was found, and OXA-23 and OXA-51 were found in 100% of 15 A. baumannii strains. After PDT using Radachlorin, morphological observations revealed an abnormal structure due to the loss of the cell membrane and extensive morphological changes, including low intracellular visibility and small vacuoles attached to the cell membrane.

CONCLUSION

PDT involving a combination of LED and Radachlorin significantly eliminated the biofilm of multidrug-resistant A. baumannii. Observations made using electron microscopy showed that PDT combining LED and Radachlorin was effective. Additional studies on the effective elimination of biofilms containing multidrug-resistant bacteria are necessary, and we hope that a treatment method superior to sterilization with antibiotics will be developed in the future.

Quantitative determination of rapid biomass formation on pyro-electrified polymer sheets

The ability of a bacterial strain to form a biofilm is strictly related to its pathogenicity. Bacterial adherence and early biofilm formation are influenced by chemical, physical and biological factors that determine their pathogenic properties. We recently presented in literature the ability of pyro-electrified polymer sheets to promote rapid biofilm formation, based on what we called biofilm electrostatic test (BET) carriers. Here we performed a step forward by presenting a comprehensive characterization of the BET methodology through a quantitative evaluation of the biomass on the BET-carrier in the very early stages of incubation. Two bacterial suspensions of Escherichia coli were added to the surface of the BET-carrier, with one order of magnitude difference in initial optical density. The biofilms were stained at different incubation times, while the crystal violet assay and the live/dead reaction kit were used for evaluating the biomass and the viability, respectively. The BET-carrier systematically promoted a faster biofilm formation even in case of very diluted bacterial concentration. The results suggest that the BET-carrier could be used for evaluating rapidly the ability of bacteria to form biofilms and thus their inclination to pathogenicity, thanks to the challenging acceleration in biofilm formation.

Atomic Force Microscopy Investigation of the Contributions of Listeria monocytogenes Cell-Wall Biomacromolecules to Their Adherence and Mechanics

In this work, the contributions of the pathogenic Listeria monocytogenes cell-wall biomacromolecules to the bacterial mechanics and adhesion to a model inert surface of silicon nitride in water were investigated by atomic force microscopy. Chemical ethylenediaminetetraacetic acid (EDTA) and biological enzymatic trypsin treatments of cells were performed to partially or totally remove the bacterial cell-wall proteins and carbohydrates. Removal of 48.2% proteins and 29.2% of carbohydrates from the cell-wall of the bacterium by the EDTA treatment resulted in a significant decrease in the length of the bacterial cell-wall biomacromolecules and an increase in the rigidity of the bacterial cells as predicted from fitting a model of steric repulsion to the force-distance approach data and classic Hertz model to the indentation-force data, respectively. In comparison, removal of almost all the cell-wall proteins (99.5% removal) and 8.6% of cell-wall carbohydrates by the trypsin treatment resulted in an increase in the elasticity of the bacterial cells, an increase in the extension of the cell-wall biomacromolecules, and a significant decrease in their apparent grafting densities. In addition, adhesion strength of native-untreated L. monocytogenes to silicon nitride in water decreased by 30% on average after the EDTA treatment and further decreased by 60% on average after the trypsin treatment, showing a positive correlation with the% removal of cell-wall proteins by the EDTA and trypsin treatments, respectively.

Fungal spore adhesion on glycidoxypropyltrimethoxy silane modified silica nanoparticle surfaces as revealed by single cell force spectroscopy

Thin film coatings prepared from commercially available glycidoxypropyltrimethoxysilane (GPS) modified silica nanoparticles (SiNPs) (Bindzil® CC301 and Bindzil® CC302) have previously shown excellent antifouling performance against a broad range of microbes [Molino et al., "Hydration layer structure of biofouling-resistant nanoparticles," ACS Nano 12, 11610 (2018)]. In this work, single cell force spectroscopy (SCFS) was used to measure the biological interactions between Epicoccum nigrum fungal spores and the same silica nanoparticle-based surfaces used in the aforementioned study, including a: glass coverslip, unmodified SiNP coatings, and both low (Bindzil® CC301) and high density (CC302) GPS functionalized SiNP coatings as a function of NaCl concentration. From the SCFS curves, the spore adhesion to the surface was greatest on the glass coverslip (20-80 nN) followed by the unmodified SiNP (3-5 nN) across all salt concentrations. Upon approach to both surfaces, the spores showed a long-range attraction generally with a profile characteristic of biointeractions and likely those of the outer cell wall structures or biological constituents. The attractive force allowed the spores to initially adhere to the surface and was found to be linearly proportional to the spore adhesion. In comparison, both high and low density GPS-SINP significantly reduced the spore adhesion (0.5-0.9 nN). In addition, the spore adhesion on high density GPS-SiNP occurred in only 14%-27% of SCFS curves (40%-48% for low density GPS-SiNP) compared to 83%-97% for the unmodified SiNP, indicating that in most cases the GPS functionalization completely prevented spore adhesion. The GPS-SiNP surfaces conversely showed a long-range electrostatic repulsion at low 1mM NaCl that was replaced by short-range repulsion at the higher salt concentrations. From the findings, it is proposed that the attractive force is a critical step in initial adhesion processes of the spore. The effective antifouling properties of the GPS are attributed to the ability to negate the attractive forces, either through electrostatic repulsion in low salt conditions and primarily from short-range repulsion correlating to the previously reported combined steric-hydration effect of the GPS functionalization on SiNP coatings.

