Zinc downregulates both genes related and non-related to virulence but not rpoE. Overnight cultures of single-copy lacZ fusions JLM164 (LEE1−lacZ; A), JLM165 (LEE4−lacZ; B), MCamp (bla−lacZ; C), and CT32 (rpoE−lacZ; D) were spread evenly onto DMEM plates containing 30 mg/ml X-gal. Discs of sterile filter paper were dropped onto the lawn; 15 μl of different concentrations of zinc acetate were placed on each disc (100 mM, 50 mM, 10 mM, 1 mM, 0.1 mM). These plates were grown for approximately 18 hours and then moved to 4°C for 6 hours to develop the blue color. Virulence genes were downregulated in the presence of zinc (A & B), but so was the bla gene encoding β-lactamase (C). In contrast, rpoE was not downregulated in the presence of zinc (D). Also of note is the small (∼1 mm) zone of growth inhibition around the 100 mM and 50 mM discs.