Bacterial adhesion at synthetic surfaces.

A systematic investigation into the effect of surface chemistry on bacterial adhesion was carried out. In particular, a number of physicochemical factors important in defining the surface at the molecular level were assessed for their effect on the adhesion of Listeria monocytogenes, Salmonella typhimurium, Staphylococcus aureus, and Escherichia coli. The primary experiments involved the grafting of groups varying in hydrophilicity, hydrophobicity, chain length, and chemical functionality onto glass substrates such that the surfaces were homogeneous and densely packed with functional groups. All of the surfaces were found to be chemically well defined, and their measured surface energies varied from 15 to 41 mJ. m(-2). Protein adsorption experiments were performed with (3)H-labelled bovine serum albumin and cytochrome c prior to bacterial attachment studies. Hydrophilic uncharged surfaces showed the greatest resistance to protein adsorption; however, our studies also showed that the effectiveness of poly(ethyleneoxide) (PEO) polymers was not simply a result of its hydrophilicity and molecular weight alone. The adsorption of the two proteins approximately correlated with short-term cell adhesion, and bacterial attachment for L. monocytogenes and E. coli also correlated with the chemistry of the underlying substrate. However, for S. aureus and S. typhimurium a different pattern of attachment occurred, suggesting a dissimilar mechanism of cell attachment, although high-molecular-weight PEO was still the least-cell-adsorbing surface. The implications of this for in vivo attachment of cells suggest that hydrophilic passivating groups may be the best method for preventing cell adsorption to synthetic substrates provided they can be grafted uniformly and in sufficient density at the surface.     

The behavior of platelets at foreign surfaces

Many conditions affect the interaction of platelets with foreign surfaces, including the type of surface, modifications of the surface, conditions of blood flow, the adsorbed layer of plasma proteins, changes in this protein layer with time, and the animal species in which experiments are done. Platelets probably never adhere directly to a foreign surface in vivo, because upon exposure of the surface to blood, plasma proteins, principally fibrinogen, are adsorbed almost immediately. When platelets adhere to such a surface and spread on it, they are activated in much the same way as when they are exposed to a strong aggregating and release-inducing agent, but in contrast to aggregation caused by some agonists, adhesion is not dependent on the formation of TXA2 or the release of ADP. It does appear to depend on external Ca2+. Much less is known about the initial adhesion reaction than about platelet aggregation (thrombus formation) on the adherent platelets, although the morphological changes resulting from adhesion have been described. It is surmised that the metabolic and cytoskeletal changes upon adhesion are similar to those that are involved in the response of platelets to other activating agents. The consequences of adhesion include the formation of thrombi and thromboemboli, thrombocytopenia, reduced platelet survival, reduced platelet function in response to hemostatic stimuli, and the appearance in the circulation of products released or formed by activated platelets. Many efforts are being made to develop surfaces and to set up conditions that will minimize platelet adhesion, but it has not yet been possible to find a foreign surface that has and can maintain the nonthrombogenic characteristics of the normal endothelium.     

Bacterial interplay at intestinal mucosal surfaces: implications for vaccine development

The discovery of 'molecular syringes' in several important gastrointestinal pathogens including Escherichia coli, Salmonella, Shigella and Yersinia, together with a better understanding of M cells and the mucosal immune system, has advanced our appreciation of multistage microorganism-host cell interactions. Recent studies suggest that these molecular strategies could be adapted for the development of modular mucosal vaccines.     

Bacterial migration along solid surfaces.

An in vitro system was developed to study the migration of uropathogenic Escherichia coli strains. In this system an aqueous agar gel is placed against a solid surface, allowing the bacteria to migrate along the gel/solid surface interface. Bacterial strains as well as solid surfaces were characterized by means of water contact angle and zeta potential measurements. When glass was used as the solid surface, significantly different migration times for the strains investigated were observed. Relationships among the observed migration times of six strains, their contact angles, and their zeta potentials were found. Relatively hydrophobic strains exhibited migration times shorter than those of hydrophilic strains. For highly negatively charged strains shorter migration times were found than were found for less negatively charged strains. When the fastest-migrating strain with respect to glass was allowed to migrate along solid surfaces differing in hydrophobicity and charge, no differences in migration times were found. Our findings indicate that strategies to prevent catheter-associated bacteriuria should be based on inhibition of bacterial growth rather than on modifying the physicochemical character of the catheter surface.     

