Browsing by Author "Lappin-Scott, H. M."

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Assessment of a chemostat-coupled modified robbins device to study biofilms
(1995-10) Jass, J.; Costerton, J. William; Lappin-Scott, H. M.
The combination of a modified Robbins device (MRD) attached to the effluent line of a continuous cultivation vessel was assessed by the adhesion of planktonic bacteria maintained at a controlled growth rate. This combination of a chemostat and an MRD provides a large number of sample surfaces for monitoring both the formation and control of biofilms over extended periods of time. This apparatus was used to monitor the colonization of two soil isolates,Pseudomonas fluorescens (EX101) andPseudomonas putida (EX102) onto silastic rubber surfaces. At a similar μrel, both bacteria attached to the silastic, howeverP. fluorescens formed confluent, dense biofilms in less than 24 h, whereasP. putida adhered as single cells or microcolonies after the same period. The metabolic activity, measured by INT-formazan formation, was similar for both organisms with a peak at 6 h of colonization and a subsequent decrease after 24 h. Long term colonization studies ofP. fluorescens produced a population of greater than 9.5 log cfu cm−2 at 28 days demonstrating the advantages of the chemostat-MRD association. This technique proved to be successful for studying bacterial adhesion and biofilm formation in tubular devices by bacterial populations at controlled and low growth rates.
Biofilm formation by the rapidly growing mycobacterial species mycobacterium fortuitum
(1998-11) Hall-Stoodley, Luanne; Lappin-Scott, H. M.
Rapidly growing mycobacteria (RGM) are found in soil and diverse aquatic environments. Two species, Mycobacterium fortuitum and Mycobacterium chelonae, are associated with disease and are difficult to eradicate. Biofilm formation may be a contributing factor to their mode of transmission and their resistance to antimicrobial agents. We investigated the ability of the RGM species M. fortuitum to colonise surfaces using a modified Robbins device. M. fortuitum formed dense biofilms within 48 h. The high numbers of sessile organisms recovered and the swiftness of colonisation suggest that M. fortuitum readily forms biofilms. These results suggest a novel mechanism for mycobacteria in evading antimicrobial treatment and also indicate that biofilms should be considered possible sites for mycobacterial contamination.
Biofilm structure and influence on biofouling under laminar and turbulent flows
(1999) Stoodley, Paul; Boyle, John D.; Cunningham, Alfred B.; Dodds, I.; Lappin-Scott, H. M.; Lewandowski, Zbigniew
Community structure and co-operation in biofilms
(2000) Stoodley, Paul; Hall-Stoodley, Luanne; Boyle, John D.; Jørgensen, Frieda; Lappin-Scott, H. M.
Consensus model of biofilm structure
(1997) Stoodley, Paul; Boyle, John D.; Dodds, I.; Lappin-Scott, H. M.
Detachment, surface migration, and other dynamic behavior in bacterial biofilms revealed by digital time-lapse imaging
(2001) Stoodley, Paul; Hall-Stoodley, Luanne; Lappin-Scott, H. M.
The effect of electrical currents and tobramycin on pseudomonas aeruginosa biofilms
(1995-09) Jass, J.; Costerton, J. William; Lappin-Scott, H. M.
The combined use of antibiotics with low levels of electrical current has been reported to be more effective in controlling biofilms (the bioelectric effect) than antibiotics alone. An electrical colonisation cell was designed to study the effect of antibiotics on biofilms formed on a dialysis membrane away from the electrode surface. To avoid the electrochemical generation of toxic products,Pseudomonas aeruginosa biofilms were formed in minimal salts medium that excluded chloride-containing compounds. Under these conditions, electrical currents of up to 20 mA cm−2 did not prevent biofilm formation or have any detrimental effect on an established biofilm. Tobramycin alone at concentrations of 10 μg ml−1 did not affect the biofilm, but were significantly enhanced by 9 mA cm−2. The effect of tobramycin concentrations of 25 μg ml−1 were enhanced by a 15 mA cm−2 electrical current. In both cases higher levels of electrical current, up to 20 mA cm−2, did not further enhance the effect of the antibiotic. The possible mechanisms of action of the bioelectric effect have been reported to involve electrophoresis, iontophoresis and electroporesis, thus overcoming the biofilm biomass and cell wall barriers. Our results suggest that other factors may also be important, such as the metabolic activity and growth rate of the bacteria. Such factors may be critical in maximising antibiotic efficacy.
Establishment of experimental biofilms using the modified robbins device and flow cells
(1999) Hall-Stoodley, Luanne; Rayner, Joanna; Stoodley, Paul; Lappin-Scott, H. M.
