biofilm 131111
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Biofilm Formation
Biofilm Concept
A biofilm is a structured community of bacterial cells enclosed in a self-produced extracellularpolymeric matrix (EPS) and adherent to inert or living surfaces (Costerton, 1999). However,eukaryotes are also known to reside inside biofilms: Candida albicans, a common oral and
genital pathogen, is a diploid fungus. Protozoans also commonly found inside stream biofilms1.
Biofilms are generally resistant
to antibiotics, disinfectants and cleaning fluids2.
Biofilms are considered the predominant state in which microbes are found in their natural
environment.
There are beneficial biofilms like Pseudomonas fluorescens biofilms that grow on the surface of
plant roots prevent the growth of fungal pathogens. Biofilms that grow on ingested plant materialwithin the rumen aid efficient breakdown of the plant which in turn provides the ruminant with
energy which is converted to meat and milk.
Cells within a biofilm are commonly phenotypically and genotypically distinct to their
planktonic counterparts e.g. E.coli do not possess fimbriae within biofilms but do when in the
planktonic phase. Indeed there are many genes which are expressed differently within thebiofilm and planktonic modes of growth.
Biofilm Distribution
Biofilms are dominant communitiesmore than half of Earths biomass is biofilm
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. Biofilmcommunities are ubiquitous.
Biofilm Development
Biofilms develop in five stages:
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1. Initial (reversible) attachment of cells to the surface by adhesins, receptors and non-specific mechanisms that rely on physical-chemical forces such as van-der Waals forces.
2. Irreversible attachment by production of EPS resulting in more firmly adhered.3. Maturation I. Early development of biofilm architecture.4. Maturation II. Maturation of biofilm architecture, attachment of other organisms
competition, organization to create pores, channels.
5. Dispersion of single cells from the biofilm.Fist, cells attach to the substrate surface (human tissue, glass, rocks, etc.). During this initial
step bacteria are often seen spinning, vibrating or even moving across the substrate surface.Spinning occurs when the body of bacteria is attached to by flagella, as these extensions are still
rotating. Vibration is seen when the water molecules are striking the loosely attached cells
(Brownian motion). As the number of cells increases, they move toward one another and form
aggregations. This allows for testing the micro-environment they are going to colonise before
irreversibly attaching.
Secondary colonizers co-adhere with organisms that first attached to the surface which results in
multi-species biofilm. Recruitment may be random or specific. Water is progressively removed
from the spaces in-between cells. Attachment causes the quorum sensing induction of genes
responsible for the production of compounds found in the matrix of developing biofilms. and thecells enclose themselves in a polymeric matrix that they produce. This stage is irreversible.
Mature biofilms are a complex uneven structure of dormant and actively growing bacteriacolonies of different species. The overall structure is formed along with further enzymes,
excretory products and small channels, as well as accumulated non-living material.
Planktonic cell will leave the biofilm and colonise a different surface. Biofilm extracellular
matrix degrading enzymes, such as dispersin B and deoxyribonuclease, may play a role in
biofilm dispersal. Dispersal may be achieved by means of abrasion and sloughing off.
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Quorum Sensing
Bacteria use quorum sensing to coordinate certain behaviours based on the local density of the
bacterial population. Different species use different molecules for communication; some sense
only their own molecules, others sense their own and other species molecules:
Autoinducer-2 (Al-2) in both Gram-positive and Gram-negative bacteria, N-acyl Homoserine lactones (AHL) in Gram-negative bacteria, and oligopeptides in Gram-positive bacteria
Revision
A biofilm is a complex aggregation of microorganisms found inside, or associated with, apolymeric matrix. Or simply, communities of microorganisms attached to a surface.
Organisms undergo major changes during the transition from planktonic (free-swimming)organisms to biofilm cells.
Biofilms are everywhere. Most microorganisms live in biofilms.
Five stages of biofilm development: 1. Initial reversible attachment; 2. Irreversibleattachment; 3. Early development of biofilm architecture; 4. Maturation of biofilm
architecture; 5. Dispersion.
Quorum sensing is a density-dependent mechanism allowing bacteria to co-ordinate theirgene expression.