Bacterial migration along solid surfaces.

An in vitro system was developed to study the migration of uropathogenic Escherichia coli strains. In this system an aqueous agar gel is placed against a solid surface, allowing the bacteria to migrate along the gel/solid surface interface. Bacterial strains as well as solid surfaces were characterized by means of water contact angle and zeta potential measurements. When glass was used as the solid surface, significantly different migration times for the strains investigated were observed. Relationships among the observed migration times of six strains, their contact angles, and their zeta potentials were found. Relatively hydrophobic strains exhibited migration times shorter than those of hydrophilic strains. For highly negatively charged strains shorter migration times were found than were found for less negatively charged strains. When the fastest-migrating strain with respect to glass was allowed to migrate along solid surfaces differing in hydrophobicity and charge, no differences in migration times were found. Our findings indicate that strategies to prevent catheter-associated bacteriuria should be based on inhibition of bacterial growth rather than on modifying the physicochemical character of the catheter surface.     

Bacterial attachment on optical fibre surfaces

Optical fibres have received considerable attention as high-density sensor arrays suitable for both in vitro and in vivo measurements of biomolecules and biological processes in living organisms and/or nano-environments. The fibre surface was chemically modified by exposure to a selective etchant that preferentially erodes the fibre cores relative to the surrounding cladding material, thus producing a regular pattern of cylindrical wells of approximately 2.5 μm in diameter and 2.5 μm deep. The surface hydrophobicity of the etched and non-etched optical fibres was analysed using the sessile pico-drop method. The surface topography was characterised by atomic force microscopy (AFM), while the surface chemistry was probed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Six taxonomically different bacterial strains showed a consistent preference for attachment to the nano-scale smoother (R _q = 273 nm), non-etched fibre surfaces (water contact angle, θ = 106° ± 4°). In comparison, the surfaces of the etched optical fibres (water contact angle, θ = 96° ± 10°) were not found to be amenable to bacterial attachment. Bacterial attachment on the non-etched optical fibre substrata varied among different strains.     

Bacterial adsorption to thermoresponsive polymer surfaces

The ability of microorganisms to `recognise' a change in the hydrophobicity/hydrophilicity balance of the surface was demonstrated using thermoresponsive poly(N-isopropylacrylamide) co-polymers with different Lower Critical Solution Temperatures. The polymers were grafted onto hydrolysed glass under well controlled conditions and the adhesion was followed using ¹³C-labelled Listeria monocytogenes. Attachment of the bacteria was found to be directly affected by the polymer transition from a hydrophilic to a hydrophobic state but by less than one order of magnitude.     

Bacterial leaching patterns on pyrite crystal surfaces

Selected pyrite crystals were placed as a bacterial energy source into stationary cultures of Thiobacillus ferroxidans. Scanning electron microscope studies performed after a period of 2 years on these crystals revealed bacterial etching pits in characteristic patterns; they include pit arrangements in loose statistical disorder, in pairs, in clusters, and most remarkably in pearl-string-like chains. It has previously been confirmed that the chemical processes of bacterial leaching occur mainly in the region of contact between bacteria and the sulfide surface. The evidence presented in this experiment strongly suggests that the observed bacterial distributions are critically dependent on crystal structure and on deviations in the crystal order (fracture lines, dislocations) of the leachable substrate.     

Bacterial killing by dry metallic copper surfaces

Metallic copper surfaces rapidly and efficiently kill bacteria. Cells exposed to copper surfaces accumulated large amounts of copper ions, and this copper uptake was faster from dry copper than from moist copper. Cells suffered extensive membrane damage within minutes of exposure to dry copper. Further, cells removed from copper showed loss of cell integrity. Acute contact with metallic copper surfaces did not result in increased mutation rates or DNA lesions. These findings are important first steps for revealing the molecular sensitive targets in cells lethally challenged by exposure to copper surfaces and provide a scientific explanation for the use of copper surfaces as antimicrobial agents for supporting public hygiene.     

