1.1 Bacterial strains and growth conditions

The bacterial strains used in this study were the E. coli parental strain AJW678, which was characterized as an efficient biofilm former (Kumari et al., 2000) and its isogenic flhD, fliA, fimA, and fimH mutants. The flhD mutant was constructed by P1 transduction, using MC1000 flhD:kan (Malakooti, 1989) as a donor and AJW678 as a recipient. This resulted in strain BP1094. AJW2145 contained a fliA::Tn5 insertion, AJW2063 a fimA::Kn mutation, and AJW2061 a fimH::kn mutation, all in AJW678 (Wolfe et al., 2003). The mutations abolish expression of FlhD/FlhC, FliA, FimA, and FimH, respectively. As a consequence, mutants in flhD and fliA are non-motile, whereas mutants in fimA are lacking the major structural subunit and mutants in fimH the mannose specific adhesive tip of the type I fimbrium. Bacterial strains were stored at -80°C in 8% dimethylsulfoxide, plated onto Luria Bertani plates (LB; 1% tryptone, 0.5% yeast extract, 0.5% NaCl, 1.5% agar) prior to use, and incubated overnight at 37°C. Bacterial strains are summarized in Table 2.