Shewanella putrefaciens adhesion and biofilm formation on food processing surfaces

Laboratory model systems were developed for studying Shewanella putrefaciens adhesion and biofilm formation under batch and flow conditions. S. putrefaciens plays a major role in food spoilage and may cause microbially induced corrosion on steel surfaces. S. putrefaciens bacteria suspended in buffer adhered readily to stainless steel surfaces. Maximum numbers of adherent bacteria per square centimeter were reached in 8 h at 25 degrees C and reflected the cell density in suspension. Numbers of adhering bacteria from a suspension containing 10(8) CFU/ml were much lower in a laminar flow system (modified Robbins device) (reaching 10(2) CFU/cm(2)) than in a batch system (reaching 10(7) CFU/cm(2)), and maximum numbers were reached after 24 h. When nutrients were supplied, S. putrefaciens grew in biofilms with layers of bacteria. The rate of biofilm formation and the thickness of the film were not dependent on the availability of carbohydrate (lactate or glucose) or on iron starvation. The number of S. putrefaciens bacteria on the surface was partly influenced by the presence of other bacteria (Pseudomonas fluorescens) which reduced the numbers of S. putrefaciens bacteria in the biofilm. Numbers of bacteria on the surface must be quantified to evaluate the influence of environmental factors on adhesion and biofilm formation. We used a combination of fluorescence microscopy (4',6'-diamidino-2-phenylindole staining and in situ hybridization, for mixed-culture studies), ultrasonic removal of bacteria from surfaces, and indirect conductometry and found this combination sufficient to quantify bacteria on surfaces.     

Biofuels from food processing wastes

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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 behavior at surfaces

Population level studies demonstrate that bacterial colonization of surfaces and subsequent biofilm architecture are controlled by a variety of factors that include the hydrodynamics, surface chemistry and genotype of the cell. New molecular tools now extend our ability to investigate among bacterial cells within a surface-associated population subtle phenotypic differences that do not involve changes in genotype. Such resolution has led to new discoveries in relationships between bacterial cells and their environment.     

Target coatings and desorption surfaces in biomolecular MALDI-MS

MALDI-MS is an extremely flexible technique and can be synergistically used in conjunction with established bioanalytical methods such as PAGE or SPR. To that end, slight modifications on the sample target plate may be necessary. Those can involve the use of hydrophobic coatings for improved sample deposition and desalting or that of sensor surfaces for on-target bioaffinity experiments. In particular the latter have evolved considerably over the past years. Surface coatings using polysaccharide or polycarboxylate hydrogels were adopted from unrelated techniques and they proved very suitable for bioaffinity MS. The developments concerning target modification and derivatization are reviewed.     

Polysaccharides and food processing

The rôle of polysaccharides during processing and for the quality of foods is discussed. Starch is the most important energy source for man. Most other polysaccharides are not metabolized for energy, but play an important rôle as dietary fibres. Pectins, alginates, carrageenans, and galactomannans are discussed as functional food additives in relation to their structure and their rheological behaviour, stability and interactions. Endogenous polysaccharides of fruits and vegetables and in products derived from them are responsible for such phenomena as texture (changes), press yields, ease of filtration and clarification, cloud stability, and mouth feel. To achieve desirable properties, the action of endogenous enzymes on polysaccharides must be inactivated and/or exogenous enzymes added as processing aids. This is also true for overcoming haze phenomena in clear juices or to break down undesirable microbial polysaccharides. Dough properties for bread baking can be improved by enzymic breakdown of a restrictive pentoglycan network. Network formation may come about by oxidative coupling of phenol rings of ferulic acid bound to hemicelluloses by ester links. Gels may be made by inducing oxidative coupling in natural or synthetic systems. Stagnation in development of new polysaccharide food additives is ascribed to difficulties in obtaining government approval for food use.     

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 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.     

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.     

细菌生物被膜与食品生物危害

食源性病原菌生物被膜是威胁食品安全的一个重大隐患。生物被膜一旦在食品加工过程中形成,易引起相当严重的交叉污染和加工后污染,产生极大危害,从而导致一系列严重的健康问题。本文就食源性病原菌生物被膜的分布、形成机制以及防治措施进行了综述。     

Recent trends in bioethanol production from food processing byproducts

The widespread use of corn starch and sugarcane as sources of sugar for the production of ethanol via fermentation may negatively impact the use of farmland for production of food. Thus, alternative sources of fermentable sugars, particularly from lignocellulosic sources, have been extensively investigated. Another source of fermentable sugars with substantial potential for ethanol production is the waste from the food growing and processing industry. Reviewed here is the use of waste from potato processing, molasses from processing of sugar beets into sugar, whey from cheese production, byproducts of rice and coffee bean processing, and other food processing wastes as sugar sources for fermentation to ethanol. Specific topics discussed include the organisms used for fermentation, strategies, such as co-culturing and cell immobilization, used to improve the fermentation process, and the use of genetic engineering to improve the performance of ethanol producing fermenters.     

Bacterial modulation of antigen processing and presentation

This review examines the mechanisms by which bacteria influence the antigenic processing of endogenous and exogenous antigens presented by class I, class II, and nonclassical MHC molecules. Consequent effects on presentation of bacterial antigens, the ability of bacteria to evade host defences, and the potential induction of autoimmunity are discussed.     

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.     

The effect of physical and microbiological factors on food container leakage

The effect of physical and microbiological factors on food container leakage was investigated in a container leakage model system (CLMS). The leakage of Acinetobacter calcoaceticus, Staphylococcus sp., Pseudomonas sp., Bacillus sp., a coryneform, Staph. aureus, and two biotest organisms (Enterobacter cloacae NC1B 8151 and Ent. aerogenes MB31) was studied. The rate of bacterial leakage (log10 cells/channel/s) was greater in the presence of a partial vacuum of 51-305 mm Hg than at atmospheric pressure. Fluid flow (ml) through leakage channels was increased by the application of vacuum. Leakage varied with vacuum, bacterial morphology, cell concentration, leakage channel size (0.78-120 micron 2) and channel shape (straight or convoluted). The number of leaked cells was not proportional to vacuum or channel size. The effect of channel shape varied with bacterial species. Increased container medium viscosity decreased bacterial leakage. Fluid flow through leakage channels was generally reduced by the most viscous solution. Cells from biofilms and monolayers of Ac. calcoaceticus or Staph. aureus attached to nylon (Hyfax) or stainless steel surfaces underwent leakage. Mixed bacterial populations had characteristic leakage rates against vacuum different from the leakage pattern of individual species in the population. The composition of the leaked population was different from the original inoculum. The results indicated that container leakage is a complex process involving a range of interdependent factors.     

Discontinuous formation and desorption of clusters during particles adsorption at surfaces

A theoretical model was derived to describe the discontinuous formation and desorption of clusters during particle adsorption at surfaces. Two steps were investigated: (1) time-dependent adsorption, where we found that the initial slope and the limiting magnitude of an adsorption isotherm depend on the clusters' distribution. A higher magnitude of both the adsorption and desorption rates appear to contract the time scale and hence increase the initial slope. Decreasing the geometrical parameter, q, which represents the shape of an adsorbed cluster, enhances the growth of large clusters on the surface. (2) A concentration dependence model shows that the number of adsorbed molecules increases with increases in the value of n (nucleation capacity). Furthermore, higher rates of adsorption provide steeper initial slopes (higher affinity of, molecules to surface). Decreasing q from 2 to 1, i.e. from a circular to a linear cluster formation, slightly decreases the magnitude of the isotherms.