Using Atomic Force Microscopy To Illuminate the Biophysical Properties of Microbes

Since its invention in 1986, atomic force microscopy (AFM) has grown from a system designed for imaging inorganic surfaces to a tool used to probe the biophysical properties of living cells and tissues. AFM is a scanning probe technique and uses a pyramidal tip attached to a flexible cantilever to scan across a surface, producing a highly detailed image. While many research articles include AFM images, fewer include force-distance curves, from which several biophysical properties can be determined. In a single force-distance curve, the cantilever is lowered and raised from the surface, while the forces between the tip and the surface are monitored. Modern AFM has a wide variety of applications, but this review will focus on exploring the mechanobiology of microbes, which we believe is of particular interest to those studying biomaterials. We briefly discuss experimental design as well as different ways of extracting meaningful values related to cell surface elasticity, cell stiffness, and cell adhesion from force-distance curves. We also highlight both classic and recent experiments using AFM to illuminate microbial biophysical properties.

The clinical Biofilm Ring Test: a promising tool for the clinical assessment of biofilm-producing Candida species

Candida species are opportunistic pathogens responsible for a variety of diseases, ranging from skin and mucosal lesions to severe systemic, life-threatening infections. Candida albicans accounts for more than 70% of all Candida infections, however, the clinical relevance of other species such as Candida parapsilosis and Candida krusei are being increasingly recognized. Biofilm-producing yeasts cells acquire an increased resistance to antifungal agents, often leading to therapeutic failure and chronic infection. Conventional methods such as crystal violet (CV) and tetrazolium (XTT) reduction assay, developed to evaluate biofilm formation in Candida species are usually time-consuming, present a high intra- and inter-assay variability of the results and are therefore hardly applicable to routine diagnostics. This study describes an in-vitro assay developed for the measurement of biofilm formation in Candida species based on the clinical Biofilm Ring Test® (cBRT). We found a significant concordance between the cBRT and both CV (k = 0.74) and XTT (k = 0.62), respectively. Nevertheless, the cBRT resulted more reliable and reproducible than CV and XTT, requiring a minimal sample manipulation and allowing a high throughput assessment, directly on viable cells. The results indicate that the cBRT may provide a suitable, cost-effective technique for routine biofilm testing in clinical microbiology.

Detrimental impact of silica nanoparticles on the nanomechanical properties of Escherichia coli, studied by AFM

Despite great innovative and technological promises, nanoparticles (NPs) can ultimately exert an antibacterial activity by affecting the cell envelope integrity. This envelope, by conferring the cell its rigidity and protection, is intimately related to the mechanical behavior of the bacterial surface. Depending on their size, surface chemistry, shape, NPs can induce damages to the cell morphology and structure among others, and are therefore expected to alter the overall mechanical properties of bacteria. Although Atomic Force Microscopy (AFM) stands as a powerful tool to study biological systems, with high resolution and in near physiological environment, it has rarely been applied to investigate at the same time both morphological and mechanical degradations of bacteria upon NPs treatment. Consequently, this study aims at quantifying the impact of the silica NPs (SiO₂-NPs) on the mechanical properties of E. coli cells after their exposure, and relating it to their toxic activity under a critical diameter. Cell elasticity was calculated by fitting the force curves with the Hertz model, and was correlated with the morphological study. SiO₂-NPs of 100 nm diameter did not trigger any significant change in the Young modulus of E. coli, in agreement with the bacterial intact morphology and membrane structure. On the opposite, the 4 nm diameter SiO₂-NPs did induce a significant decrease in E. coli Young modulus, mainly associated with the disorganization of lipopolysaccharides in the outer membrane and the permeation of the underlying peptidoglycan layer. The subsequent toxic behavior of these NPs is finally confirmed by the presence of membrane residues, due to cell lysis, exhibiting typical adhesion features.

Layered Structure and Complex Mechanochemistry Underlie Strength and Versatility in a Bacterial Adhesive

While designing synthetic adhesives that perform in aqueous environments has proven challenging, microorganisms commonly produce bioadhesives that efficiently attach to a variety of substrates, including wet surfaces. The aquatic bacterium Caulobacter crescentus uses a discrete polysaccharide complex, the holdfast, to strongly attach to surfaces and resist flow. The holdfast is extremely versatile and has impressive adhesive strength. Here, we used atomic force microscopy in conjunction with superresolution microscopy and enzymatic assays to unravel the complex structure of the holdfast and to characterize its chemical constituents and their role in adhesion. Our data support a model whereby the holdfast is a heterogeneous material organized as two layers: a stiffer nanoscopic core layer wrapped into a sparse, far-reaching, flexible brush layer. Moreover, we found that the elastic response of the holdfast evolves after surface contact from initially heterogeneous to more homogeneous. From a composition point of view, besides N-acetyl-d-glucosamine (NAG), the only component that had been identified to date, our data show that the holdfast contains peptides and DNA. We hypothesize that, while polypeptides are the most important components for adhesive force, the presence of DNA mainly impacts the brush layer and the strength of initial adhesion, with NAG playing a primarily structural role within the core. The unanticipated complexity of both the structure and composition of the holdfast likely underlies its versatility as a wet adhesive and its distinctive strength. Continued improvements in understanding of the mechanochemistry of this bioadhesive could provide new insights into how bacteria attach to surfaces and could inform the development of new adhesives.IMPORTANCE There is an urgent need for strong, biocompatible bioadhesives that perform underwater. To strongly adhere to surfaces and resist flow underwater, the bacterium Caulobacter crescentus produces an adhesive called the holdfast, the mechanochemistry of which remains undefined. We show that the holdfast is a layered structure with a stiff core layer and a polymeric brush layer and consists of polysaccharides, polypeptides, and DNA. The DNA appears to play a role in the structure of the brush layer and initial adhesion, the peptides in adhesive strength, and the polysaccharides in the structure of the core. The complex, multilayer organization and diverse chemistry described here underlie the distinctive adhesive properties of the holdfast and will provide important insights into the mechanisms of bacterial adhesion and bioadhesive applications.

