Quorum-sensing regulation of adhesion in Serratia marcescens MG1 is surface dependent

Serratia marcescens is an opportunistic pathogen and a major cause of ocular infections. In previous studies of S. marcescens MG1, we showed that biofilm maturation and sloughing were regulated by N-acyl homoserine lactone (AHL)-based quorum sensing (QS). Because of the importance of adhesion in initiating biofilm formation and infection, the primary goal of this study was to determine whether QS is important in adhesion to both abiotic and biotic surfaces, as assessed by determining the degree of attachment to hydrophilic tissue culture plates and human corneal epithelial (HCE) cells. Our results demonstrate that while adhesion to the abiotic surface was AHL regulated, adhesion to the HCE cell biotic surface was not. Type I fimbriae were identified as the critical adhesin for non-QS-mediated attachment to the biotic HCE cell surface but played no role in adhesion to the abiotic surface. While we were not able to identify a single QS-regulated adhesin essential for attachment to the abiotic surface, four AHL-regulated genes involved in adhesion to the abiotic surface were identified. Interestingly, two of these genes, bsmA and bsmB, were also shown to be involved in adhesion to the biotic surface in a non-QS-controlled fashion. Therefore, the expression of these two genes appears to be cocontrolled by regulators other than the QS system for mediation of attachment to HCE cells. We also found that QS in S. marcescens regulates other potential cell surface adhesins, including exopolysaccharide and the outer membrane protein OmpX. We concluded that S. marcescens MG1 utilizes different regulatory systems and adhesins in attachment to biotic and abiotic surfaces and that QS is a main regulatory pathway in adhesion to an abiotic surface but not in adhesion to a biotic surface.     

Protein-Mediated Adhesion of the Dissimilatory Fe(III)-Reducing Bacterium Shewanella alga BrY to Hydrous Ferric Oxide

The rate and extent of bacterial Fe(III) mineral reduction are governed by molecular-scale interactions between the bacterial cell surface and the mineral surface. These interactions are poorly understood. This study examined the role of surface proteins in the adhesion of Shewanella alga BrY to hydrous ferric oxide (HFO). Enzymatic degradation of cell surface polysaccharides had no effect on cell adhesion to HFO. The proteolytic enzymes Streptomyces griseus protease and chymotrypsin inhibited the adhesion of S. alga BrY cells to HFO through catalytic degradation of surface proteins. Trypsin inhibited S. alga BrY adhesion solely through surface-coating effects. Protease and chymotrypsin also mediated desorption of adhered S. alga BrY cells from HFO while trypsin did not mediate cell desorption. Protease removed a single peptide band that represented a protein with an apparent molecular mass of 50 kDa. Chymotrypsin removed two peptide bands that represented proteins with apparent molecular masses of 60 and 31 kDa. These proteins represent putative HFO adhesion molecules. S. alga BrY adhesion was inhibited by up to 46% when cells were cultured at sub-MICs of chloramphenicol, suggesting that protein synthesis is necessary for adhesion. Proteins extracted from the surface of S. alga BrY cells inhibited adhesion to HFO by up to 41%. A number of these proteins bound specifically to HFO, suggesting that a complex system of surface proteins mediates S. alga BrY adhesion to HFO.     

Models of normal and transformed cell adhesion,and capping and locomotion in vitro

