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  • biofilm  (8)
  • Wiley-Blackwell  (8)
  • American Meteorological Society (AMS)
  • American Physical Society
  • 1
    Electronic Resource
    Electronic Resource
    A review of experimental measurements of effective diffusive permeabilities and effective diffusion coefficients in biofilms (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 261-272 
    Details
    ISSN: 0006-3592
    Keywords: effective diffusive permeability ; diffusion coefficient ; biofilm ; cell density ; review ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental measurements of effective diffusive permeabilities and effective diffusion coefficients in biofilms are reviewed. Effective diffusive permeabilities, the parameter appropriate to the analysis of reaction-diffusion interactions, depend on solute type and biofilm density. Three categories of solute physical chemistry with distinct diffusive properties were distinguished by the present analysis. In order of descending mean relative effective diffusive permeability (De/Daq) these were inorganic anions or cations (0.56), nonpolar solutes with molecular weights of 44 or less (0.43), and organic solutes of molecular weight greater than 44 (0.29). Effective diffusive permeabilities decrease sharply with increasing biomass volume fraction suggesting a serial resistance model of diffusion in biofilms as proposed by Hinson and Kocher (1996). A conceptual model of biofilm structure is proposed in which each cell is surrounded by a restricted permeability envelope. Effective diffusion coefficients, which are appropriate to the analysis of transient penetration of nonreactive solutes, are generally similar to effective diffusive permeabilities in biofilms of similar composition. In three studies that examine diffusion of very large molecular weight solutes ( 〉 5000) in biofilms, the average ratio of the relative effective diffusion coefficient of the large solute to the relative effective diffusion coefficient of either sucrose or fluorescein was 0.64, 0.61, and 0.36. It is proposed that large solutes are effectively excluded from microbial cells, that small solutes partition into and diffuse within cells, and that ionic solutes are excluded from cells but exhibit increased diffusive permeability (but decreased effective diffusion coefficients) due to sorption to the biofilm matrix. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:261-272, 1998.
    Additional Material: 5 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative analysis of biofilm thickness variability (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 45 (1995), S. 503-510 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; thickness ; heterogeneity ; roughness ; microscopy ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The thickness variability of biofilms of Pseudomonas aeruginosa, Klebsiella pneumoniae, and the binary population combination of these two species was quantified. The experimental method involved cryoembedding biofilms with a commercial tissue embedding agent, sectioning, and applying image analysis to construct thickness profiles along linear transects (up to 1 cm in length) across the substratum. Biofilms embedded and sectioned by this method were locally as thin as a single cell attached to the surface (〈5 μm) and as thick as 1000 μm. Week-old biofilms of three different species compositions displayed distinct structural features as indicated by their mean thicknesses and by a roughness coefficient. Monopopulation biofilms of P. aeruginosa (29 μm mean thickness) or K. pneumoniae (100 μm mean thickness) were thinner than the binary population biofilm (400 μm mean thickness). A roughness coefficient developed in this investigation corroborated the qualitative visual characterization of P. aeruginosa biofilms as relatively uniformly thick (mean roughness coefficient 0.15), K. pneumoniae biofilms as patchy (mean roughness coefficient 1.14), and the binary population biofilm as intermediate (mean roughness coefficient 0.26). Whereas P. aeruginosa and binary population biofilms covered the substratum completely, significant areas of essentially bare substratum were apparent in K. pneumoniae biofilms. The patchiness of K. pneumoniae biofilms may be due to the fact that this organism is nonmotile. A spatial correlation analysis of the thickness data indicated that thickness measurements were still correlated even when separated by distances that exceeded the mean biofilm thickness. Cell aggregates, some of them hundreds of microns in size, were observed in the effluent of K. pneumoniae and binary population biofilm reactors. Measurements of thickness variability and other observations reported in this article provide a quantitative basis for analysis of microscale structural heterogeneity of biofilms. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260450607
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  • 3
    Electronic Resource
    Electronic Resource
    A model of biofilm detachment (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 41 (1993), S. 111-117 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; detachment ; model ; physiology ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A general mathematical framework for modeling biofilm detachment is presented. The approach is founded on a material balance on biomass that equates the detachment rate to the product of a detachment frequency and a detaching particle mass. The model provides a theoretical basis for deriving many of the empirical detachment rate expressions in common use and can thus lend some insight into their physical and biological significance. By allowing for variation in the detachment frequency with depth in the biofilm, the model permits derivation of detachment expressions that reflect a dependence on chemical or physiological gradients in the biofilm. Analysis of literature data sets from two different biofilm systems suggests, in both cases, that detachment is a growth-associated phenomenon. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260410115