Advances in in Vitro and in Vivo Models for Studying the Staphylococcal Factors Involved in Implant Infections

Implant infections due to staphylococci are one of the greatest threats facing patients receiving implant devices. For many years researchers have sought to understand the mechanisms involved in the adherence of the bacterium to the implanted device and the formation of the unique structure, the biofilm, which protects the indwelling bacteria from the host defence and renders them resistant to antibiotic treatment. A major goal has been to develop in vitro and in vivo models that adequately reflect the real-life situation. From the simple microtiter plate assay and scanning electron microscopy, tools for studying adherence and biofilm formation have since evolved to include specialised equipment for studying adherence, flow cell systems, real-time analysis of biofilm formation using reporter gene assays both in vitro and in vivo, and a wide variety of animal models. In this article, we discuss advances in the last few years in selected in vitro and in vivo models as well as future developments in the study of adherence and biofilm formation by the staphylococci.

Methods of Micropatterning and Manipulation of Cells for Biomedical Applications

Micropatterning and manipulation of mammalian and bacterial cells are important in biomedical studies to perform in vitro assays and to evaluate biochemical processes accurately, establishing the basis for implementing biomedical microelectromechanical systems (bioMEMS), point-of-care (POC) devices, or organs-on-chips (OOC), which impact on neurological, oncological, dermatologic, or tissue engineering issues as part of personalized medicine. Cell patterning represents a crucial step in fundamental and applied biological studies in vitro, hence today there are a myriad of materials and techniques that allow one to immobilize and manipulate cells, imitating the 3D in vivo milieu. This review focuses on current physical cell patterning, plus chemical and a combination of them both that utilizes different materials and cutting-edge micro-nanofabrication methodologies.

The Emerging Pathogen Candida auris: Growth Phenotype, Virulence Factors, Activity of Antifungals, and Effect of SCY-078, a Novel Glucan Synthesis Inhibitor, on Growth Morphology and Biofilm Formation

Candidaauris, a new multidrug-resistant Candida spp. which is associated with invasive infection and high rates of mortality, has recently emerged. Here, we determined the virulence factors (germination, adherence, biofilm formation, phospholipase and proteinase production) of 16 C. auris isolates and their susceptibilities to 11 drugs belonging to different antifungal classes, including a novel orally bioavailable 1,3-β-d-glucan synthesis inhibitor (SCY-078). We also examined the effect of SCY-078 on the growth, ultrastructure, and biofilm-forming abilities of C. auris. Our data showed that while the tested strains did not germinate, they did produce phospholipase and proteinase in a strain-dependent manner and had a significantly reduced ability to adhere and form biofilms compared to that of Candida albicans (P = 0.01). C. auris isolates demonstrated reduced susceptibility to fluconazole and amphotericin B, while, in general, they were susceptible to the remaining drugs tested. SCY-078 had an MIC₉₀ of 1 mg/liter against C. auris and caused complete inhibition of the growth of C. auris and C. albicans. Scanning electron microscopy analysis showed that SCY-078 interrupted C. auris cell division, with the organism forming abnormal fused fungal cells. Additionally, SCY-078 possessed potent antibiofilm activity, wherein treated biofilms demonstrated significantly reduced metabolic activity and a significantly reduced thickness compared to the untreated control (P < 0.05 for both comparisons). Our study shows that C. auris expresses several virulence determinants (albeit to a lesser extent than C. albicans) and is resistant to fluconazole and amphotericin B. SCY-078, the new orally bioavailable antifungal, had potent antifungal/antibiofilm activity against C. auris, indicating that further evaluation of this antifungal is warranted.

The Emerging Pathogen Candida auris: Growth Phenotype, Virulence Factors, Activity of Antifungals, and Effect of SCY-078, a Novel Glucan Synthesis Inhibitor, on Growth Morphology and Biofilm Formation

Candidaauris, a new multidrug-resistant Candida spp. which is associated with invasive infection and high rates of mortality, has recently emerged. Here, we determined the virulence factors (germination, adherence, biofilm formation, phospholipase and proteinase production) of 16 C. auris isolates and their susceptibilities to 11 drugs belonging to different antifungal classes, including a novel orally bioavailable 1,3-β-d-glucan synthesis inhibitor (SCY-078). We also examined the effect of SCY-078 on the growth, ultrastructure, and biofilm-forming abilities of C. auris Our data showed that while the tested strains did not germinate, they did produce phospholipase and proteinase in a strain-dependent manner and had a significantly reduced ability to adhere and form biofilms compared to that of Candida albicans (P = 0.01). C. auris isolates demonstrated reduced susceptibility to fluconazole and amphotericin B, while, in general, they were susceptible to the remaining drugs tested. SCY-078 had an MIC₉₀ of 1 mg/liter against C. auris and caused complete inhibition of the growth of C. auris and C. albicans Scanning electron microscopy analysis showed that SCY-078 interrupted C. auris cell division, with the organism forming abnormal fused fungal cells. Additionally, SCY-078 possessed potent antibiofilm activity, wherein treated biofilms demonstrated significantly reduced metabolic activity and a significantly reduced thickness compared to the untreated control (P < 0.05 for both comparisons). Our study shows that C. auris expresses several virulence determinants (albeit to a lesser extent than C. albicans) and is resistant to fluconazole and amphotericin B. SCY-078, the new orally bioavailable antifungal, had potent antifungal/antibiofilm activity against C. auris, indicating that further evaluation of this antifungal is warranted.

