Introduction: Biofilms formed by hygienically relevant bacteria on food-contact surfaces present a significant challenge in the food industry, as they have been known to persist despite standard cleaning and disinfection procedures, potentially resulting in recurring food contamination. It is understood that there are limitations of chemical disinfectants and increasingly strict environmental requirements. In this context, plasma is considered a promising alternative, as it enables efficient microbial inactivation at low temperatures while avoiding the use of aggressive chemicals. Purpose: The aim of this master’s thesis was to undertake an evaluation of the effectiveness of plasma in relation to the disinfection of S. enterica Typhimurium, L. monocytogenes, and E. coli biofilms on stainless-steel coupons of different surface roughness, and under different exposure times. Methods: Plasma efficacy was investigated on 24-hour mono-species and mixed-species biofilms of S. Typhimurium, L. monocytogenes, and E. coli grown on non-polished and polished stainless-steel coupons after 1 and 5 min of plasma exposure. Surface properties were characterized by roughness and contact angle measurements. Plasma effects were assessed by colony counting, inhibition-zone measurements, metabolic activity, total biofilm biomass, oxidative stress, and SEM-based morphological analysis. Results: Plasma caused a statistically significant, time-dependent reduction in colony counts in all biofilms, with higher efficacy after 5 min than after 1 min of exposure. L. monocytogenes was inactivated to the detection limit already after 1 min (5,6 log reduction in mono-species biofilms and 7,4–7,6 log reduction in mixed biofilms). E. coli achieved high reductions (>5 log) after 5 min, while S. Typhimurium was the most tolerant species (2,2–3,2 log reduction in mono-species biofilms and 2,6–3,9 log reduction in mixed biofilms). Plasma decreased metabolic activity and increased intracellular oxidative stress, although total biofilm biomass was not significantly reduced. The influence of surface type on efficacy was not pronounced. Discussion and conclusion: Plasma appeared to be an effective supplementary technology for biofilm inactivation on stainless steel, with exposure time being a crucial factor, and the response depended on the bacterial species. The presence of multiple bacterial species in mixed biofilms did not result in an overall increase in tolerance. Since total biomass was not substantially reduced, the results indicate predominantly bactericidal activity without efficient EPS removal. Therefore, practical application is most appropriate in combination with mechanical cleaning procedures in the food industry, with additional validation under conditions of realistic organic load.
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