Escherichia coli O157:H7 Requires Colonizing Partner to Adhere and Persist in a Capillary Flow Cell

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.