Multiscale Model Describing Bacterial Adhesion and Detachment

Bacterial surfaces are complex structures with nontrivial adhesive properties. The physics of bacterial adhesion deviates from that of ideal colloids as a result of cell-surface roughness and because of the mechanical properties of the polymers covering the cell surface. In the present study, we develop a simple multiscale model for the interplay between the potential energy functions that characterize the cell surface biopolymers and their interaction with the extracellular environment. We then use the model to study a discrete network of bonds in the presence of significant length heterogeneities in cell-surface polymers. The model we present is able to generate force curves (both approach and retraction) that closely resemble those measured experimentally. Our results show that even small-length-scale heterogeneities can lead to macroscopically nonlinear behavior that is qualitatively and quantitatively different from the homogeneous case. We also report on the energetic consequences of such structural heterogeneity.

Microbial colonisation of transparent glass-like carbon films triggered by a reversible radiation-induced hydrophobic to hydrophilic transition

Vacuum ultraviolet irradiation induces a wettability transition in glass-like carbon films, which renders their surface highly prone to microbial colonisation.

Bacterially Antiadhesive, Optically Transparent Surfaces Inspired from Rice Leaves

Because of the growing prevalence of antimicrobial resistance strains, there is an increasing need to develop material surfaces that prevent bacterial attachment and contamination in the absence of antibiotic agents. Herein, we present bacterial antiadhesive materials inspired from rice leaves. "Rice leaf-like surfaces" (RLLS) were fabricated by a templateless, self-masking reactive-ion etching approach. Bacterial attachment on RLLS was characterized under both static and dynamic conditions using Gram-negative Escherichia coli O157:H7 and Gram-positive Staphylococcus aureus. RLLS surfaces showed exceptional bacterial antiadhesion properties with a >99.9% adhesion inhibition efficiency. Furthermore, the optical properties of RLLS were investigated using UV-vis-NIR spectrophotometry. In contrast to most other bacterial antiadhesive surfaces, RLLS demonstrated optical-grade transparency (i.e., ≥92% transmission). We anticipate that the combination of bacterial antiadhesion efficiency, optical grade transparency, and the convenient single-step method of preparation makes RLLS a very attractive candidate for the surfaces of biosensors; endoscopes; and microfluidic, bio-optical, lab-on-a-chip, and touchscreen devices.

The dynamics and pH-dependence of Ag43 adhesins' self-association probed by atomic force spectroscopy

Self-associating auto-transporter (SAAT) adhesins are two-domain cell surface proteins involved in bacteria auto-aggregation and biofilm formation. Antigen 43 (Ag43) is a SAAT adhesin commonly found in Escherichia coli whose variant Ag43a has been shown to promote persistence of uropathogenic E. coli within the bladder. The recent resolution of the tri-dimensional structure of the 499 amino-acids' β-domain in Ag43a has shed light on the possible mechanism governing the self-recognition of SAAT adhesins, in particular the importance of trans-interactions between the L shaped β-helical scaffold of two α-domains of neighboring adhesins. In this study, we use single-molecule force spectroscopy (SMFS) and dynamic force spectroscopy (DFS) to unravel the dynamics of Ag43-self association under various pH and molecular elongation rate conditions that mimic the situations encountered by E. coli in its natural environment. Results evidenced an important stretchability of Ag43α with unfolding of sub-domains leading to molecular extension as long as 150 nm. Nanomechanical analysis of molecular stretching data suggested that self-association of Ag43 can lead to the formation of dimers and tetramers driven by rapid and weak cis- as well as slow but strong trans-interaction forces with a magnitude as large as 100-250 pN. The dynamics of cis- and trans-interactions were demonstrated to be strongly influenced by pH and applied shear force, thus suggesting that environmental conditions can modulate Ag43-mediated aggregation of bacteria at the molecular level.

A concise review of nanoscopic aspects of bioleaching bacteria-mineral interactions

Bioleaching is a technology for the recovery of metals from minerals by means of microorganisms, which accelerate the oxidative dissolution of the mineral by regenerating ferric ions. Bioleaching processes take place at the interface of bacteria, sulfide mineral and leaching solution. The fundamental forces between a bioleaching bacterium and mineral surface are central to understanding the intricacies of interfacial phenomena, such as bacterial adhesion or detachment from minerals and the mineral dissolution. This review focuses on the current state of knowledge in the colloidal aspect of bacteria-mineral interactions, particularly for bioleaching bacteria. Special consideration is given to the microscopic structure of bacterial cells and the atomic force microscopy technique used in the quantification of fundamental interaction forces at nanoscale.

Single-cell force spectroscopy of bacteria enabled by naturally derived proteins

Bringing the study of bacterial adhesion down to a single-cell level is critical for understanding the molecular mechanisms involved in initial bacterial attachment. We have developed a simple and versatile method for making single-cell bacterial probes to study the adhesion of single bacterial cells by atomic force microscopy (AFM). A single-cell probe was made by picking up a bacterial cell from a glass surface using a tipless AFM cantilever coated with a commercial cell adhesive Cell-Tak. The method was applied to four different bacterial strains, and single-cell adhesion was measured on three surfaces (fresh glass, hydrophilic glass, and mica). Attachment to the cantilever was stable during the AFM force measurements that were conducted for 2 h, and viability was confirmed by Live/Dead fluorescence staining at the end of each experiment. The adhesion force and final rupture length were dependent on bacterial strains, surfaces properties, and contact time. The single-cell probe offers control of cell immobilization and thus holds advantages over the commonly used multicell probes with which random immobilization is obtained by submerging the cantilever in a bacterial suspension. The reported method provides a general platform for investigating single-cell interactions of bacteria with different surfaces and other cells by AFM force spectroscopy, thus improving our understanding of the mechanisms of bacterial attachment.

