Comparing Biofilm Forming Potential of Listeria Species on Non-food and Food-contact Surfaces of Importance to the Dairy Industry

Authors

Hannah Cooper, South Dakota State UniversityFollow

Faculty Mentor

Dr. Sanjeev Anand

Abstract

Listeria monocytogenes (Lm) is a foodborne pathogen of major safety concerns. This bacterium can resist/adapt to environmental stressors and persist through forming robust biofilms despite dairy plants following stringent surface cleaning protocols. Surface roughness is considered a major factor controlling bacterial attachment and biofilm formation. Food contact surfaces like stainless steel (SS) have low surface roughness for easy cleaning. On the other hand, non-contact surfaces like floors need a rougher surface to ensure employee safety. Hence, we hypothesized that Listeria biofilm formation would be lower on stainless steel compared to clay brick (CB; common flooring material in dairy plants). This study used L. innocua (Li; non-pathogenic) as the test strain instead of Lm because of its similar biofilm-forming capacity and isolation from similar environmental settings. Biofilms of Li were developed on SS and CB tiles (2.54x2.54 cm²) using 7-log₁₀CFU/mL Li spiked reconstituted non-fat dry milk (11%w/v; R-NFDM) for 24h at 37°C. The R-NFDM was analyzed for fat, protein, lactose, total solid, solid-not-fat content, and pH. Simultaneously, as a control, biofilm on the tiles was formed using brain heart infusion broth. Biofilm counts were obtained through swabbing. Dilutions were plated on brain heart infusion agar and incubated at 37°C for 24-48h, and counts were expressed as log₁₀CFU/coupon. Three trials in duplicate were completed, with 6 tiles each. Means were compared using a one-way analysis of variance (ANOVA). The biofilm counts for SS were 5.33±0.12, and for CB tiles were 5.54±0.08 (P-value>0.05). The findings demonstrated that both surfaces equally supported biofilm development by Li. Therefore, establishing effective interventions to eliminate Lm biofilms and lower the risk of product cross-contamination is critical.

Recommended Citation

Cooper, Hannah (2023) "Comparing Biofilm Forming Potential of Listeria Species on Non-food and Food-contact Surfaces of Importance to the Dairy Industry," The Journal of Undergraduate Research: Vol. 18, Article 3.
Available at: https://openprairie.sdstate.edu/jur/vol18/iss1/3