Modulation of Fimbriae Expression by Novobiocin

Assays involving the DNA gyrase inhibitor novobiocin (Sigma-Aldrich) were performed as follows: bacteria containing the fimA-lacZ transcriptional fusion were screened for their Lac phenotypes on MacConkey lactose indicator medium as described previously [27 (link)]. Distinctly phase ON (red/Lac⁺) or phase OFF (white/Lac⁻) colonies were used to inoculate 2 ml LB (lysogeny broth) in test tubes and grown overnight. These were used to inoculate 250 ml flasks containing 25 ml of LB. These cultures were grown aerobically at 200 r.p.m. until they reached an optical density of approximately 0.1 at 600 nm. At this point novobiocin (aqueous stock solution 100 mg ml⁻¹) was added to a final concentration of 0, 12.5, 25, 50, 75, or 100 μg ml⁻¹. Cultures were incubated for a further 20 h before sampling to determine the orientation of the fimS switch in the chromosome.