Viscous nature of the bond between adhering bacteria and substratum surfaces probed by atomic force microscopy

Here we report on the viscous nature of the bond between adhering bacteria and a substratum surface. A tailor-made script was written for an atomic force microscope, that enabled a constant loading force of 1 or 5 nN to act for 30 s upon a bacterium compressed between a cantilever and a glass surface, while measuring its deformation. Time-dependent deformation was fitted to a one element Kelvin-Voigt analogue of the bond to yield a characteristic relaxation time and viscosity of the bond. Viscosities of streptococcal bonds were smaller (<20 kPa s) than those of staphylococcal bonds (>31 kPa s). Since staphylococci are relatively rich in extracellular polymeric substances, it can be inferred that the presence of extracellular polymeric substances yields the major contribution to the viscous response. The viscous nature of the bond between adhering bacteria and substratum surfaces provides the bacteria with more time to respond and protect themselves against external stresses.

Antibiotic delivery potential of nano- and micro-porous marine structure-derived β-tricalcium phosphate spheres for medical applications

AIMS

This study gives a detailed evaluation of the antibiotic potential of a marine structure-based new drug delivery system produced by hydrothermally converting foraminifera exoskeletons to β-tricalcium phosphate (β-TCP) to treat clinical strain Staphylococcus aureus (MW2).

MATERIALS & METHODS

Foraminifera precursor materials were hydrothermally converted at 250°C for 48 h to produce β-TCP and loaded with gentamicin sulfate by adsorption for 24 h. The physicochemical properties of the material were characterized by scanning electron microscopy, powder x-ray diffraction and for pore size distribution profiles. The antibacterial efficacy of the system was tested for inhibition of S. aureus growth and in vitro cellular behavior were tested with human osteoblast cells (MG63) for cell viability.

DISCUSSION

Pore size distribution profiles showed that the structure allows the uniform distribution of nanopores of 1.5 nm and micropores of approximately 5 µm. The in vitro release profile indicates an initial burst release of 5% of total incorporated gentamicin. A time-delayed antibacterial efficacy test was designed to introduce the bacteria at predetermined time intervals from 0 to 60 min and showed that gentamicin prevents S. aureus grown in the same culture within 30 min, with no evidence of bacterial regrowth within 24 h. Human osteoblast cell (MG63) studies showed no detrimental effect on cell viability.

CONCLUSION

In the light of these results nano- and micro-pores containing β-TCP spheres show promise as potential bone void filler particles with antibacterial effects.

Forces driving the attachment of Staphylococcus epidermidis to fibrinogen-coated surfaces

Cell surface proteins of bacteria play essential roles in mediating the attachment of pathogens to host tissues and, therefore, represent key targets for anti-adhesion therapy. In the opportunistic pathogen Staphylococcus epidermidis , the adhesion protein SdrG mediates attachment of bacteria to the blood plasma protein fibrinogen (Fg) through a binding mechanism that is not yet fully understood. We report the direct measurement of the forces driving the adhesion of S. epidermidis to Fg-coated substrates using single-cell force spectroscopy. We found that the S. epidermidis -Fg adhesion force is of ~150 pN magnitude and that the adhesion strength and adhesion probability strongly increase with the interaction time, suggesting that the adhesion process involves time-dependent conformational changes. Control experiments with mutant bacteria lacking SdrG and substrates coated with the Fg β(6-20) peptide, instead of the full Fg protein, demonstrate that these force signatures originate from the rupture of specific bonds between SdrG and its peptide ligand. Collectively, our results are consistent with a dynamic, multi-step ligand-binding mechanism called "dock, lock, and latch".

Single-Cell Force Spectroscopy of Als-Mediated Fungal Adhesion

Macroscopic assays that are traditionally used to investigate the adhesion behaviour of microbial cells provide averaged information obtained on large populations of cells and do not measure the fundamental forces driving single-cell adhesion. Here, we use single-cell force spectroscopy (SCFS) to quantify the specific and non-specific forces engaged in the adhesion of the human fungal pathogen Candida albicans. Saccharomyces cerevisiae cells expressing the C. albicans adhesion protein Als5p were attached on atomic force microscopy tipless cantilevers using a bioinspired polydopamine wet polymer, and force-distance curves were recorded between the obtained cell probes and various solid surfaces. Force signatures obtained on hydrophobic substrates exhibited large adhesion forces (1.25 ± 0.2 nN) with extended rupture lengths (up to 400 nm), attributed to the binding and stretching of the hydrophobic tandem repeats of Als5p. Data collected on fibronectin (Fn) -coated substrates featured strong adhesion forces (2.8 ± 0.6 nN), reflecting specific binding between Fn and the N-terminal immunoglobulin-like regions of Als5p, followed by weakly adhesive macromolecular bonds. Both hydrophobic and Fn adhesion forces increased with contact time, emphasizing the important role that time plays in strengthening adhesion. Our SCFS methodology provides a versatile platform in biomedicine for understanding the fundamental forces driving adhesion and biofilm formation in fungal pathogens.

Conceivable Bioremediation Techniques Based on Quorum Sensing

Quorum sensing(QS) is a mechanism of microbes to coordinate their activities, which allows them to function as multi-cellular systems. Recently, many researches have proved that the engineered QS system have a wide range of applications such as bioremediation of oil and heavy metal contaminated soils, and prevention of biofouling. Here we review the function of QS signals produced by bacteria, and the principle of enhancing degradative capacities of microbe. Specifically, we describe how QS system regulate the formation and dispersion of biofilms, which are reversible process that biofilms may be generated and removed as desired. The development of strategies to disrupt and manipulate QS are also implicated. Cells can be engineered to secrete QS signals to affect the behavior of neighboring cells in a consortium via engineered cellular communication. The complete genetic basis of QS may be used to control these communities of associated cells for bioremediation applications.

