*2.3. Exposure of Salmonella spp. Contaminated Eggshells to Radiant Catalytic Ionization and Ozonation*

The eggs contaminated with bacterial suspension were placed on a wire stand (which allowed the device to operate evenly on the egg) at a distance of 0.5 m from Induct 750 ActiveTek apparatus (Kielce, Poland) (not generating ozone), Dawid 2 ozonizer (ECS Piotr Paruszewski, Ostrzeszów, Poland) (generating 10 g/h O3) or the fan (control treatment) and exposed for 30 min, 60 min or 120 min to RCI, ozone or the flowing air, respectively. To determine the number of bacteria reisolated from eggshells, eggs were placed in sterile plastic containers with closures filled with 100 mL of sterile saline (Avantor, Gliwice, Poland). Next, they were sonicated (Ultrasonic DU-4 sonicator, Nickel-Electro, Oldmixon, Great Britain) for 5 min and shaken (400 rpm) for 10 min (benchtop shaker). Three nontreated with RCI or ozone eggs allowed determining the initial number of bacteria reisolated after contamination of eggshells with tested suspensions. After sonication, serial 10-fold dilutions in sterile saline for each bacterial suspension obtained after sonication and shaking were prepared. The enumeration was performed on tryptic soy agar (TSA) (bioMerieux). After 24-h incubation at 37 ◦C the number of colonies per egg was calculated (log CFU/egg) (Figure 2). The procedure included three repetitions for each tested strain and each variant.

**Figure 2.** A scheme of experiment procedure.

Decrease in the number of bacteria (DB) (log CFU/egg) after treatment was calculated using the formula: DB = A − B

Where:

A—initial number of bacteria [log CFU/egg];

B—number of bacteria after treatment [log CFU/egg].