It is proposed that patching, capping and endocytosis, and cell locomotion are manifestations of a single process whereby the cell discards foreign materials. Capping results from the binding to the cell surface of particulate (or molecular) objects which cannot function as immovable substratum. This might be described as unsuccessful or abortive cell adhesion in that the particles adhere to the cell rather than the cell adhering to the substratum. Lateral particle movements on the cell surface membrane are effected by the submembranous microfilament-microtubule system, resulting in capping without displacement of the cell. Successful adhesion of the cell to a substratum renders capping and endocytosis impossible and the cell attempts to discard the substratum by mechanisms analogous to capping. The cell achieves this by lateral movement and detachment of the trailing edge.The concept of abortive adhesion leading to capping has been amplified by the development of molecular models of normal and neoplastic cell adhesion in vitro in the presence and absence of serum. In these models, the normal cells have molecule A (adhesion sites) on their surface; they can spread on the substratum in the absence of serum. In the presence of serum, the A molecules on the normal cell surface bind with B molecules in serum, which may be substratum-bound or free in suspension. Binding of free B molecules with cell surface A molecules results in blockage of adhesion sites; these are cleared via capping. New adhesion sites (A molecules) are produced at the active edges of the cell. Binding of cell surface A molecules with the substratum bound B molecules results in cell adhesion. Transformed cells do not have A molecules on their surface; they cannot spread in the absence of serum. The transformed cells may recruit A molecules from the serum to attain deformability and spreading.These models also relate to capping of gold or resin particles, cell locomotion and regulation of cell division, and lectin-induced agglutination of transformed cells.     

The Effects of Leaf Roughness,Surface Free Energy and Work of Adhesion on Leaf Water Drop Adhesion

The adhesion of water droplets to leaves is important in controlling rainfall interception, and affects a variety of hydrological processes. Leaf water drop adhesion (hereinafter, adhesion) depends not only on droplet formulation and parameters but also on the physical (leaf roughness) and physico-chemical (surface free energy, its components, and work-of-adhesion) properties of the leaf surface. We selected 60 plant species from Shaanxi Province, NW China, as experimental materials with the goal of gaining insight into leaf physical and physico-chemical properties in relation to the adhesion of water droplets on leaves. Adhesion covered a wide range of area, from 4.09 to 88.87 g/m² on adaxial surfaces and 0.72 to 93.35 g/m² on abaxial surfaces. Distinct patterns of adhesion were observed among species, between adaxial and abaxial surfaces, and between leaves with wax films and wax crystals. Adhesion decreased as leaf roughness increased (r =  −0.615, p = 0.000), but there were some outliers, such as Salix psammophila and Populus simonii with low roughness and low adhesion, and the abaxial surface of Hyoscyamus pusillus and the adaxial surface of Vitex negundo with high roughness and high adhesion. Meanwhile, adhesion was positively correlated with surface free energy (r = 0.535, p = 0.000), its dispersive component (r = 0.526, p = 0.000), and work of adhesion for water (r = 0.698, p = 0.000). However, a significant power correlation was observed between adhesion and the polar component of surface free energy (p = 0.000). These results indicated that leaf roughness, surface free energy, its components, and work-of-adhesion for water played important roles in hydrological characteristics, especially work-of-adhesion for water.     

Quantitative Analyses of Force-Induced Amyloid Formation in Candida albicans Als5p: Activation by Standard Laboratory Procedures

Candida albicans adhesins have amyloid-forming sequences. In Als5p, these amyloid sequences cluster cell surface adhesins to create high avidity surface adhesion nanodomains. Such nanodomains form after force is applied to the cell surface by atomic force microscopy or laminar flow. Here we report centrifuging and resuspending S. cerevisiae cells expressing Als5p led to 1.7-fold increase in initial rate of adhesion to ligand coated beads. Furthermore, mechanical stress from vortex-mixing of Als5p cells or C. albicans cells also induced additional formation of amyloid nanodomains and consequent activation of adhesion. Vortex-mixing for 60 seconds increased the initial rate of adhesion 1.6-fold. The effects of vortex-mixing were replicated in heat-killed cells as well. Activation was accompanied by increases in thioflavin T cell surface fluorescence measured by flow cytometry or by confocal microscopy. There was no adhesion activation in cells expressing amyloid-impaired Als5p^V326N or in cells incubated with inhibitory concentrations of anti-amyloid dyes. Together these results demonstrated the activation of cell surface amyloid nanodomains in yeast expressing Als adhesins, and further delineate the forces that can activate adhesion in vivo. Consequently there is quantitative support for the hypothesis that amyloid forming adhesins act as both force sensors and effectors.     