Bacterial attachment on sub-nanometrically smooth titanium substrata

Despite the volume of work that has been conducted on the topic, the role of surface topography in mediating bacterial cell adhesion is not well understood. The primary reason for this lack of understanding is the relatively limited extent of topographical characterisation employed in many studies. In the present study, the topographies of three sub-nanometrically smooth titanium (Ti) surfaces were comprehensively characterised, using nine individual parameters that together describe the height, shape and distribution of their surface features. This topographical analysis was then correlated with the adhesion behaviour of the pathogenic bacteria Staphylococcus aureus and Pseudomonas aeruginosa, in an effort to understand the role played by each aspect of surface architecture in influencing bacterial attachment. While P. aeruginosa was largely unable to adhere to any of the three sub-nanometrically smooth Ti surfaces, the extent of S. aureus cell attachment was found to be greater on surfaces with higher average, RMS and maximum roughness and higher surface areas. The cells also attached in greater numbers to surfaces that had shorter autocorrelation lengths and skewness values that approached zero, indicating a preference for less ordered surfaces with peak heights and valley depths evenly distributed around the mean plane. Across the sub-nanometrically smooth range of surfaces tested, it was shown that S. aureus more easily attached to surfaces with larger features that were evenly distributed between peaks and valleys, with higher levels of randomness. This study demonstrated that the traditionally employed amplitudinal roughness parameters are not the only determinants of bacterial adhesion, and that spatial parameters can also be used to predict the extent of attachment.

The role of growth temperature in the adhesion and mechanics of pathogenic L. monocytogenes: an AFM study

The adhesion strengths of pathogenic L. monocytogenes EGDe to a model surface of silicon nitride were quantified using atomic force microscopy (AFM) in water for cells grown under five different temperatures (10, 20, 30, 37, and 40 °C). The temperature range investigated was chosen to bracket the thermal conditions in which L. monocytogenes survive in the environment. Our results indicated that adhesion force and energy quantified were at their maximum when the bacteria were grown at 30 °C. The higher adhesion observed at 30 °C compared to the adhesion quantified for bacterial cells grown at 37, 40, 20, and 10 °C was associated with longer and denser bacterial surface biopolymer brushes as predicted from fitting a model of steric repulsion to the approach distance-force data as well from the results of protein colorimetric assays. Theoretically predicted adhesion energies based on soft-particle DLVO theory agreed well with the adhesion energies computed from AFM force-distance retraction data (r(2) = 0.94); showing a minimum energy barrier to adhesion at 30 °C.

Bacterial surface appendages strongly impact nanomechanical and electrokinetic properties of Escherichia coli cells subjected to osmotic stress

The physicochemical properties and dynamics of bacterial envelope, play a major role in bacterial activity. In this study, the morphological, nanomechanical and electrohydrodynamic properties of Escherichia coli K-12 mutant cells were thoroughly investigated as a function of bulk medium ionic strength using atomic force microscopy (AFM) and electrokinetics (electrophoresis). Bacteria were differing according to genetic alterations controlling the production of different surface appendages (short and rigid Ag43 adhesins, longer and more flexible type 1 fimbriae and F pilus). From the analysis of the spatially resolved force curves, it is shown that cells elasticity and turgor pressure are not only depending on bulk salt concentration but also on the presence/absence and nature of surface appendage. In 1 mM KNO(3), cells without appendages or cells surrounded by Ag43 exhibit large Young moduli and turgor pressures (∼700-900 kPa and ∼100-300 kPa respectively). Under similar ionic strength condition, a dramatic ∼50% to ∼70% decrease of these nanomechanical parameters was evidenced for cells with appendages. Qualitatively, such dependence of nanomechanical behavior on surface organization remains when increasing medium salt content to 100 mM, even though, quantitatively, differences are marked to a much smaller extent. Additionally, for a given surface appendage, the magnitude of the nanomechanical parameters decreases significantly when increasing bulk salt concentration. This effect is ascribed to a bacterial exoosmotic water loss resulting in a combined contraction of bacterial cytoplasm together with an electrostatically-driven shrinkage of the surface appendages. The former process is demonstrated upon AFM analysis, while the latter, inaccessible upon AFM imaging, is inferred from electrophoretic data interpreted according to advanced soft particle electrokinetic theory. Altogether, AFM and electrokinetic results clearly demonstrate the intimate relationship between structure/flexibility and charge of bacterial envelope and propensity of bacterium and surface appendages to contract under hypertonic conditions.

Bacterial capture efficiency and antimicrobial activity of phage-functionalized model surfaces

The rise of antibiotic-resistant bacteria has directed substantial attention toward the use of bacteriophages as a means to control bacterial populations. It has been proposed that bacteriophages can be applied as a coating on surfaces in healthcare settings or on indwelling medical devices to create an antimicrobial surface. In this study, antimicrobial model surfaces functionalized with five different types of bacteriophage were prepared and characterized with X-ray photoelectron spectroscopy and atomic force microscopy. The bacterial capture efficiency of these functionalized surfaces was studied for two common bacteria, Escherichia coli and Salmonella typhimurium. Binding of the phages to a solid surface affected their biofunctionality as expressed by the capture efficiency and rate of host membrane disruption. Moreover, the size and shape of the bacteriophage and positioning of its specific binding proteins significantly affected its bacterial capture capability in the immobilized state. Symmetric bacteriophages were found to be a better choice for antibacterial surfaces compared to more asymmetric tailed bacteriophages. Immobilized phages were found to disrupt the membranes of attached bacteria and are thus proposed as a candidate for antimicrobial surfaces.

