Biomedical subjects

J D Boyle

Publications and source records attributed to J D Boyle.

At least 19 recordsLinked to original sources

PubMed2006

Quantification of the effect of flowrate on the rates of arrival and attachment to glass of Pseudomonas aeruginosa.

Sets of time lapse sequences (movies) of pseudomonad cells attaching in each of six flowcells operated at Reynolds numbers from 96-2220 were obtained over a 3-d period. The interval between images varied between 1 s and 24 min, which allowed a range of different cell behaviours to be observed. The rate of accumulation of the cells on the surface was determined for each flowrate. Analysis of the images showed that the residence time distributions of the attaching cells were of the same form as those recorded previously in the literature. This showed that up to 50% of the cells that arrived sufficiently close to the surface to be considered temporarily attached, left the surface within 1 s of arrival. Use of an analytically derived algorithm allowed the rate of arrival of the cells to be estimated. Data showed that for every cell attaching on a relatively permanent basis, between 20 and 35 cells arrived at the surface.

Bacterial Adhesion↗

PubMed2005

Flowing biofilms as a transport mechanism for biomass through porous media under laminar and turbulent conditions in a laboratory reactor system.

Fluid flow has been shown to be important in influencing biofilm morphology and causing biofilms to flow over surfaces in flow cell experiments. However, it is not known whether similar effects may occur in porous media. Generally, it is assumed that the primary transport mechanism for biomass in porous media is through convection, as suspended particulates (cells and flocs) carried by fluid flowing through the interstices. However, the flow of biofilms over the surfaces of soils and sediment particles, may represent an important flux of biomass, and subsequently affect both biological activity and permeability. Mixed species bacterial biofilms were grown in glass flow cells packed with 1 mm diameter glass beads, under laminar or turbulent flow (porous media Reynolds number = 20 and 200 respectively). The morphology and dynamic behavior reflected those of biofilms grown in the open flow cells. The laminar biofilm was relatively uniform and after 23 d had inundated the majority of the pore spaces. Under turbulent flow the biofilm accumulated primarily in protected regions at contact points between the beads and formed streamers that trailed from the leeward face. Both biofilms caused a 2 to 3-fold increase in friction factor and in both cases there were sudden reductions in friction factor followed by rapid recovery, suggesting periodic sloughing and regrowth events. Time-lapse microscopy revealed that under both laminar and turbulent conditions biofilms flowed over the surface of the porous media. In some instances ripple structures formed. The velocity of biofilm flow was on the order of 10 mum h(-1) in the turbulent flow cell and 1.0 mum h(-1) in the laminar flow cell.

Biofilms↗

PubMed2001

Growth and detachment of cell clusters from mature mixed-species biofilms.

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 microm. 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.

Biofilms↗

PubMed1999

Structural deformation of bacterial biofilms caused by short-term fluctuations in fluid shear: an in situ investigation of biofilm rheology.

The physical properties (rheology) of biofilms will determine the shape and mechanical stability of the biofilm structure and consequently affect both mass transfer and detachment processes. Biofilm viscoelasticity is also thought to increase fluid energy losses in pipelines. Yet there is very little information on the rheology of intact biofilms. This is due in part to the difficulty in using conventional testing techniques. The size and nature of biofilms makes them difficult to handle, while removal from a surface destroys the integrity of the sample. We have developed a method which allowed us to conduct simple stress-strain and creep experiments on mixed and pure culture biofilms in situ by observing the structural deformations caused by changes in hydrodynamic shear stress (tau(w)). The biofilms were grown under turbulent pipe flow (flow velocity (u) = 1 m/s, Reynolds number (Re) = 3600, tau(w) = 5. 09 N/m(2)) for between 12 and 23 days. The resulting biofilms were heterogeneous and consisted of filamentous streamers that were readily deformed by changes in tau(w). At tau(w) of 10.11 N/m(2) the streamers were flattened so that the thickness was reduced by 25%. We estimated that the shear modulus (G) of the mixed culture biofilm was 27 N/m(2) and the apparent elastic modulus (E(app)) of both biofilms was in the range of 17 to 40 N/m(2). The biofilms behaved like elastic and viscoelastic solids below the tau(w) at which they were grown but behaved like viscoelastic fluids at elevated tau(w). The implications of these results for fluid energy losses and the processes of mass transfer and detachment are discussed.

Bacteria↗

PubMed1999

The formation of migratory ripples in a mixed species bacterial biofilm growing in turbulent flow.

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 micromh(-1) (2.2 x 10(-7) m s(-1)) when the liquid flow velocity was 0.5 ms(-1) (Reynolds number=1,800). This work challenges the commonly held assumption that biofilm structures remain at the same location on a surface until they eventually detach.

Biofilms↗

PubMed1998

Oscillation characteristics of biofilm streamers in turbulent flowing water as related to drag and pressure drop.

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 microm in diameter. The largest clusters were approximately 85 microm 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.

Biofilms↗

PubMed1988

The life and death of Ismar Boas.

Dr. Ismar Boas (1858-1938) was the founder of the medical subspecialty of gastroenterology. In 1886, he opened in Berlin the first specialty clinic for the study of digestive diseases. In 1895, he founded the first journal devoted to gastroenterology. During his long and productive career, Boas was a pioneer in nearly all areas of his field. His most lasting scientific accomplishment is his work on occult bleeding, which first introduced the clinical importance of this abnormal finding for the early diagnosis of gastric carcinoma. Fifty years ago, in 1938, Ismar Boas killed himself as the Nazis occupied Vienna. In this article, we honor the memory of a great physician and retrace the circumstances of his death.

Gastroenterology↗

PubMed1982