Reproducible Biofilm Cultivation of Chemostat-Grown Escherichia coli and Investigation of Bacterial Adhesion on Biomaterials Using a Non-Constant-Depth Film Fermenter

Biomaterials-associated infections are primarily initiated by the adhesion of microorganisms on the biomaterial surfaces and subsequent biofilm formation. Understanding the fundamental microbial adhesion mechanisms and biofilm development is crucial for developing strategies to prevent such infections. Suitable in vitro systems for biofilm cultivation and bacterial adhesion at controllable, constant and reproducible conditions are indispensable. This study aimed (i) to modify the previously described constant-depth film fermenter for the reproducible cultivation of biofilms at non-depth-restricted, constant and low shear conditions and (ii) to use this system to elucidate bacterial adhesion kinetics on different biomaterials, focusing on biomaterials surface nanoroughness and hydrophobicity. Chemostat-grown Escherichia coli were used for biofilm cultivation on titanium oxide and investigating bacterial adhesion over time on titanium oxide, poly(styrene), poly(tetrafluoroethylene) and glass. Using chemostat-grown microbial cells (single-species continuous culture) minimized variations between the biofilms cultivated during different experimental runs. Bacterial adhesion on biomaterials comprised an initial lag-phase I followed by a fast adhesion phase II and a phase of saturation III. With increasing biomaterials surface nanoroughness and increasing hydrophobicity, adhesion rates increased during phases I and II. The influence of materials surface hydrophobicity seemed to exceed that of nanoroughness during the lag-phase I, whereas it was vice versa during adhesion phase II. This study introduces the non-constant-depth film fermenter in combination with a chemostat culture to allow for a controlled approach to reproducibly cultivate biofilms and to investigate bacterial adhesion kinetics at constant and low shear conditions. The findings will support developing and adequate testing of biomaterials surface modifications eventually preventing biomaterial-associated infections.     

Adhesion of conidia of the fungus Dilophospora alopecuri to the cuticle of the nematode Anguina agrostis,the vector in annual ryegrass toxicity

The adhesion of conidia of the fungus Dilophospora alopecuri to the surface of the second stage dauer larva (DL₂) of the nematode Anguina agrostis (syn. A. funesta) was examined using both light and electron optics. The process of attachment does not lead to any apparent damage to the epicuticle of the nematode. Photographs of sections cut tangentially through the setulose appendages of the conidia show that a mucilagenous fibrillar material appears to be exuded from the highly convoluted surface of these appendages. This material adheres to the surface of the nematode cuticle and is deposited in the transverse annulations. The adhesion of these spores to DL₂ of A. agrostis was examined in 4822 nematodes from four galls. The mean percentage of DL₂ with spores adhering was 64% and ranged from 43 to 85%. This adhesion was compared with that of Corynebacterium rathayi from bacterial galls and was found to coincide. Thus, bacteria adhere to nematodes with D. alopecuri conidia attached and these conidia adhere to nematodes with C rathayi attached. Furthermore, DL₂ that are free from conidial adhesion appear to be free from bacterial adhesion and, in most instances, DL₂ that remain from from bacterial adhesion remain free from conidial adhesion. These observations draw attention to the potential of D. alopecuri as an agent for the biological control of annual ryegrass toxicity. Conidial adhesion to A. agrostis differs from bacterial adhesion to this nematode in that no visible damage to the cuticle takes place. The concept that adhesion of microorganisms to nematodes occurs in two phases, one involving site recognition and the other, if it occurs, involving physiological interaction and morphological change is discussed.     