Atomic force microscopy investigations of heterogeneities in the adhesion energies measured between pathogenic and non-pathogenic Listeria species and silicon nitride as they correlate to virulence and adherence

Atomic force microscopy (AFM) was used to probe heterogeneities in adhesion energies measured between pathogenic and non-pathogenic species of Listeria and silicon nitride in water at four levels. Adhesion energies were quantified on individual bacterial cells (cell level), bacterial cells that belonged to an individual Listeria strain but varied in their cultures (strain level), bacterial cells that belonged to an individual Listeria species but varied in their strain type (species level) and on bacterial cells that belonged to the Listeria genus but varied in their species type (genus level). To quantify heterogeneities in the adhesion energies, a heterogeneity index (HI) was defined based on quantified standard errors of mean. At the cell level, spatial variations in the adhesion energies were not observed. For the strain, species, and genus levels, the HI increased with increased adhesion energies. At the species level, the HI increased with strain virulence.

Automated force volume image processing for biological samples

Atomic force microscopy (AFM) has now become a powerful technique for investigating on a molecular level, surface forces, nanomechanical properties of deformable particles, biomolecular interactions, kinetics, and dynamic processes. This paper specifically focuses on the analysis of AFM force curves collected on biological systems, in particular, bacteria. The goal is to provide fully automated tools to achieve theoretical interpretation of force curves on the basis of adequate, available physical models. In this respect, we propose two algorithms, one for the processing of approach force curves and another for the quantitative analysis of retraction force curves. In the former, electrostatic interactions prior to contact between AFM probe and bacterium are accounted for and mechanical interactions operating after contact are described in terms of Hertz-Hooke formalism. Retraction force curves are analyzed on the basis of the Freely Jointed Chain model. For both algorithms, the quantitative reconstruction of force curves is based on the robust detection of critical points (jumps, changes of slope or changes of curvature) which mark the transitions between the various relevant interactions taking place between the AFM tip and the studied sample during approach and retraction. Once the key regions of separation distance and indentation are detected, the physical parameters describing the relevant interactions operating in these regions are extracted making use of regression procedure for fitting experiments to theory. The flexibility, accuracy and strength of the algorithms are illustrated with the processing of two force-volume images, which collect a large set of approach and retraction curves measured on a single biological surface. For each force-volume image, several maps are generated, representing the spatial distribution of the searched physical parameters as estimated for each pixel of the force-volume image.

Oral consumption of cranberry juice cocktail inhibits molecular-scale adhesion of clinical uropathogenic Escherichia coli

Cranberry juice cocktail (CJC) has been shown to inhibit the formation of biofilm by uropathogenic Escherichia coli. In order to investigate whether the anti-adhesive components could reach the urinary tract after oral consumption of CJC, a volunteer was given 16 oz of either water or CJC. Urine samples were collected at 0, 2, 4, 6, and 8 hours after consumption of a single dose. The ability of compounds in the urine to influence bacterial adhesion was tested for six clinical uropathogenic E. coli strains, including four P-fimbriated strains (B37, CFT073, BF1023, and J96) and two strains not expressing P-fimbriae but exhibiting mannose-resistant hemagglutination (B73 and B78). A non-fimbriated strain, HB101, was used as a control. Atomic force microscopy (AFM) was used to measure the adhesion force between a silicon nitride probe and bacteria treated with urine samples. Within 2 hours after CJC consumption, bacteria of the clinical strains treated with the corresponding urine sample demonstrated lower adhesion forces than those treated with urine collected before CJC consumption. The adhesion forces continued decreasing with time after CJC consumption over the 8-hour measurement period. The adhesion forces of bacteria after exposure to urine collected following water consumption did not change. HB101 showed low adhesion forces following both water and CJC consumption, and these did not change over time. The AFM adhesion force measurements were consistent with the results of a hemagglutination assay, confirming that oral consumption of CJC could act against adhesion of uropathogenic E. coli.

Role of persister cells in chronic infections: clinical relevance and perspectives on anti-persister therapies

Certain infectious diseases caused by pathogenic bacteria are typically chronic in nature. Potentially deadly examples include tuberculosis, caused by Mycobacterium tuberculosis, cystic fibrosis-associated lung infections, primarily caused by Pseudomonas aeruginosa, and candidiasis, caused by the fungal pathogen Candida albicans. A hallmark of this type of illness is the recalcitrance to treatment with antibiotics, even in the face of laboratory tests showing the causative agents to be sensitive to drugs. Recent studies have attributed this treatment failure to the presence of a small, transiently multidrug-tolerant subpopulation of cells, so-called persister cells. Here, we review our current understanding of the role that persisters play in the treatment and outcome of chronic infections. In a second part, we offer a perspective on the development of anti-persister therapies based on genes and mechanisms that have been implicated in persistence over the last decade.

Nanoscale investigation on E. coli adhesion to modified silicone surfaces

Bacterial infection is a major challenge in biomaterials development. The adhesion of microorganisms to the material surface is the first step in infectious conditions and this quickly leads to the formation of biofilms on a material surface. A unique attribute of atomic force microscopy (AFM) is that it reveals not only the morphology of cells and the surface roughness of the substrate, but it can also quantify the adhesion force between bacteria and surfaces. We have shown that fluoroalkylsilane (FAS) and octadecyltrichlorosilane (OTS)-coated silicone samples exhibit greater potential for reducing E. coli JM 109 adhesion than heparin- and hyaluronan-modified samples. The force curves obtained from AFM can be used as a primary indicator in predicting bacterial adhesion.

Analysis of bacterial surface interactions using microfluidic systems

Modern microbiological research has increasingly focused on the interactions between bacterial cells and the surfaces that they inhabit. To this end, microfluidic devices have played a large role in enabling research of cell-surface interactions, especially surface attachment and biofilm formation. This review provides background on microfluidic devices and their use in biological systems, as well specific examples from current literature. Methods to observe and interrogate cells within microfluidic devices are described, as well as the analytical techniques that are used to collect these data.

