Summary: Lucy Sutton et al. (2025) show that mature biofilms of L. monocytogenes on stainless‐steel surfaces failed to respond to high‐concentration sanitizers.
Sanitizer May Not Always Be Effective Against L.monocytogenes in Biofilms
Why This Matters:
- Ready-to-eat foods and produce are processed with minimal kill-steps post‐harvest, making environmental sanitation of surfaces and equipment vital to controlling L. monocytogenes.
- Traditional sanitation metrics focus on planktonic organisms or early‐stage biofilms; mature biofilms pose a hidden hazard, as they can lead to persistence.
- This study underscores that biofilm age, temperature of growth, surface material, and sanitizer type/concentration influence control efficacy.
- For HACCP plans, understanding that standard sanitizers may underperform against mature biofilms is essential for hazard analysis, critical control point (CCP) design, and verification.
Key Findings: Lucy Sutton et al. (2025) investigated how mature biofilms of L. monocytogenes on stainless‐steel coupons at 20°C and 4°C for one week and how they respond to high‐concentration sanitizers.
- Biofilms grown at 20°C achieved ~8 log₁₀ CFU/cm², whereas those at 4°C reached ~4 log₁₀ CFU/cm², highlighting how temperature influences biofilm accumulation.
- Planktonic cells were eliminated by relatively low concentrations of chlorine (150 ppm) or peracetic acid (200); in contrast, mature biofilms resisted high concentrations (chlorine 300 ppm or PAA 500 ppm) and extended exposure.
- Microscopy revealed biofilms adhering to scratches/troughs in stainless steel, indicating physical surface features contribute to persistence of biofilms.
Bigger Picture: This study shifts the sanitation paradigm from simply achieving microbial log reductions toward managing persistent biofilm reservoirs. For HACCP and sanitation teams:
- Mature L. monocytogenes biofilms on processing surfaces can survive standard sanitizer regimes, especially in cold-chain or low-activity zones.
- Temperature control (keeping surfaces cold) helps limit biofilm formation, but once established, biofilms require enhanced mechanical disruption and targeted sanitization beyond typical planktonic protocols.
- Sanitation verification must not just record surface counts but also monitor biofilm presence, surface integrity, and environmental niches (e.g., scratches, joints, drains) that favour persistence.
- This work supports integrating biofilm risk assessment into HACCP hazard analysis and refining CCPs for fresh food processing environments to account for mature biofilms.
(Image Credit: iStock/z1b)
References:
- Sutton et al. (2025) Mature Listeria monocytogenes Biofilms Exhibit Reduced Susceptibility to Sanitizers - Relevance to the (Leafy Green) Fresh Food Supply Chain. Journal of Food Protection, Vol. 88, Issue 12, 100652.