Determination of bacterial cell surface hydrophobicity of single cells in cultures and in wastewater in situ

Bacterial cell surface hydrophobicity is one of the most important factors that influence bacterial adhesion. A new method, microsphere adhesion to cells, for measuring bacterial cell surface hydrophobicity was developed. Microsphere adhesion to cells is based on microscopic enumeration of hydrophobic, fluorescent microspheres attaching to the bacterial surface. Cell surface hydrophobicity estimated by microsphere adhesion to cells correlates well with adhesion of bacteria to hydrocarbons or hydrophobic interaction chromatography for a set of hydrophilic and hydrophobic bacteria (linear correlation coefficients, R², were 0.845 and 0.981 respectively). We also used microsphere adhesion to cells to investigate the in situ properties of individual free-living bacteria directly in activated sludge. Results showed that the majority of the bacteria were hydrophilic, indicating the importance of cell surface hydrophobicity for bacterial adhesion in sludge, and for the overall success of the wastewater treatment process.     

The effect of cell surface components on adhesion ability of Lactobacillus rhamnosus

The aim of this study was to analyze the cell envelope components and surface properties of two phenotypes of Lactobacillus rhamnosus isolated from the human gastrointestinal tract. The ability of the bacteria to adhere to human intestinal cells and to aggregate with other bacteria was determined. L. rhamnosus strains E/N and PEN differed with regard to the presence of exopolysaccharides (EPS) and specific surface proteins. Transmission electron microscopy showed differences in the structure of the outer cell surface of the strains tested. Bacterial surface properties were analyzed by Fourier transform infrared spectroscopy, fatty acid methyl esters and hydrophobicity assays. Aggregation capacity and adhesion of the tested strains to the human colon adenocarcinoma cell line HT29 was determined. The results indicated a high adhesion and aggregation ability of L. rhamnosus PEN, which possessed specific surface proteins, had a unique fatty acid content, and did not synthesize EPS. Adherence of L. rhamnosus was dependent on specific interactions and was promoted by surface proteins (42–114 kDa) and specific fatty acids. Polysaccharides likely hindered bacterial adhesion and aggregation by masking protein receptors. This study provides information on the cell envelope constituents of lactobacilli that influence bacterial aggregation and adhesion to intestinal cells. This knowledge will help to understand better their specific contribution in commensal–host interactions and adaptation to this ecological niche.     

Effect of Cetylpyridinium Chloride on Microbial Adhesion to Hexadecane and Polystyrene

Microbial adhesion at the oil-water interface is a subject of both basic interest (e.g., as a technique for the measurement of hydrophobicity) and applied interest (e.g., for use in two-phase oil-water mouthwashes for the desorption of oral microorganisms). In general, surfactants inhibit microbial adhesion to oils and other hydrophobic surfaces. In the present study, we demonstrated that the cationic surfactant cetylpyridinium chloride (CPC) significantly enhanced microbial adhesion to hexadecane and various oils, as well as to the solid hydrophobic surface polystyrene. CPC increased adhesion to hexadecane of Escherichia coli, Candida albicans and Acinetobacter calcoaceticus MR-481 and of expectorated oral bacteria from near 0% to over 90%. The CPC concentration required for optimal enhancement of adhesion was a function of the initial cell density. This phenomenon was inhibited by high salt concentrations and, in the case of E. coli, by a low pH. CPC-pretreated cells were able to bind to hexadecane, but CPC-pretreated hexadecane was unable to bind untreated cells. Another cationic, surface-active antimicrobial agent, chlorhexidine gluconate, was similarly able to promote microbial adhesion to hexadecane. The results suggest that (i) CPC enhances microbial adhesion to hexadecane by binding via electrostatic interactions at the cell surface, thus diminishing surface charge and increasing cell surface hydrophobicity, and (ii) this phenomenon may have applications in oral formulations and in the use of hydrocarbon droplets as a support for cell immobilization.     

Influence of support material properties on the potential selection of Archaea during initial adhesion of a methanogenic consortium

In anaerobic wastewater treatment systems, the complex microbial biomass including Archaea and Bacteria can be retained as a biofilm attached to solid supports. The aim of this study was to evaluate the impact of specific properties of support material on early microbial adhesion. Seven different substrata are described in terms of topography and surface energy. Adhesion of a methanogenic consortium to these substrata was tested, the adhesion was quantified as a percentage of the surface area covered and the bacterial and archaeal community structures was assessed by molecular fingerprinting profiles (CE-SSCP). As expected, the overall adhesion on the supports was influenced mainly by total surface energy. Moreover, the adhered communities were different from the parent inocula, including the Archaea/Bacteria ratio. This could have a significant impact on the start-up of anaerobic digesters for which supports favoring Archaea adhesion, responsible for the limiting reaction of the process, should be preferred.     

