Comparative Evaluation of Different Sanitizers Against Listeria monocytogenes Biofilms on Major Food-Contact Surfaces

Abstract

Contaminated food-contact surfaces are recognized as the primary reason for recent L. monocytogenes outbreaks in caramel apples and cantaloupes, highlighting the significance of cleaning and sanitizing food-contact surfaces to ensure microbial safety of fresh produce. This study evaluated efficacies of four commonly used chemical sanitizers at practical concentrations against L. monocytogenes biofilms on major food-contact surfaces including stainless steel, low-density polyethylene (LDPE), polyvinyl chloride (PVC), polyester (PET), and rubber. In general, efficacies against L. monocytogenes biofilms were enhanced by increasing concentrations of quaternary ammonium compound (QAC), chlorine, and chlorine dioxide, or extending treating time from 1 to 5 min. The 5-min treatments of 400 ppm QAC, 5.0 ppm chlorine dioxide, and 200 ppm chlorine reduced 3.0-3.7, 2.4-2.7, and 2.6-3.8 log₁₀ CFU/coupon L. monocytogenes biofilms depending on surfaces. Peroxyacetic acid (PAA) at 160 and 200 ppm showed similar antimicrobial efficacies against biofilms either at 1- or 5-min contact. The 5-min treatment of 200 ppm PAA caused 4.0-4.5 log₁₀ CFU/coupon reduction of L. monocytogenes biofilms on tested surfaces. Surface material had more impact on the efficacies of QAC and chlorine, less influence on those of PAA and chlorine dioxide, while organic matter soiling impaired sanitizer efficacies against L. monocytogenes biofilms independent of food-contact surfaces. Data from this study provide practical guidance for effective disinfection of food-contact surfaces in food processing/packing facilities.

Keywords: L. monocytogenes; biofilm; food-contact surfaces; organic matter; peroxyacetic acid; sanitizers.

Figure 1

Antimicrobial efficacy of quaternary ammonium compound (QAC) against L. monocytogenes biofilms on food-contact surfaces. (A) Stainless steel (SS); (B) low-density polyethylene (LDPE); (C) polyvinyl chloride (PVC); (D) polyester (PET); (E) rubber. The 7-day-old biofilms on different surface coupons (15 mm × 7.5 mm) were treated with 200 or 400 ppm QAC for 1 or 5 min at 22°C. The surviving bacteria were shown as means ± SEMs, n = 3. ^a–dBars topped with the different letters are significantly different at p ≤ 0.05.

Figure 2

Antimicrobial efficacy of chlorine dioxide against L. monocytogenes biofilms on food-contact surfaces. (A) Stainless steel (SS); (B) low-density polyethylene (LDPE); (C) polyvinyl chloride (PVC); (D) polyester (PET); (E) rubber. The 7-day-old biofilms on different surface coupons (15 mm × 7.5 mm) were treated with 2.5 or 5.0 ppm chlorine dioxide solution for 1 or 5 min at 22°C. The remaining bacteria post-sanitizer treatment were shown as means ± SEMs, n = 3. ^a–dBars topped with the different letters are significantly different at p ≤ 0.05.

Figure 3

Antimicrobial efficacy of chlorine against L. monocytogenes biofilms on food-contact surfaces. (A) Stainless steel (SS); (B) low-density polyethylene (LDPE); (C) polyvinyl chloride (PVC); (D) polyester (PET); (E) rubber. The 7-day-old biofilms on different surface coupons (15 mm × 7.5 mm) were treated with 100 or 200 ppm chlorine solution for 1 or 5 min at 22°C. The survivors post-chlorine treatment were enumerated and shown as means ± SEMs, n = 3. ^a–cBars topped with the different letters are significantly different at p ≤ 0.05.

Figure 4

Antimicrobial efficacy of peroxyacetic acid (PAA) against L. monocytogenes biofilms on food-contact surfaces. (A) Stainless steel (SS); (B) low-density polyethylene (LDPE); (C) polyvinyl chloride (PVC); (D) polyester (PET); (E) rubber. The 7-day-old biofilms on different surface coupons (15 mm × 7.5 mm) were treated with 160 or 200 ppm PAA for 1 or 5 min at 22°C. The surviving bacteria were shown as means ± SEMs, n = 3. ^a,bBars topped with the different letters are significantly different at p ≤ 0.05.

Figure 5

Efficacy of four commonly used sanitizers against L. monocytogenes biofilms on food-contact surfaces conditioned with organic matters. (A) Quaternary ammonium compound (QAC, 400 ppm); (B) chlorine (200 ppm); (C) chlorine dioxide (ClO₂, 5.0 ppm); (D) peroxyacetic acid (PAA, 200 ppm); stainless steel (SS); low-density polyethylene (LDPE); polyester (PET); polyvinyl chloride (PVC). Apple juice: food-contact surfaces were conditioned with apple juice; milk: food-contact surfaces were conditioned with milk. The 7-day-old biofilms on different surface coupons (15 mm × 7.5 mm) were treated with the respective sanitizers for 5 min, then survivors were enumerated and shown as means ± SEMs, n = 3. ^a–cBars topped with the different letters are not significantly different at p ≤ 0.05.