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The main `cement' for all these cells and products is the mixture of polysaccharides secreted by the cells established within the biofilm.
The major component in the biofilm matrix is water - up to 97% (Zhang et al.,1998), and the characteristics of the solvent are determined by the solutes dissolved in it. The exact structure of any biofilm is probably a unique feature of the environment in which it develops.
Stoodley et al. (1999a), nutritional and physical conditions greatly affect the nature of laboratory biofilms and this is equally true for other types. Wimpenny & Colasanti (1997) have also suggested that biofilm structureis largely determined by the concentration of substrate.
They further postulated that such differences also validate at least three conceptual models of biofilms- heterogeneous mosaics, structures penetrated by water channels, and dense confluent biofilms.
Any study of biofilms must accept that biofilms may develop in an enormous number of environments, and that the structural intricacies of any single biofilm formed under any specific set of parameters may well be unique to that single environment and microflora.
The enormous number of microbial species capable of forming biofilms or interacting with others to do so, together with the very great range of polysaccharides produced, gives rise to an infinite number of permutations.
Most biofilms are composed of mixtures of micro-organisms. This adds to the interspecies and intraspecies interactions and to the general complexity of the macromolecular mixture present.
The exopolysaccharides (EPS) synthesized by microbial cells vary greatly in their composition and hence in their chemical and physical properties.
In several preparations, the polysaccharides have been visualized as fine strands attached to the bacterial cell surface and forming a complex network surrounding the cell. Mayer et al. (1999) suggested that electrostatic and hydrogen bonds are the dominant forces involved.
Ionic interactions may be involved, but more subtle chain-chain complex formation in which one macromolecule ` fits ' into the other may result in either floc formation or networks which are very poorly soluble in aqueous solvents.
Another result may be the formation of strong or weak gels. The polysaccharides can thus form various types of structures within a biofilm. However, in biofilms thepolysaccharides do not exist alone but may interact with a wide range of other molecular species, including lectins, proteins, lipids etc., as well as with other polysaccharides.
The resultant tertiary structure comprises a network of polysaccharide and other macromolecules, in which cells and cell products are also trapped.
The EPS present in biofilms almost certainly resemble closely the corresponding polymers synthesized by planktonic cells.
Those bacteria capable of forming several different polysaccharides may produce more of one found in lower amounts in planktonic cultures ; this again is probably part of a stress response.
One result of this effect has been the report of variations in polysaccharide composition, almost certainly due to the varying proportions of the different polysaccharides synthesized within the biofilm. This is also true of biofilms containing a mixture of microbial species. In these, it must be remembered that the relative amounts of different polysaccharides and the proportions of the microbial cells present will depend greatly on the physiological state of the biofilm.
It is also quite possible that within extensive biofilms, different subpopulations might have miscellaneous micro-environments leading to production of different mixtures of polysaccharides
The slow bacterial growth observed in most biofilms would also be expected to enhance EPS production.
However, when the bacteria are components of mixed biofilms, the presence of one species producing copious amounts of EPS may enhance the stability of other cell types even if they do not themselves synthesize EPS. Such stabilizing effects were considered by James et al. (1995) to be commensal interactions.
As pointed out by Skillman et al. (1999), the proportions of different EPS in mixed biofilms do not necessarily reflect the proportions of the cells present, nor do the EPS contribute equally to the structure and properties of the resulting biofilms.
In most cases, the presence of multivalent cations such as Ca2+ will lead to more extensive formation of ordered helices than monovalent ions, although some polysaccharides resemble kappa carrageenan and reveal aggregates of double helices in the presence of K+.
It is probable that many of the EPS in biofilms bind lesser quantities whilst some, like bacterial cellulose, mutan or curdlan, manage to exclude most water from their tertiary structure. The EPS will also contribute to the mechanical stability of the biofilms (Mayer et al., 1999), enabling them to withstand considerable shear forces.
In some polymers, the interaction with ions may yield relatively rigid gels which are less readily deformed by shear, thus producing amuch more stable biofilm.
They thus confer very different properties on the matrices in which they are found and account for the wide differences in properties found in different biofilms.
The algal polysaccharides readily form rigid, non-deformable gels due to the highly specific interaction with either Ca2+ or Sr2+, a property which is widely used in biotechnology for the immobilization of cells and enzymes.
The bacterial polysaccharides are acetylated and the acetyl groups strongly inhibit the interaction between polymer chains and cations and resultant gel formation.
The resultant polysaccharides yield highly viscous aqueous solutions with viscoelastic properties.
Those EPS molecules, which are effectively in solution, may well dissolve with dilution, thus accounting in part for the observed `sloughing off' of biofilm material. It has to be remembered that enzymes will also contribute to this (Boyd&Chakrabarty, 1994).
Another aspect, which has received relatively little study, is the possibility of interaction of EPS with proteins and other excreted or surface-associated macromolecules. Either association or segregation may occur.