Adhesion of Colletotrichum lindemuthianum Spores to Phaseolus vulgaris Hypocotyls and to Polystyrene

Adhesion of Colletotrichum lindemuthianum spores to Phaseolus vulgaris hypocotyls and to polystyrene was inhibited by the respiratory inhibitors sodium azide and antimycin A, indicating a requirement for metabolic activity in adhesion. Various commercial proteins and Tween 80 also reduced adhesion to both surfaces. Binding was enhanced by the presence of salts: sodium, potassium, calcium, and magnesium chlorides were equally effective. The removal of surface wax from hypocotyls by chloroform treatment greatly reduced their subsequent ability to bind spores. The results suggest a similar mechanism for spore adhesion to the plant surface and to polystyrene, involving purely physical surface properties rather than group-specific binding sites.     

The Electrostatic Nature of the Cell Surface of Candida albicans: A Role in Adhesion

Jones, L., and O'Shea, P. 1994. The electrostatic nature of the cell surface of Candida albicans: A role in adhesion. Experimental Mycology 18, 111-120. The yeast form of Candida albicans is subjected to particle electrophoresis in a variety of media, in order to determine whether the cell surface of the fungus conforms to a simple electrostatic system. It is found that C. albicans behaves essentially as a simple charged colloidal system. Similar measurements were performed with various glass surfaces in order to identify whether electrostatic interactions have any bearing on fungal adhesion. It was found that under all the circumstances studied, the fungi and glass were electronegative; the degree of adhesion was found to be affected by the magnitude of the coulombic repulsion. Significant adhesion still occurred, however, even when the coulombic repulsion was a maximum; this was taken to indicate that the fungal surface possesses other nonelectrostatic forces which are attractive. Both the electrostatic repulsive and the nonelectrostatic (presumably nonpolar) forces are considered to play a role in the adhesion of fungi to each other, to artificial surfaces such as glass, and presumably to other surfaces which occur in living systems.     

Surface Physicochemistry and Ionic Strength Affects eDNA’s Role in Bacterial Adhesion to Abiotic Surfaces

Extracellular DNA (eDNA) is an important structural component of biofilms formed by many bacteria, but few reports have focused on its role in initial cell adhesion. The aim of this study was to investigate the role of eDNA in bacterial adhesion to abiotic surfaces, and determine to which extent eDNA-mediated adhesion depends on the physicochemical properties of the surface and surrounding liquid. We investigated eDNA alteration of cell surface hydrophobicity and zeta potential, and subsequently quantified the effect of eDNA on the adhesion of Staphylococcus xylosus to glass surfaces functionalised with different chemistries resulting in variable hydrophobicity and charge. Cell adhesion experiments were carried out at three different ionic strengths. Removal of eDNA from S. xylosus cells by DNase treatment did not alter the zeta potential, but rendered the cells more hydrophilic. DNase treatment impaired adhesion of cells to glass surfaces, but the adhesive properties of S. xylosus were regained within 30 minutes if DNase was not continuously present, implying a continuous release of eDNA in the culture. Removal of eDNA lowered the adhesion of S. xylosus to all surfaces chemistries tested, but not at all ionic strengths. No effect was seen on glass surfaces and carboxyl-functionalised surfaces at high ionic strength, and a reverse effect occurred on amine-functionalised surfaces at low ionic strength. However, eDNA promoted adhesion of cells to hydrophobic surfaces irrespective of the ionic strength. The adhesive properties of eDNA in mediating initial adhesion of S. xylosus is thus highly versatile, but also dependent on the physicochemical properties of the surface and ionic strength of the surrounding medium.     