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  • 4
    Electronic Resource
    Electronic Resource
    Transport of 1-μm latex particles in pseudomonas aeruginosa biofilms (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 42 (1993), S. 111-117 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; particle ; Pseudomonas aeruginosa ; transport ; roughness ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Fluorescent latex microbeads added to a Pseudomonas aeruginosa biofilm as tracers of particle movement penetrated the biofilm and remained in it much longer than predicted by a model of advective displacement due to cell growth. Beads with a nominal diameter of 1 μm that were added in the bulk fluid became distributed throughout the biofilm depth. Some microbeads penetrated to the substratum within the 24-h bead addition period. The biofilms had a mean thickness of approximately 34 μm but have been previously shown to be quite rough. Measured rates of bead release from the biofilm corresponded to first order time coefficients of 0.01-0.03 h-1. These bead release rates were approximately an order of magnitude less than the predicted time scale of advective transport, which is just the experimentally measured specific cellular growth rate of 0.15 h-1. Computer simulations of bead transport using the biofilm model BIOSIM were compared with bead release rate data and with bead position distributions within the biofilm as determined by microscopic examination of thin cross sections of embedded biofilm. The model predicted much faster release of beads from the biofilm than actually occurred. It is hypothesized that both the ability of beads to penetrate the biofilm and the unexpectedly low advective displacement velocity of particles in the biofilm were due to the rough nature of the biofilm. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260420115
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling biocide action against biofilms (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 445-455 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; biocide ; disinfection ; reaction-diffusion ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A phenomenological model of biocide action against microbial biofilms was derived. Processes incorporated in the model include bulk flow in and out of a well-mixed reactor, transport of dissolved species into the biofilm, substrate consumption by bacterial metabolism, bacterial growth, advection of cell mass within the biofilm, cell detachment from the biofilm, cell death, and biocide concentration-dependent disinfection. Simulations were performed to analyze the general behavior of the model and to perform preliminary sensitivity analysis to identify key input parameters. The model captured several general features of antimicrobial agent action against biofilms that have been observed widely by experimenters and practitioners. These included (1) rapid disinfection followed by biofilm regrowth, (2) slower detachment than disinfection, and (3) reduced susceptibility of microorganisms in biofilms. The results support the plausibility of a mechanism of biofilm resistance in which the biocide is neutralized by reaction with biofilm constituents, leading to a reduction in the bulk biocide concentration and, more significantly, biocide concentration gradients within the biofilm. Sensitivity experiments and analyses identified which input parameters influence key response variables. Each of three response variables was sensitive to each of the five input parameters, but they were most sensitive to the initial biofilm thickness and next most sensitive to the biocide disinfection rate coefficient. Statistical regression modeling produced simple equations for approximating the response variables for situations within the range of conditions covered by the sensitivity experiment. The model should be useful as a tool for studying alternative biocide control strategies. For example, the simulations suggested that a good interval between pulses of biocide is the time to minimum thickness. © 1996 John Wiley & Sons, Inc.
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  • 6
    Electronic Resource
    Electronic Resource
    Biofilm parameters influencing biocide efficacy (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 46 (1995), S. 553-560 
    Details
    ISSN: 0006-3592
    Keywords: biofilm ; disinfection ; detachment ; biofouling ; ecology ; biocide ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The influence of biofilm areal cell density, species composition, and the presence of abiotic particles on the disinfection and removal of bacterial biofilms by monochloramine was investigated. Mono- and binary population biofilms of Pseudomonas aeruginosa and Klebsiella pneumoniae were grown on stainless-steel slides in a continuous flow annular reactor. Biofilms were treated in the reactor with a pulse/step dose of 4 mg/L monochloramine for 2 h. Biofilm samples were disaggregated and assayed for colony formation on R2A agar and for total cell numbers by acridine orange direct counts. These data were used to determine apparent first order rate coefficients for the processes of disinfection and detachment. Disinfection rate coefficients exceeded detachment rate coefficients by as much as an order of magnitude and the two coefficients were poorly correlated (r = 0.272). The overall decay rate coefficient (disinfection plus detachment) depended strongly on the initial biofilm areal cell density. It displayed a parabolic dependence on cell density with a maximum near 108 cfu/cm2. This result points to multiple factors influencing biofilm susceptibility to antimicrobial challenge. Decay rates of K. pneumoniae measured in binary population biofilms were comparable with those measured in monopopulation biofilms (p = 0.61). P. aeruginosa decayed more slowly in biofilsm dominated by K. pneumoniae (p = 0.028), indicating some interaction between species. The presence of kaolin and calcium carbonate particles in the biofilm reduced disinfection efficacy. © 1995 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260460608