As yet, relatively little is known about the interactions which occur between biofilm EPS and enzymes (Sutherland, 1999b). Whilst proteases would certainly affect those proteins which interact with EPS within biofilms, polysaccharases and polysaccharide lyases can have a much greater effect.
In experimental systems, it is clear that the effect of any enzyme degrading any one EPS will depend on the other EPS and microbial cells present in the biofilm treatment with either the polysaccharase or a protease reduced the adhesion of these bacteria to a monolayer of Klebsiella pneumoniae cells.
This indicated roles for both the polysaccharide and proteins in the adhesion process and suggests that considerable differences can be expected when different combinations of microbial species are examined.
Some bacteria secrete esterases with wide specificity ; these can remove acyl groups from bacterial polymers as well as from other esters (Cui et al., 1999). Such enzymes could alter the physical properties of a biofilm structure, either locally or to a greater extent.
Many bacteria are capable of synthesizing and excreting surfactants, some of which, such as emulsan, resemble lipopolysaccharides (LPS), whilst rhamnolipids are products of Pseudomonas spp.
In either case, the outermost layer of the EPS may lose water and harden to form an effective in providing protection against further desiccation. EPS may offer little protection against bacteriophage or bacteriocins when these are present in appreciable concentrations.
The release of more phage particles and enzyme activity on completion of the lytic cycle will further damage or remove the biofilm, as was demonstrated in biofilms of enteric species by Hughes et al.
As any biofilm is unlikely to comprise a single type of EPS, the effect of enzyme action will depend on whether its substrate plays a major role in maintaining the biofilm structure. Thus, Skillman et al. (1999) observed that in biofilms composed of mixed enteric species, hydrolysis of one EPS caused greater destruction of the biofilm than did removal of the other.
This would indicate that, as in cell walls, certain polymers may provide a fairly rigid scaffolding onto or into which other polymers attach to fill the interstices.
The environments in which biofilms are found vary greatly.
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From the American Society of Microbiology's 2007 Biofilm Conference:
Visualization of Antimicrobial Action Against Biofilms.
P. S. Stewart; Montana State University, Bozeman, MT
The action of antimicrobial agents against bacterial biofilms of Staphylococcus epidermidis or a mixture of three oral species was visualized by a time-lapse microscopy technique allowing spatial and temporal patterns to be discerned non-invasively.
Biofilms were grown in a flow cell and then prestained with Calcein-AM. This fluorogenic esterase substrate loads cells with an unbound green fluorescent dye that remains trapped inside the cell as long as the cell membrane is intact.
If membrane integrity is compromised, for example by an antimicrobial agent, the dye leaks out and the cell becomes dark.
Using confocal scanning laser microscopy, the action of glutaraldehyde,chlorine, a quaternary ammonium biocide, chlorhexidine, and an antimicrobial peptide, nisin, were observed under flow conditions.
Each antimicrobial exhibited a distinct spatio-temporal pattern of action in biofilm clusters. During chlorine treatment,fluorescence loss occurred in a thin layer at the periphery of the biofilm which progressed toward the center while the clusters were simultaneously eroded.
This pattern could be attributed to limited penetration of chlorine due to a reaction-diffusion interaction.
Treatment with the quaternary ammonium compound resulted in biphasic loss of fluorescence in biofilm clusters.
A fraction of the cell population mostly located in the interior of the clusters remained bright for a longer time.
This pattern suggests two populations within the biofilm; one that is rapidly permeabilized by the agent and a second that is much less susceptible.
Glutaraldehyde treatment did not cause any loss of fluorescence, suggesting that this biocide does not cause cellular envelope permeabilization.
Treatment with the antimicrobial peptide, nisin, resulted in rapid, uniform fluorescence loss within the biofilm clusters.
The rapid fluorescence loss during this treatment implies that nisin penetrated quickly and affected the membrane integrity of all the cells within the biofilm.
Data from the movies resulting from these experiments enable quantification, through image analysis, of the antimicrobial penetration time, the size and rate of permeabilization of subpopulations exhibiting distinct susceptibilities, and the rate of biomass removal during exposure of bacterial biofilms to antimicrobial agents.
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Betty did you try downloading it then opening it? It's a .pdf so you should be able to zoom it as big as you need.
James
Posts: 872 | From New York City | Registered: Jun 2008
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Pinelady
Frequent Contributor (5K+ posts)
Member # 18524
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I think after reading this describing multipal
organisms and reading the research of Dr. Mary Enig
PhD who describes the effects on coconut oil on
virus' I am not sure we should not all be doing
some coconut. Thanks for the article.
-------------------- Suspected Lyme 07 Test neg One band migrating in IgG region unable to identify.Igenex Jan.09IFA titer 1:40 IND IgM neg pos 31 +++ 34 IND 39 IND 41 IND 83-93 + DX:Neuroborreliosis Posts: 5850 | From Kentucky | Registered: Dec 2008
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