Recent studies have shown that biofilms (a complex organization of bacterial cells present at a surface or interface, which produces a slime-like matrix) represent the principal form of bacterial growth in all environments studied to date (1). There are numerous advantages to bacteria growing in biofilms. These include extended protection against environmental changes, antimicrobial agents such as chemical disinfectants and antibiotics (2) and grazing predators such as amebae (3), as well as providing increased access to limited nutrients (4). Biofilms are of interest in medical, industrial, and natural environments for several reasons. For example, they can act as reservoirs from which the dissemination of pathogens may occur. Legionella pneumophila has been shown to be harbored within biofilms formed within drinking water pipelines (5). Similarly, it is well established that biofilms can colonize numerous types of medical implants (6). In industrial systems, detrimental effects may occur following biofilm growth such as reductions in heat-transfer efficiency and flow capacity. Biofouling may also markedly increase corrosion (7). Finally, biofilms represent a bacterial architecture that may support genetic transfer, nutrient utilization, and biodegradation (8).
Experimental biofilms and their applications in the study of environmental processes
(1999) Rayner, Joanna; Lappin-Scott, H. M.
The Formation of Migratory Ripples in a Mixed Species Bacterial Biofilm Growing in Turbulent Flow
(1999-09) Stoodley, Paul; Lewandowski, Zbigniew; Boyle, John D.; Lappin-Scott, H. M.
Mixed-species biofilms, consisting of Klebsiella pneumoniae, Pseudomonas aeruginosa, Pseudomonas fluorescens and Stenotrophomonas maltophilia, were grown in glass flow cells under either laminar or turbulent flow. The biofilms grown in laminar flow consisted of roughly circular-shaped microcolonies separated by water channels. In contrast, biofilm microcolonies grown in turbulent flow were elongated in the downstream direction, forming filamentous ‘streamers’. Moreover, biofilms growing in turbulent flow developed extensive patches of ripple-like structures between 9 and 13 days of growth. Using time-lapse microscopic imaging, we discovered that the biofilm ripples migrated downstream. The morphology and the migration velocity of the ripples varied with short-term changes in the bulk liquid flow velocity. The ripples had a maximum migration velocity of 800 μm h−1 (2.2 × 10−7 m s−1) when the liquid flow velocity was 0.5 m s−1(Reynolds number = 1800). This work challenges the commonly held assumption that biofilm structures remain at the same location on a surface until they eventually detach.
Growth and detachment of cell clusters from mature mixed species biofilms
(2001-12) Stoodley, Paul; Wilson, Suzanne; Hall-Stoodley, Luanne; Boyle, John D.; Lappin-Scott, H. M.; Costerton, J. William
Detachment from biofilms is an important consideration in the dissemination of infection and the contamination of industrial systems but is the least-studied biofilm process. By using digital time-lapse microscopy and biofilm flow cells, we visualized localized growth and detachment of discrete cell clusters in mature mixed-species biofilms growing under steady conditions in turbulent flow in situ. The detaching biomass ranged from single cells to an aggregate with a diameter of approximately 500 µm. Direct evidence of local cell cluster detachment from the biofilms was supported by microscopic examination of filtered effluent. Single cells and small clusters detached more frequently, but larger aggregates contained a disproportionately high fraction of total detached biomass. These results have significance in the establishment of an infectious dose and public health risk assessment.
Growth of microorganisms on surfaces
(1995) Korber, D. R.; Lawrence, J. R.; Lappin-Scott, H. M.; Costerton, J. William
Influence of electric fields and ph on biofilm structure as related to the bioelectric effect
(1997) Stoodley, Paul; Lappin-Scott, H. M.
The influence of fluid shear and AlCl3 on the material properties of Pseudomonas aeruginosa PAO1 and Desulfovibrio sp. EX265 biofilms
(2001) Stoodley, Paul; Jacobsen, A.; Dunsmore, B. C.; Purevdorj, B.; Wilson, Suzanne; Lappin-Scott, H. M.; Costerton, J. William
An understanding of the material properties of biofilms is important when describing how biofilms physically interact with their environment. In this study, aerobic biofilms of Pseudomonas aeruginosa PAO1 and anaerobic sulfate-reducing bacteria (SRB) biofilms of Desulfovibrio sp. EX265 were grown under different fluid shear stresses (tg) in a chemostat recycle loop. Individual biofilm microcolonies were deformed by varying the fluid wall shear stress (tw). The deformation was quantified in terms of strain (e), and the relative strength of the biofilms was assessed using an apparent elastic coefficient (Eapp) and residual strain (er) after three cycles of deformation. Aluminum chloride (AlCl3) was then added to both sets of biofilm and the tests repeated. Biofilms grown under higher shear were more rigid and had a greater yield shear stress than those grown under lower shear. The addition of AlCl3 resulted in a significant increase in Eapp and also increased the yield point. We conclude that the strength of the biofilm is in part dependent on the shear under which the biofilm was grown and that the material properties of the biofilm may be manipulated through cation cross-linking of the extracellular polysaccharide (EPS) slime matrix.