Effect of Milk Proteins on Adhesion of Bacteria to Stainless Steel Surfaces

Stainless steel coupons were treated with skim milk and subsequently challenged with individual bacterial suspensions of Staphylococcus aureus, Pseudomonas fragi, Escherichia coli, Listeria monocytogenes, and Serratia marcescens. The numbers of attached bacteria were determined by direct epifluorescence microscopy and compared with the attachment levels on clean stainless steel with two different surface finishes. Skim milk was found to reduce adhesion of S. aureus, L. monocytogenes, and S. marcescens. P. fragi and E. coli attached in very small numbers to the clear surfaces, making the effect of any adsorbed protein layer difficult to assess. Individual milk proteins α-casein, β-casein, κ-casein, and α-lactalbumin were also found to reduce the adhesion of S. aureus and L. monocytogenes. The adhesion of bacteria to samples treated with milk dilutions up to 0.001% was investigated. X-ray photoelectron spectroscopy was used to determine the proportion of nitrogen in the adsorbed films. Attached bacterial numbers were inversely related to the relative atomic percentage of nitrogen on the surface. A comparison of two types of stainless steel surface, a 2B and a no. 8 mirror finish, indicated that the difference in these levels of surface roughness did not greatly affect bacterial attachment, and reduction in adhesion to a milk-treated surface was still observed. Cross-linking of adsorbed proteins partially reversed the inhibition of bacterial attachment, indicating that protein chain mobility and steric exclusion may be important in this phenomenon.     

Bacillus cereus adhesion: Real time investigation of the effect on the chemistry of industrial stainless steel

The initial microorganism adhesion on substrate is an important step for the biofilm formation. The surface properties of the stainless steel and B. cereus were characterized by the sessile drop technique. Moreover, the physicochemical properties of surface adhesion and the impact of bio adhesion to the stainless steel were determined at different time of contact (2, 4, 7, 9 and 24 h). The results showed that the strain was hydrophilic (Giwi = 3.37 mJ/m²), whereas the substratum has hydrophobic character (Giwi = ?57.6 mJ/m²). Stainless steel surface presents a weak electron-donor character (γ^? = 4.1 mJ/m²) conversely to B. cereus that presents an important parameter (γ^? = 31.6 mJ/m²). The bio adhesion was investigated at different time of contact. The data analysis after 2 h, confirmed the adhesion of B. cereus with an amount of 10 cfu/cm² which increased to 1.210⁴ cfu/cm² after 24 h. Interestingly, despite the difference of hydropohbicity, the interaction between B. cereus and substratum was favored by the thermodynamic aspect of adhesion (ΔG_adhesion < 0). Interestingly, the study of the effect of B. cereus adhesion on the stainless steel has revealed that, the substratum becomes hydrophilic (θ° = 41.3, ΔGiwi = 39.6 mJ/m²) and highly electron donor (Γ^? = 52.9 mJ/m²) after 2 h of bio adhesion.     

BopA Does Not Have a Major Role in the Adhesion of Bifidobacterium bifidum to Intestinal Epithelial Cells,Extracellular Matrix Proteins,and Mucus

The ability of bifidobacteria to adhere to the intestine of the human host is considered to be important for efficient colonization and achieving probiotic effects. Bifidobacterium bifidum strains DSM20456 and MIMBb75 adhere well to the human intestinal cell lines Caco-2 and HT-29. The surface lipoprotein BopA was previously described to be involved in mediating adherence of B. bifidum to epithelial cells, but thioacylated, purified BopA inhibited the adhesion of B. bifidum to epithelial cells in competitive adhesion assays only at very high concentrations, indicating an unspecific effect. In this study, the role of BopA in the adhesion of B. bifidum was readdressed. The gene encoding BopA was cloned and expressed without its lipobox and hydrophobic signal peptide in Escherichia coli, and an antiserum against the recombinant BopA was produced. The antiserum was used to demonstrate the abundant localization of BopA on the cell surface of B. bifidum. However, blocking of B. bifidum BopA with specific antiserum did not reduce adhesion of bacteria to epithelial cell lines, arguing that BopA is not an adhesin. Also, adhesion of B. bifidum to human colonic mucin and fibronectin was found to be BopA independent. The recombinant BopA bound only moderately to human epithelial cells and colonic mucus, and it failed to bind to fibronectin. Thus, our results contrast the earlier findings on the major role of BopA in adhesion, indicating that the strong adhesion of B. bifidum to epithelial cell lines is BopA independent.     

