| Summary: | Among food-borne pathogens, <i>Listeria monocytogenes</i> continues to pose concerns to food business operators due to its capacity to form biofilm in processing environments. Ozone may be an eco-friendly technology to control microbial contaminations, but data concerning its effect on <i>Listeria monocytogenes</i> biofilm are still limited. In this study, the effect of gaseous ozone at 50 ppm on planktonic cells and biofilm of reference and food-related <i>Listeria monocytogenes</i> strains was evaluated. Ozone caused a reduction in microbial loads of 3.7 ± 0.4 and 3.9 ± 0.4 Log10 CFU/mL after 10 and 30 min, respectively. A complete inactivation of planktonic cells after 6 h of treatment was observed. Biofilm inhibition and eradication treatments (50 ppm, 6 h) resulted in a significant decrease of the biofilm biomass for 59% of the strains tested, whilst a slight dampening of live cell loads in the biofilm state was observed. In conclusion, gaseous ozone is not sufficient to completely counteract <i>Listeria monocytogenes</i> biofilm, but it may be useful as an additional tool to contrast <i>Listeria monocytogenes</i> free-living cells and to improve the existing sanitization procedures in food processing environments.
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