Preparation of disinfectant solutions: The pH 12.0 lethal alkali treatment was prepared by adding 380 [micro]l of 4M NaOH (Fisher Scientific, New Jersey, USA) to 10 ml of TSBYE. The lethal 1000 ppm of [H.sub.2][O.sub.2] (Acros Organics, New jersey, USA) was prepared by adding 800 [micro]l of [H.sub.2][O.sub.2] (1.5%) to 10 ml of TSBYE.
monocytogenes cells in lethal disinfectants and antimicrobials, 1 ml of heat stressed or control cells were added to 9 ml of TSBYE containing disinfectants to yield 7 log CFU/ml.
Each well of (Brand, Wertheim, Germany) was filled with 180 [micro]L of TSBYE and 20 [micro]L of an overnight culture obtained as described above.
Cultures were produced as described previously, but only 0.1 mL of the last inoculum was transferred to 10 mL of TSBYE (1: 100) and further incubated at 37[degrees]C for 18-20 h.
After the exposure to these sublethal stresses, each suspension was harvested by centrifugation (8877 xg, 10 minutes, 4[degrees]C; Rotina 35 R) and the pellet resuspended with 50 mL of TSBYE. From this suspension, 20 [micro]L were added to three wells of sterile polystyrene tissue culture plates containing 180 [micro]L of TSBYE.
Induction of heat stress adaptation: The sublethal heat stress adaptation was performed by adding 1 ml of stationary-phase culture to 9 ml of TSBYE and heating at 48[degrees]C for 1 h.
These essential oils were solubilized by diluting (1:1) in propylene glycol (PGMP Biochemicals LLC, Solon, Ohio) and required concentrations were then prepared in TSBYE as described in Table 2.