Shear-stabilized rolling behavior of E. coli examined with simulations

Escherichia coli exhibit both shear-stabilized rolling and a transition to stationary adhesion while adhering in fluid flow. Understanding the mechanism by which this shear-enhanced adhesion occurs is an important step in understanding bacterial pathogenesis. In this work, simulations are used to investigate the relative contributions of fimbrial deformation and bond transitions to the rolling and stationary adhesion of E. coli. Each E. coli body is surrounded by many long, thin fimbriae terminating in a single FimH receptor that is capable of forming a catch bond with mannose. As simulated cells progress along a mannosylated surface under flow, the fimbriae bend and buckle as they interact with the surface, and FimH-mannose bonds form and break according to a two-state, allosteric catch-bond model. In simulations, shear-stabilized rolling resulted from an increase in the low-affinity bond number due to increased fimbrial deformation with shear. Catch-bond formation did not occur during cell rolling, but instead led to the transition to stationary adhesion. In contrast, in leukocyte and platelet systems, catch bonds appear to be involved in the stabilization of rolling, and integrin activation is required for stationary adhesion.     

Adhesion of Bifidobacteria to Granular Starch and Its Implications in Probiotic Technologies

Adhesion of 19 Bifidobacterium strains to native maize, potato, oat, and barley starch granules was examined to investigate links between adhesion and substrate utilization and to determine if adhesion to starch could be exploited in probiotic food technologies. Starch adhesion was not characteristic of all the bifidobacteria tested. Adherent bacteria bound similarly to the different types of starch, and the binding capacity of the starch (number of bacteria per gram) correlated to the surface area of the granules. Highly adherent strains were able to hydrolyze the granular starches, but not all amylolytic strains were adherent, indicating that starch adhesion is not a prerequisite for efficient substrate utilization for all bifidobacteria. Adhesion was mediated by a cell surface protein(s). For the model organisms tested (Bifidobacterium adolescentis VTT E-001561 and Bifidobacterium pseudolongum ATCC 25526), adhesion appeared to be specific for α-1,4-linked glucose sugars, since adhesion was inhibited by maltose, maltodextrin, amylose, and soluble starch but not by trehalose, cellobiose, or lactose. In an in vitro gastric model, adhesion was inhibited both by the action of protease and at pH values of ≤3. Adhesion was not affected by bile, but the binding capacity of the starch was reduced by exposure to pancreatin. It may be possible to exploit adhesion of probiotic bifidobacteria to starch granules in microencapsulation technology and for synbiotic food applications.     

Acanthamoeba culbertsoni: Analysis of amoebic adhesion and invasion on extracellular matrix components collagen I and laminin-1

Acanthamoeba are free-living amoebae found in most environments that can cause brain and corneal infections. To infect humans, these pathogens must interact with host cells and the extracellular matrix (ECM). In order to define the mode by which amoebae recognize ECM components and process this recognition, we analyzed Acanthamoeba culbertsoni attachment and invasion, respectively, on collagen I and laminin-1 and on tridimensional collagen I and matrigel matrices. We determined that amoebae surface proteins are involved in adhesion, that exogenous sugars can decrease adhesion and invasion, and that adhesion and invasion are dependent on microfilament reorganization. In addition, we determined the role of serine- and metallo-proteases on invasion and found that adhesion was blocked when amoebae were treated with a metallo-protease inhibitor. Collectively, these results suggest that adhesion and invasion are protease- and microfilament-dependent events in which amoebic surface proteins play a pivotal role.