Adsorption behavior of a human monoclonal antibody at hydrophilic and hydrophobic surfaces

One aspiration for the formulation of human monoclonal antibodies (mAb) is to reach high solution concentrations without compromising stability. Protein surface activity leading to instability is well known, but our understanding of mAb adsorption to the solid-liquid interface in relevant pH and surfactant conditions is incomplete. To investigate these conditions, we used total internal reflection fluorescence (TIRF) and neutron reflectometry (NR). The mAb tested (“mAb-1”) showed highest surface loading to silica at pH 7.4 (~12 mg/m²), with lower surface loading at pH 5.5 (~5.5 mg/m², further from its pI of 8.99) and to hydrophobized silica (~2 mg/m²). The extent of desorption of mAb-1 from silica or hydrophobized silica was related to the relative affinity of polysorbate 20 or 80 for the same surface. mAb-1 adsorbed to silica on co-injection with polysorbate (above its critical micelle concentration) and also to silica pre-coated with polysorbate. A bilayer model was developed from NR data for mAb-1 at concentrations of 50–5000 mg/L, pH 5.5, and 50–2000 mg/L, pH 7.4. The inner mAb-1 layer was adsorbed to the SiO₂ surface at near saturation with an end-on” orientation, while the outer mAb-1 layer was sparse and molecules had a “side-on” orientation. A non-uniform triple layer was observed at 5000 mg/L, pH 7.4, suggesting mAb-1 adsorbed to the SiO₂ surface as oligomers at this concentration and pH. mAb-1 adsorbed as a sparse monolayer to hydrophobized silica, with a layer thickness increasing with bulk concentration - suggesting a near end-on orientation without observable relaxation-unfolding.     

细菌的群体性行为与耐药

随着抗生素的广泛使用,细菌耐药已经成为一个严重的问题。细菌耐药是一个复杂的过程,涉及宿主、细菌与环境等几个既相互独立又相互作用的因素。很久以来,人们认为细菌以个体为单位进行各种活动,直到发现细菌相互之间也存在联系,才意识到细菌群体对其个体生存的重要性。目前将细菌作为一个群体来研究其耐药行为与机制的研究越来越多,特别是细菌生物膜与细菌程序性死亡两方面受到极大重视。本文综述了细菌生物膜、细菌程序性死亡与耐药相关机制的研究进展。     

Bacterial desorption from food container and food processing surfaces

The desorption ofStaphylococcus aureus, Acinetobacter calcoaceticus, and a coryneform from the surfaces of materials used for manufacturing food containers (glass, tin plate, and polypropylene) or postprocess canning factory conveyor belts (stainless steel and nylon) was investigated. The effect of time, pH, temperature, and adsorbed organic layers on desorption was studied.S. aureus did not detach from the substrata at any pH investigated (between pH 5 and 9).A. calcoaceticus and the coryneform in some cases detached, depending upon pH and substratum composition. The degree of bacterial detachment from the substrata was not related to bacterial respiration at experimental pH values. Bacterial desorption was not affected by temperature (4–30°C) nor by an adsorbed layer of peptone and yeast extract on the substrata. The results indicate that bacterial desorption, hence bacterial removal during cleaning or their transfer via liquids flowing over colonized surfaces, is likely to vary with the surface composition and the bacterial species colonizing the surfaces.     

Bacterial deposition on and detachment from surfaces in turbulent flow

A number of experimental studies on deposition and detachment of bacterial cells of Pseudomonas sp. was performed in an inclined plate apparatus 2.3 m long. In each run, ca. 10(8)cells were introduced into a layer of flowing water at Reynolds numbers of ca. 1000 and 1300. After a preset time, the flow was stopped and the position of attached cells measured. Spatial pattern of attached cells was initially aggregative and remained so for lower flow rates. For higher flow rates the pattern tended towards randomness, perhaps as a result of cell detachment. Overall sticking efficiency of cells was very small (ca. 10(-5)).     

