Biofilms of E. coli O157:H7 were produced on wooden coupons in
M9 medium at 22 °C for 3 days, as described above. Coupons were
rinsed in 500 ml of distilled water for 5 s, immersed in 30 ml of sterile
water, NaOCl (200 μg/ml), or ClO2 (200 μg/ml) solutions in 50-ml centrifuge
tubes for 10 min, and rinsed twice in sterile distilled water
(30 ml) to remove residual sanitizers. The coupons were transferred,
without contact with saturated salt solution, to 50-ml centrifuge tubes
in which the RH had been adjusted to 43%. The caps were firmly closed
and tubes were incubated at 22 °C for 1, 3, 6, 9, and 12 h. At each sampling
time, the number of viable E. coli O157:H7 on wooden coupons
was determined as described above.