2.3. Time‐kill assay

To determine the time at which formaldehyde exerts its antibacterial effect on S. aureus, whether permethrin delays bacterial growth and whether permethrin interferes with the effect that formaldehyde exerts against S. aureus, a time‐kill assay was conducted. The bacterial inoculum was set up as was done for the combined exposure experiment described above and samples incubated on a benchtop orbital shaker at 35°C and 100 rpm. At 0, 4, 8, and 24 hr postincubation, samples were taken and viable counts determined as described in Section 2.4. Each experiment was repeated three times independently.