Browsing by Author "Rupp, Cory J."

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Biofilm material properties as related to shear-induced deformation and detachment phenomena
(2002-12) Stoodley, Paul; Cargo, R.; Rupp, Cory J.; Wilson, Suzanne; Klapper, Isaac
Biofilms of various Pseudomonas aeruginosa strains were grown in glass flow cells under laminar and turbulent flows. By relating the physical deformation of biofilms to variations in fluid shear, we found that the biofilms were viscoelastic fluids which behaved like elastic solids over periods of a few seconds but like linear viscous fluids over longer times. These data can be explained using concepts of associated polymeric systems, suggesting that the extracellular polymeric slime matrix determines the cohesive strength. Biofilms grown under high shear tended to form filamentous streamers while those grown under low shear formed an isotropic pattern of mound-shaped microcolonies. In some cases, sustained creep and necking in response to elevated shear resulted in a time-dependent fracture failure of the "tail" of the streamer from the attached upstream "head." In addition to structural differences, our data suggest that biofilms grown under higher shear were more strongly attached and were cohesively stronger than those grown under lower shears.
Commonality of elastic relaxation times in biofilms
(2004-08) Shaw, T.; Winston, Matthew T.; Rupp, Cory J.; Klapper, Isaac; Stoodley, Paul
Biofilms, sticky conglomerations of microorganisms and extracellular polymers, are among the Earth's most common life forms. One component for their survival is an ability to withstand external mechanical stress. Measurements indicate that biofilm elastic relaxation times are approximately the same (about 18 min) over a wide sample of biofilms though other material properties vary significantly. A possible survival significance of this time scale is that it is the shortest period over which a biofilm can mount a phenotypic response to transient mechanical stress.
Detachment and other dynamic processes in bacterial biofilms
(2001) Stoodley, Paul; Wilson, Suzanne; Cargo, R.; Piscitteli, C.; Rupp, Cory J.
Rheology of biofilms
(2003) Winston, Matthew T.; Rupp, Cory J.; Vinogradov, A. M.; Towler, Brett William; Adams, Heather; Stoodley, Paul
The paper describes an experimental study concerning the mechanical properties of bacterial biofilms formed from the early dental plaque colonizer Streptoccocus mutans and pond water biofilms. Experiments reported in this paper demonstrate that both types of biofilms exhibit mechanical behavior similar to that of rheological fluids. The time-dependent properties of both biofilms have been modeled using the principles of viscoelasticity theory. The Burger model has been found to accurately represent the response of both biofilms for the duration of the experiments. On this basis, the creep compliances of both biofilms have been characterized, and the respective relaxation functions have been determined analytically.
Rheology of biofilms formed from the dental plaque pathogen Streptococcus mutans
(2004-01) Vinogradov, A. M.; Winston, Matthew T.; Rupp, Cory J.; Stoodley, Paul
Here we describe an experimental study of the mechanical properties of bacterial biofilms formed from the early dental plaque colonizer Streptococcus mutans. The S. mutans biofilms demonstrated the behavior of rheological fluids, with properties similar to those of organic polymers and other biological fluids. The time-dependent response of the biofilms was modeled on the basis of principles of viscoelasticity theory. The static and dynamic responses were defined in terms of the creep compliance, storage and loss moduli, and viscosity. The creep compliance and stress relaxation functions of S. mutans biofilms were characterized using the Burger model. Implications for developing more effective mechanical removal strategies of dental plaque biofilms are discussed.
Viscoelastic fluid description of bacterial biofilm material properties
(2002-09) Klapper, Isaac; Rupp, Cory J.; Cargo, R.; Purevdorj, B.; Stoodley, Paul
A mathematical model describing the constitutive properties of biofilms is required for predicting biofilm deformation, failure and detachment in response to mechanical forces. Laboratory observations indicate that biofilms are viscoelastic materials. Likewise, current knowledge of biofilm internal structure suggests modeling biofilms as associated polymer viscoelastic systems. Supporting experimental results and a system of viscoelastic fluid equations with a linear Jeffreys viscoelastic stress-strain law are presented here. This system of equations is based on elements of associated polymer physics and is also consistent with presented and previous experimental results. A number of predictions can be made. One particularly interesting result is the prediction of an elastic relaxation time on the order of a few minutes: biofilm disturbances on shorter time scales produce an elastic response, biofilm disturbances on longer time scales result in viscous flow, i.e., non-reversible biofilm deformation. Although not previously recognized, evidence of this phenomenon is in fact present in recent experimental results.
Viscoelastic properties of a mixed culture biofilm from rheometer creep analysis
(2003-10) Towler, Brett William; Rupp, Cory J.; Cunningham, Alfred B.; Stoodley, Paul
The mechanical properties of mixed culture biofilms were determined by creep analysis using an AR1000 rotating disk rheometer. The biofilms were grown directly on the rheometer disks which were rotated in a chemostat for 12 d. The resulting biofilms were heterogeneous and ranged from 35 microns to 50 microns in thickness. The creep curves were all viscoelastic in nature. The close agreement between stress and strain ratio of a sample tested at 0.1 and 0.5 Pa suggested that the biofilms were tested in the linear viscoelastic range and supported the use of linear viscoelastic theory in the development of a constitutive law. The experimental data was fit to a 4-element Burger spring and dashpot model. The shear modulus (G) ranged from 0.2 to 24 Pa and the viscous coefficient (eta) from 10 to 3000 Pa. These values were in the same range as those previously estimated from fluid shear deformation of biofilms in flow cells. A viscoelastic biofilm model will help to predict shear related biofilm phenomena such as elevated pressure drop, detachment, and the flow of biofilms over solid surfaces.
Viscoelasticity of Staphylococcus aureus biofilms in response to fluid shear allows resistance to detachment and facilitates rolling migration
(2005-04) Rupp, Cory J.; Fux, C. A.; Stoodley, Paul
Staphylococcus aureus is a leading cause of catheter-related bloodstream infections and endocarditis. Both involve (i) biofilm formation, (ii) exposure to fluid shear, and (iii) high rates of dissemination. We found that viscoelasticity allowed S. aureus biofilms to resist detachment due to increased fluid shear by deformation, while remaining attached to a surface. Further, we report that S. aureus microcolonies moved downstream by rolling along the lumen walls of a glass flow cell, driven by the flow of the overlying fluid. The rolling appeared to be controlled by viscoelastic tethers. This tethered rolling may be important for the surface colonization of medical devices by nonmotile bacteria.