Title

The effect of environmental stress on cell surface properties and their relation to microbial adhesion in feedlot Escherichia coli isolates

Date of Completion

January 2005

Keywords

Biology, Microbiology

Degree

Ph.D.

Abstract

We built an exhaustive inventory of extant Escherichia coli population from a bovine feedlot at the University of Connecticut. Approximately 280 E. coli isolates were isolated, and a total of 89 distinct operational taxonomic units (OTUs) were identified by whole-cell BOX-PCR genomic fingerprints. Significant subspecies heterogeneity in interfacial behavior was revealed. Motility, measured by a soft agar assay, had a very broad range among the E. coli population and was positively correlated with biofilm-forming in minimal medium (MM, r = 0.619, P < 10−4) but not in Luria broth (LB). More biofilm was formed by agn43+ strains in both MM and LB, with a larger effect in MM. ^ We developed two environmentally relevant growth conditions mimicking intestinal versus external conditions to investigate the phenotypic diversity across a subset of E. coli feedlot isolates in terms of surface characteristics and adhesion behavior. Although no significant difference was observed in zeta potentials, most strains become significantly more hydrophobic and form thicker biofilm on polystyrene microwells under external growth conditions. Furthermore, this enhanced biofilm formation was positive correlated with bacterial surface hydrophobicity (r2 = 0.66), and isolates that exhibited the highest surface hydrophobicity also formed visible clumps. Other than hydrophobicity, motility was determinant in affecting E. coli biofilm formation, with all four non-motile isolates characterized as thin-biofilm formers. The majority (88%) of Ag43+ isolates formed thick biofilms, whereas the majority (75%) of Ag43 isolates formed thin biofilms. ^ Eight isolates were selected for bacterial transport study by conducting operational retention tests (ORT) under conditions that simulate pulse application of a bacterial load followed by rainfall infiltration and then natural drainage. Flagella-mediated motility was an important variant in cell retardation for all tested materials; bacterial hydrophobicity was important on Pyrax ® and dolomite; Ag43 expression was important on glass and dolomite. A significant variability in bacterial transport was observed across the E. coli isolates collection. The foodborne pathogen E. coli O157:H7 retained the least with all examined matrices; E. coli K-12 displayed moderate adhesion and may not be a proper model strain to predict E. coli transport. Overall, external growth conditions enhanced bacterial adhesion to all materials, and Pyrax® might serve as a good candidate biobarrier material given its superior removal ability. ^