Bacterial Adhesion at Synthetic Surfaces

A systematic investigation into the effect of surface chemistry on bacterial adhesion was carried out. In particular, a number of physicochemical factors important in defining the surface at the molecular level were assessed for their effect on the adhesion of Listeria monocytogenes, Salmonella typhimurium, Staphylococcus aureus, and Escherichia coli. The primary experiments involved the grafting of groups varying in hydrophilicity, hydrophobicity, chain length, and chemical functionality onto glass substrates such that the surfaces were homogeneous and densely packed with functional groups. All of the surfaces were found to be chemically well defined, and their measured surface energies varied from 15 to 41 mJ · m⁻². Protein adsorption experiments were performed with ³H-labelled bovine serum albumin and cytochrome c prior to bacterial attachment studies. Hydrophilic uncharged surfaces showed the greatest resistance to protein adsorption; however, our studies also showed that the effectiveness of poly(ethyleneoxide) (PEO) polymers was not simply a result of its hydrophilicity and molecular weight alone. The adsorption of the two proteins approximately correlated with short-term cell adhesion, and bacterial attachment for L. monocytogenes and E. coli also correlated with the chemistry of the underlying substrate. However, for S. aureus and S. typhimurium a different pattern of attachment occurred, suggesting a dissimilar mechanism of cell attachment, although high-molecular-weight PEO was still the least-cell-adsorbing surface. The implications of this for in vivo attachment of cells suggest that hydrophilic passivating groups may be the best method for preventing cell adsorption to synthetic substrates provided they can be grafted uniformly and in sufficient density at the surface.     

Bacterial translational control at atomic resolution

Translational regulation allows rapid adaptation of protein synthesis to environmental conditions. In prokaryotes, the synthesis of many RNA-binding proteins is regulated by a translational feedback mechanism involving a competition between their natural substrate and their binding site on mRNA, which are often thought to resemble each other. This article describes the case of threonyl-tRNA synthetase, which represses the translation of its own mRNA. Recent data provide the first opportunity to describe at the atomic level both the extent and the limit of mimicry between the way this enzyme recognizes tRNA(Thr) and its regulatory site in mRNA. The data also give some clues about how the binding of the synthetase to its mRNA inhibits translation.     

Bacterial chitin utilization at halophilic conditions

Chitin is a dominant structural polymer produced in large amounts by brine shrimp Artemia in hypersaline lakes. Microbiological analysis of chitin utilization as a growth substrate in hypersaline chloride–sulfate lakes in the south Kulunda Steppe (Altai, Russia) revealed two groups of bacteria able to grow on chitin at moderate salinity. Under aerobic conditions, an enrichment culture was obtained at 2 M NaCl. Further purification resulted in the isolation of strains HCh1 and strain HCh2, identified as representatives of the genera Saccharospirillum and Arhodomonas (both in the Gammaproteobacteria). The chitin-utilizing potential has not been previously recognized in these genera. The Saccharospirillum sp. strain HCh1 grew on chitin within the salinity range from 0.5 to 3.25 M NaCl (optimum at 1 M), while Arhodomonas sp. strain HCh2 grew up to 2.5 M NaCl but had a higher salt optimum at 1.5 M. Anaerobic enrichments grew with chitin at 2 and 4 M NaCl, but growth in the latter was extremely slow and the culture eventually lost viability. The enrichment at 2 M NaCl resulted in the isolation of strain HCh-An1, identified as a distant new species of the genus Orenia in the clostridial order Halanaerobiales. It was able to grow on chitin within a salinity range from 1.0 to 2.5 M NaCl (optimum at 1.5 M). The strain is proposed as a new species of the genus Orenia—O. chitinitropha.     

Bacterial gene expression at low temperatures

Under suboptimal environmental conditions such as low temperatures, many bacteria have an extended lag phase, altered cell structures, and composition such as a less fluid (more rigid) and leaky cytoplasmic membrane. As a result, cells may die, enter into a starvation mode of metabolism or a physiologically viable but non-culturable (VBNC) state. In the latter state, the amount of gene expression per cell is virtually undetectable. In this article, gene expression under (suboptimal) low temperature conditions in non-psychrophilic environmental bacteria is examined. The pros and cons of some of the molecular methodologies for gene expression analysis are also discussed.