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

Abstract

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 N2) UFB on the potency of chlorine (Cl2; 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 × 2.54 cm) at 25°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 N2 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 ~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 Cl2 was most effective against fresh and aged L. monocytogenes biofilms on polypropylene, silicone, and stainless steel surfaces compared with 50 ppm Cl2, 20 ppm PAA, and 40 ppm PAA.

Effect of gas ultrafine bubbles on the potency of antimicrobials against Escherichia coliO157:H7 biofilms on various food processing surfaces

“…In previous work by our research group, Singh et al (2021) evaluated the impact of gas UFB [denoted as micro‐nano‐bubbles (MNB)] on the efficacy of commonly used AM in the food industry and demonstrated the incorporation of CO 2 UFB improved the potency of 200 ppm chlorine (Cl 2 ) and 28.4 ppm peracetic acid (PAA) solutions against E. coli O157: H7 and Listeria monocytogenes in growth media compared to these AM solutions without UFB. Similarly, Unger et al (2023) evaluated the impact of UFB on the efficacy of AM against fresh and aged L. monocytogenes biofilms on various processing surfaces and discovered that the incorporation of air, CO 2 , and N 2 UFB in Cl 2 (50, 100, and 200 ppm) and PAA (20, 40, and 80 ppm) AM solutions resulted in significantly increased log reductions of fresh and aged L. monocytogenes biofilms on polypropylene and stainless‐steel surfaces compared with AM solutions without UFB.…”

“…A three‐strain E. coli master inoculum cocktail was then prepared by mixing equal proportions of freshly grown cultures, and biofilm were developed on polypropylene, silicone, and stainless steel coupons (7.62 × 2.54 cm 2 ) through static incubation at 25°C for 3 or 30 days by submerging in 40 mL E. coli inoculated BHI broth (9.44 ± 0.07 log CFU/mL) as described by Unger et al (2023). During biofilm development, 20 mL of inoculated BHI broth was replaced by fresh BHI broth after 36 h or every 5 days of incubation for 3‐ and 30‐day biofilms, respectively.…”

“…The preparation of AM solutions was performed at ambient temperature ($20 C) using the procedures described by Unger et al (2023).…”

“…Food-grade compressed cylinders of CO 2 or N 2 gas and ambient air from the laboratory were used to generate UFB in city tap water (Pullman, WA). As shown in Unger et al (2023), the presence and mean size of UFB produced by this generator was conducted by a third-party laboratory.…”

“…To address this gap and further explore the effectiveness of UFB against biofilms, this study examined the impact of gas (air, CO 2 , and N 2 ) UFB on the effectiveness of Cl 2 (50, 100, and 200 ppm) and PAA (20, 40, and 80 ppm) AM solutions against both fresh (3 day) and aged (30 day) E. coli O157:H7 biofilms on polypropylene, silicone, and stainless-steel surfaces. A three-strain E. coli master inoculum cocktail was then prepared by mixing equal proportions of freshly grown cultures, and biofilm were developed on polypropylene, silicone, and stainless steel coupons (7.62 Â 2.54 cm 2 ) through static incubation at 25 C for 3 or 30 days by submerging in 40 mL E. coli inoculated BHI broth (9.44 ± 0.07 log CFU/mL) as described by Unger et al (2023). During biofilm development, 20 mL of inoculated BHI broth was replaced by fresh BHI broth after 36 h or every 5 days of incubation for 3-and 30-day biofilms, respectively.…”