fundamentals and applications of biofilms biofilm...
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Fundamentals and Applications of BiofilmsBiofilm Control: Engineering and Microbiological ConsiderationChing-Tsan Huang (黃慶璨)Office: Agronomy Hall, Room 111Tel: (02) 33664454E-mail: [email protected]
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Why Biofilm Control?The phenomena
Increase transfer resistance of mass, heat and momentumDeteriorate materials biofilm attachedHealth risk
The consequencesEnergy lossesIncrease capital costUnscheduled turnaroundQuality control problemsSafety problems
http://www.zetacorp.com/biocorrosion.shtml
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Biofilm Control
Different considerationsEngineering considerationMicrobiological considerationMolecular level consideration
Type of biofilm controlPrevention Killing Removing
Biofilms: Formation Process
By P. DirckxSubstratum
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Common biofilm control strategy
From: Biofilmbook.hypertexbook.com
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Biofilm Control ApproachesMechanical cleaningOn-line: Backwash of condensers and heat
exchangers; Debris filers; Recirculating sponge balls.
Off-line: Passing air and water; Brushing; Scraping.
Advantages: better biofilm removal, no harm to environments.
Disadvantages: impractical to large scale, shut-down required.
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Antimicrobial treatmentAdvantages: Reduce time of shut-down, applicable to current systems, less cost
Disadvantages: less effective, environmental concern
New materials that prevent bacterial attachmentAdvantages: actually remove biofilms, no harm to environments.
Disadvantages: required further development.
Biofilm Control Approaches
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Biofilm Resistance
Teitzel, G. M. et al. 2003. Appl. Environ. Microbiol. 69(4):2313-2320
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Oxidizing BiocidesChlorine (Sodium hyperchlorite)
Cl2 + H2O HOCl + H+ + Cl-
Bromine (Sodium hyperbromite)Br- + HOCl HOBr + Cl-
Halogenated organic compoundBromochlorohydatoin
Amines: mono-, di-, trichloramineHOCl + NH3 NH2Cl + H2OHOCl + NH2Cl NHCl2 + H2OHOCl + NHCl2 NCl3 + H2O
Chlorine dioxide (oil field)Ozone (O3) Need a costly generatorHydrogen peroxide (nuclear power plant)
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Types of Antimicrobial Agents
Nonoxidizing biocidesGlutaldehydeFormaldehydeEGTA (calcium-specific chelant)
AntibioticsAmpicillinKanamycinTetracycline
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Biofilm Resistant Factor
DefinitionSurviving fraction: suspended vs biofilm culturesLog (Xo/X), Log (Bo/B)
Resistant factor = Log (Xo/X)
Log (Bo/B)
Oxidizing, Nonoxidizing biocides and antibiotics
Resistant factors vs biofilm density
&more
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From: Biofilmbook.hypertexbook.com
Diffusion Limitation within Biofilms
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Biofilm Resistance Mechanism
& others
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Mechanism of Biofilm Resistance
Antimicrobial depletionReactive antimicrobial agents (chlorine) react or neutralize with extracellular polymers.Antimicrobial agents (antibiotics) are adsorbed by EPS.Antimicrobial agents (antibiotics, H2O2) are inactivated by enzyme reactions.
Transport limitationMass transfer resistance increases with increasing biofilm thickness
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Biofilm Control Suggestion
When transport is limitingTreat the biofilm when it is thin
Decrease external mass transfer resistance to biocide delivery into the biofilm
Weigh both biocide power and reactivity when selecting a biocide
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Biofilm Control Approaches:Transport-based
Organohyperchlorite compounds.
Blind test of surfactants.
Ultrasonic enhancement.
Bioelectric treatment.
Enhancer
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Biofilm Control ResearchSolution-oriented approaches
Why are biofilms hard to kill?
How can we control biofilms better?
From fundamental research to
technology development.
From green to $.
Less energy, less materialsEnvironment friendly
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Transport limited
Physiologylimited
Biofilm resistanceTransport or physiology limited?
Srinivasan et al.(1995) Biotech. Bioeng. 46: 553-560.
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Biofilm Resistance Mechanism
& others
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Physiological limitationSuspended cultures: well mixed, cells swim freely, nutrients diffusion is not a problem.
Biofilm cultures: Nutrient gradients, physiological activity changed.
Starvation: induced synthesis of several enzymes. Example: phosphate starvation leads to the induction of alkaline phosphatase.
Mechanism of Biofilm Resistance
21Starvation on Antibiotic Susceptibility
rich, less
starvation, less
rich, more
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Adaptation When biofilms are exposed to antimicrobial treatment, biofilm cells will adjust their physiological activity in response to the foreign chemical challenges.
Mechanism of Biofilm Resistance
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Growth Rate on Antibiotic Susceptibility
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Growth Rate Dependent Killing
0.1 h-1
0.32 h-1
0.41 h-1
more
Duguid et al (1992) J. Antimicrob. Chemother. 30: 803-810.
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http://www.erc.montana.edu/MultiCellStrat/06-Meeting_Antimic-Challenge/SuscpHypotheses.htm
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Regrowth (recovery):A rapid resumption of biofilms after antimicrobial
treatment was terminated. The remaining biofilms contain enough viable organisms. The residual biofilm imparts an increased relative roughness to the surface and thus enhances transport and sorption of microbial cells and other compounds to the surface. Some oxidizing antimicrobial agents preferentially removes EPS and not biofilm cells. EPS is rapidly created by surviving organisms.
Regrowth after Antimicrobial Treatment
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Biofilm Control Suggestion
When physiology is limiting
Stimulate growth to place microorganisms in a more susceptible state
Screen for antimicrobial agents based on their efficacy against nongrowing bacteria
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P
Smart Biocide
BOMBBOMB
P