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  • 7
    Electronic Resource
    Electronic Resource
    Transport limitation of chlorine disinfection of Pseudomonas aeruginosa entrapped in alginate beads (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 93-100 
    Details
    ISSN: 0006-3592
    Keywords: disinfection ; chlorine ; transport ; gel bead ; biofilm ; reaction-diffusion ; Pseudomonas aeruginosa ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An artificial biofilm system consisting of Pseudomonas aeruginosa entrapped in alginate and agarose beads was used to demonstrate transport limitation of the rate of disinfection of entrapped bacteria by chlorine. Alginate gel beads with or without entrapped bacteria consumed chlorine. The specific rate of chlorine consumption increased with increasing cell loading in the gel beads and decreased with increasing bead radius. The value of an observable modulus comparing the rates of reaction and diffusion ranged from less than 0.1 to 8 depending on the bead radius and cell density. The observable modulus was largest for large (3-mm-diameter) beads with high cell loading (1.8 × 109 cfu/cm3) and smallest for small beads (0.5 mm diameter) with no cells added. A chlorine microelectrode was used to measure chlorine concentration profiles in agarose beads (3.0 mm diameter). Chlorine fully penetrated cell-free agarose beads rapidly; the concentration of chlorine at the bead center reached 50% of the bulk concentration within approximately 10 min after immersion in chlorine solution. When alginate and bacteria were incorporated into an agarose bead, pronounced chlorine concentration gradients persisted within the gel bead. Chlorine did gradually penetrate the bead, but at a greatly retarded rate; the time to reach 50% of the bulk concentration at the bead center was approximately 46 h. The overall rate of disinfection of entrapped bacteria was strongly dependent on cell density and bead radius. Small beads with low initial cell loading (0.5 mm diameter, 1.1 × 107 cfu/cm3) experienced rapid killing; viable cells could not be detected (〈1.6 × 105 cfu/cm3) after 15 min of treatment in 2.5 mg/L chlorine. In contrast, the number of viable cells in larger beads with a higher initial cell density (3.0 mm diameter, 2.2 × 109 cfu/cm3) decreased only about 20% after 6 h of treatment in the same solution. Spatially nonuniform killing of bacteria within the beads was demonstrated by measuring the transient release of viable cells during dissolution of the beads. Bacteria were killed preferentially near the bead surface. Experimental results were consistent with transport limitation of the penetration of chlorine into the artificial biofilm arising from a reaction-diffusion interaction. The methods reported here provide tools for diagnosing the mechanism of biofilm resistance to reactive antimicrobial agents in such applications as the treatment of drinking and cooling waters. © 1996 John Wiley & Sons, Inc.
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  • 8
    Electronic Resource
    Electronic Resource
    Evidence of bacterial adaptation to monochloramine in Pseudomonas aeruginosa biofilms and evaluation of biocide action model (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 201-209 
    Details
    ISSN: 0006-3592
    Keywords: adaptation ; biofilm ; biocide ; disinfection ; model ; monochloramine ; Pseudomonas ; stress response ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A mathematical model of biocide action against microbial biofilm was tested experimentally by measuring the response of Pseudomonas aeruginosa biofilm to various doses of monochloramine. Pure culture biofilm was developed in continuous flow annular reactors for 7 days, then treated with a 2-, 4-, or 8-h dose of 2 or 4 mg L-1 monochloramine. Some experiments investigated repeated treatment. Disinfection and regrowth of the biofilm were observed by sampling the biofilm for viable and total cell areal densities for up to 100 h following the biocide treatment. A phenomenological mathematical model was fitted to experimental data sets and captured overall trends, but it could not simulate certain experimentally observed features. The model did simulate rapid disinfection followed by steady regrowth. It correctly predicted a much greater decrease in viable than in total cell densities and also correctly captured the shapes of these trajectories. Discrepancies between the model and data included the following: the model predicted faster regrowth than was experimentally observed, the model predicted that a second dose would be more effective than the first dose but the opposite was observed in the experiments, and parameters estimated by fitting one dose concentration could not be used to predict the results of a different dose concentration or a second dose. Discrepancies between model and the experiment were hypothesized to be due to an adaptive stress response by the bacteria, a process not included in the model. A practical implication of this work is that it is more effective to deliver monochloramine in a short concentrated dose as opposed to a longer dose of lower concentration. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 201-209, 1997.
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