Impact of gas ultrafine bubbles on the efficacy of antimicrobials for eliminating fresh and aged Listeria monocytogenes biofilms on dairy processing surfaces

Ultrafine bubbles (UFB) are a novel concept that has the potential to enhance the potency of antimicrobials to eliminate biofilms. This study investigated the impact of incorporating gas (air, CO2, and N-2) UFB on the potency of chlorine (Cl-2; 50, 100, and 200 ppm) and peracetic acid (PAA; 20, 40, and 80 ppm) antimicrobial (AM) solutions against fresh (3 days) and aged (30 days) Listeria monocytogenes biofilms on polypropylene, silicone, and stainless steel surfaces. Listeria monocytogenes biofilms were statically grown on polypropylene, silicone, and stainless steel coupons (7.62 x 2.54 cm) at 25 degrees C for 3 or 30 days, by immersing in a three-strain cocktail of L. monocytogenes in brain heart infusion (BHI) broth. The coupons were treated by submerging in AM solutions with or without UFB for 1 min, then swabbed into Dey-Engley neutralizing broth and enumerated on BHI agar. Incorporation of air, CO2, and N-2 UFB in AM solutions resulted in significantly increased log reductions (0.4-1.5 logs) of fresh and aged L. monocytogenes biofilms on polypropylene and stainless steel surfaces, whereas incorporation of CO2 UFB in AM solutions resulted in similar to 1 log greater reductions of fresh and aged L. monocytogenes biofilms on silicone surfaces compared with AM solutions without UFB. This study also demonstrated that 200 ppm Cl-2 was most effective against fresh and aged L. monocytogenes biofilms on polypropylene, silicone, and stainless steel surfaces compared with 50 ppm Cl-2, 20 ppm PAA, and 40 ppm PAA.