The influence of fluid shear on the structure and material properties of sulphate-reducing bacterial biofilms
(2002-12) Dunsmore, B. C.; Jacobsen, A.; Hall-Stoodley, Luanne; Bass, C. J.; Lappin-Scott, H. M.; Stoodley, Paul
Biofilms of sulphate-reducing Desulfovibrio sp. EX265 were grown in square section glass capillary flow cells under a range of fluid flow velocities from 0.01 to 0.4 m/s (wall shear stress, τw, from 0.027 to 1.0 N/m2). In situ image analysis and confocal scanning laser microscopy revealed biofilm characteristics similar to those reported for aerobic biofilms. Biofilms in both flow cells were patchy and consisted of cell clusters separated by voids. Length-to-width ratio measurements (lc:wc) of biofilm clusters demonstrated the formation of more “streamlined” biofilm clusters (lc:wc=3.03) at high-flow velocity (Reynolds number, Re, 1200), whereas at low-flow velocity (Re 120), the lc:wc of the clusters was approximately 1 (lc:wc of 1 indicates no elongation in the flow direction). Cell clusters grown under high flow were more rigid and had a higher yield point (the point at which the biofilm began to flow like a fluid) than those established at low flow and some biofilm cell aggregates were able to relocate within a cluster, by travelling in the direction of flow, before attaching more firmly downstream.
Influence of hydrodynamics and nutrients on biofilm structure
(1999-12) Stoodley, Paul; Dodds, I.; Boyle, John D.; Lappin-Scott, H. M.
Hydrodynamic conditions control two interlinked parameters; mass transfer and drag, and will, therefore, significantly influence many of the processes involved in biofilm development. The goal of this research was to determine the effect of flow velocity and nutrients on biofilm structure. Biofilms were grown in square glass capillary flow cells under laminar and turbulent flows. Biofilms were observed microscopically under flow conditions using image analysis. Mixed species bacterial biofilms were grown with glucose (40 mg/l) as the limiting nutrient. Biofilms grown under laminar conditions were patchy and consisted of roughly circular cell clusters separated by interstitial voids. Biofilms in the turbulent flow cell were also patchy but these biofilms consisted of patches of ripples and elongated ‘streamers' which oscillated in the flow. To assess the influence of changing nutrient conditions on biofilm structure the glucose concentration was increased from 40 to 400 mg/l on an established 21 day old biofilm growing in turbulent flow. The cell clusters grew rapidly and the thickness of the biofilm increased from 30 μ to 130 μ within 17 h. The ripples disappeared after 10 hours. After 5 d the glucose concentration was reduced back to 40 mg/l. There was a loss of biomass and patches of ripples were re-established within a further 2 d.
Introduction to microbial biofilms
(1995) Costerton, J. William; Lappin-Scott, H. M.
Microbial Biofilms
(1995) Costerton, J. William; Lewandowski, Zbigniew; Caldwell, D. E.; Korber, D. R.; Lappin-Scott, H. M.
Microbial detachment from biofilms
(2000) Moore, G. F.; Dunsmore, B. C.; Jones, S. M.; Smejkal, C. W.; Jass, J.; Stoodley, Paul; Lappin-Scott, H. M.
Oscillation characteristics of biofilm streamers in turbulent flowing water as related to drag and pressure drop
(1998-03) Stoodley, Paul; Lewandowski, Zbigniew; Boyle, John D.; Lappin-Scott, H. M.
Mixed population biofilms consisting of Pseudomonas aeruginosa, P. fluorescens, and Klebsiella pneumoniae were grown in a flow cell under turbulent conditions with a water flow velocity of 18 cm/s (Reynolds number, Re, =1192). After 7 days the biofilms were patchy and consisted of cell clusters and streamers (filamentous structures attached to the downstream edge of the clusters) separated by interstitial channels. The cell clusters ranged in size from 25 to 750 μm in diameter. The largest clusters were approximately 85 μm thick. The streamers, which were up to 3 mm long, oscillated laterally in the flow. The motion of the streamers was recorded at various flow velocities up to 50.5 cm/s (Re 3351) using confocal scanning laser microscopy. The resulting time traces were evaluated by image analysis and fast Fourier transform analysis (FFT). The amplitude of the motion increased with flow velocity in a sigmoidal shaped curve, reaching a plateau at an average fluid flow velocity of approximately 25 cm/s (Re 1656). The motion of the streamers was possibly limited by the flexibility of the biofilm material. FFT indicated that the frequency of oscillation was directly proportional to the average flow velocity (u(ave)) below 9.5 cm/s (Re 629). At u(ave) greater than 9.5 cm/s, oscillation frequencies were above our measurable frequency range (0.12–6.7 Hz). The oscillation frequency was related to the flow velocity by the Strouhal relationship, suggesting that the oscillations were possibly caused by vortex shedding from the upstream biofilm clusters. A loss coefficient (k) was used to assess the influence of biofilm accumulation on pressure drop. The k across the flow cell colonized with biofilm was 2.2 times greater than the k across a clean flow cell. ©1998 John Wiley & Sons, Inc. Biotechnol Bioeng 57: 536-544, 1998.