Browsing by Author "Klayman, Benjamin J."

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Escherichia coli O157:H7 Requires Colonizing Partner to Adhere and Persist in a Capillary Flow Cell
(2009-03) Klayman, Benjamin J.; Volden, Paul A.; Stewart, Philip S.; Camper, Anne K.
The ability of a strain of waterborne Escherichia coli O157:H7 to colonize a glass flow cell and develop microcolonies when grown alone and with Pseudomonas aeruginosa PAO1 was examined. When introduced alone, planktonic E. coli were unable to attach to the glass surface. When introduced simultaneously with P. aeruginosa (co-inoculation), the two species coadhered to the surface. When E. coli were introduced into a flow cell precolonized with a P. aeruginosa biofilm (precolonized), 10-fold more cells were retained than in the co-inoculated case. Both species were monitored nondestructively by time-lapse confocal microscopy, direct microscopy of the filtered effluent, and effluent plate counts. While more E. coli initially adhered in the precolonized system, E. coli microcolony formation occurred only in the co-inoculated system, where E. coli comprised 1% of the total surface-associated biovolume but greater than 50% of the biovolume near the edges of the flow cell. The hydrodynamics in the flow cell were evaluated using the finite volume analysis program CFX, revealing that shear stress was likely important in both initial attachment and steady-state colonization patterns. This research elucidates key factors which promote retention and subsequent biofilm development of E. coli O157:H7.
Measurements of accumulation and displacement at the single cell cluster level in Pseudomonas aeruginosa biofilms
(2008-09) Klayman, Benjamin J.; Klapper, Isaac; Stewart, Philip S.; Camper, Anne K.
Quantitative descriptions of biofilm growth and dynamics at the individual cell level are largely missing from the literature. To fill this gap, research was done to describe growth, accumulation and displacement patterns in developing Pseudomonas aeruginosa biofilms. A parent strain of PAO1 was labelled with either a cyan or yellow fluorescent protein. These were then grown in a flow cell biofilm together so that pockets of dividing cells could be identified and their accumulation and displacement tracked. This analysis revealed a pattern of exponential accumulation for all clusters followed by a stationary accumulation phase. A background ‘carpet’ layer of cells uniformly colonizing the surface exhibited zero net accumulation of bio-volume. The individual clusters were found to have a mean accumulation rate of 0.34 h-1 with a range of 0.28–0.41 h-1. Cluster accumulation rates were negatively correlated with cluster size; larger clusters accumulated volume at a slower rate (P < 0.001). Pockets of cells on the inside of clusters initially accumulated at a comparable rate to the cluster within which they resided, but later invariably exhibited zero to slightly negative accumulation despite continued exponential (positive) accumulation of the cluster. Expanding clusters were able to displace neighbouring cells from the surface, and larger clusters displaced smaller clusters. This work provides a more detailed quantitative experimental observation of biofilm behaviour than has been described previously.