Bacterial infection complications in children with cochlear implants in the Czech Republic

OBJECTIVE

Studies describing wound infections after cochlear implantation are rare. Meticulous operative techniques and sufficient surgical skill can help to avoid severe postoperative complications. Minor complications such as seromas, superficial wound infections, skin emphysema, and swelling can all be successfully treated using conservative methods. Serious problems, however, could be caused by Pseudomonas aeruginosa and Staphylococcus aureus infections.

STUDY DESIGN

Retrospective case series.

SETTING

Pediatric cochlear implant center in the Czech Republic.

RESULTS

In our cohort of 360 children operated on between 1994 and 2009, there were no major surgical complications. However, there were four serious wound infections, two of which resulted in explantation of the device. Two patients with a well-bordered abscess formation were successfully treated with antibiotics and drainage. Explantation was required in another two children with refractory P. aeruginosa infection. Despite favorable sensitivity to a number of antibiotics, intravenous and intensive local treatment failed. After explantation, the operative sites healed immediately. Both children were successfully implanted contralaterally 6 months later. Detailed bacteriological tests from different parts of the device were performed.

CONCLUSION

The consequences of explantation were discussed in our cochlear implant center. Confirmed by the microbiological results and reports in the scientific literature, it seems preferable to cut the electrode near the cochlear array and leave it inside the cochlea in order to use the same ear for reimplantation at a later date.

Applications of quorum sensing in biotechnology

Many unicellular microorganisms use small signaling molecules to determine their local concentration. The processes involved in the production and recognition of these signals are collectively known as quorum sensing (QS). This form of cell-cell communication is used by unicellular microorganisms to co-ordinate their activities, which allows them to function as multi-cellular systems. Recently, several groups have demonstrated artificial intra-species and inter-species communication through synthetic circuits which incorporate components of bacterial QS systems. Engineered QS-based circuits have a wide range of applications such as production of biochemicals, tissue engineering, and mixed-species fermentations. They are also highly useful in designing microbial biosensors to identify bacterial species present in the environment and within living organisms. In this review, we first provide an overview of bacterial QS systems and the mechanisms developed by bacteria and higher organisms to obstruct QS communications. Next, we describe the different ways in which researchers have designed QS-based circuits and their applications in biotechnology. Finally, disruption of quorum sensing is discussed as a viable strategy for preventing the formation of harmful biofilms in membrane bioreactors and marine transportation.

Our current understanding of fungal biofilms

Fungal biofilms are an escalating clinical problem associated with significant rates of mortality. Candida albicans is the most notorious of all fungal biofilm formers. However, non-Candida species, yeasts such as Cryptococcus neoformans, and filamentous moulds such as Aspergillus fumigatus, have been shown to be implicated in biofilm-associated infections. Fungal biofilms have distinct developmental phases, including adhesion, colonisation, maturation and dispersal, which are governed by complex molecular events. Recalcitrance to antifungal therapy remains the greatest threat to patients with fungal biofilms. This review discusses our current understanding of the basic biology and clinical implications associated with fungal biofilms.

Adhesion of spores of Bacillus thuringiensis on a planar surface

Adhesion of spores of Bacillus thuringiensis (Bt) and spherical silica particles on surfaces was experimentally and theoretically investigated in this study. Topography analysis via atomic force microscopy (AFM) and electron microscopy indicates that Bt spores are rod shaped, approximately 1.3 mum in length and approximately 0.8 mum in diameter. The adhesion force of Bt spores and silica particles on gold-coated glass was measured at various relative humidity (RH) levels by AFM. It was expected that the adhesion force would vary with RH because the individual force components contributing to the adhesion force depend on RH. The adhesion force between a particle and a planar surface in atmospheric environments was modeled as the contribution of three major force components: capillary, van der Waals, and electrostatic interaction forces. Adhesion force measurements for Bt spore (silica particle) and the gold surface system were comparable with calculations. Modeling results show that there is a critical RH value, which depends on the hydrophobicity of the materials involved, below which the water meniscus does not form and the contribution of the capillary force is zero. As RH increases, the van der Waals force decreases while the capillary force increases to a maximum value.

Role of cranberry on bacterial adhesion forces and implications for Escherichia coli-uroepithelial cell attachment

Previous clinical research has suggested that the consumption of cranberry products prevents the adhesion of Escherichia coli to uroepithelial cells by causing changes in bacterial fimbriae. Atomic force microscopy was used to probe the adhesion forces between E. coli (nonfimbriated strain HB101 and the P-fimbriated variant HB101pDC1) and a model surface (silicon nitride), to determine the effect of growth in cranberry products on bacterial adhesion. Bacteria were grown in tryptic soy broth supplemented with either light cranberry juice cocktail (L-CJC) or cranberry proanthocyanidins (PACs). Growth of E. coli HB101pDC1 and HB101 in L-CJC or PACs resulted in a decrease in adhesion forces with increasing number of cultures. In a macroscale bacteria-uroepithelial cell adhesion assay a decrease in bacterial attachment was observed for E. coli HB101pDC1 grown in L-CJC or PACs. This effect was reversible because bacteria that were regrown in cranberry-free medium regained their ability to attach to uroepithelial cells, and their adhesion forces reverted to the values observed in the control condition. Exposure to increasing concentrations of L-CJC resulted in a decrease of bacterial attachment to uroepithelial cells for the P-fimbriated strain after L-CJC treatment (27% by weight) and after PACs treatment (345.8 microg/mL). Cranberry products affect the surface properties, such as fimbriae and lipopolysaccharides, and adhesion of fimbriated and nonfimbriated E. coli. The concentration of cranberry products and the number of cultures the bacteria were exposed to cranberry determines how much the adhesion forces and attachment are altered.