Assessing the Formation and Removal of Biofilms of Listeria spp. Isolated on Equipment and Utensils of Dairy Industries in Brazil and Italy

Introduction: Currently, Listeria (L.) monocytogenes is one of the most important foodborne pathogens worldwide because it is an environmental psychrotrophic microorganism with very low infectious dose, able to cause high mortality rates. In addition, Listeria can form biofilms on surfaces that come in contact with food, resulting in food contamination.

Purpose: This study aimed to investigate the presence of Listeria spp. on equipment and utensils of dairy industries, and to investigate the formation and removal of biofilms formed by isolated microorganisms.

Methods: A total of 106 surface samples (100 cm²) were collected in three dairy industries, two located in southern Brazil and one in southern Italy, using the 3M^TM Swab-Sampler. Microorganisms were identified by ISO methods, BAX System (DuPont®) and Kit API Listeria® (BioMérieux). Isolated microorganisms were placed on AISI 316 stainless steel and polyethylene coupons, in order to evaluate the formation and removal of biofilms by different disinfectants. Statistical analyses were carried out using ANOVA, Tukey Test and t-Test.

Results: Seven samples were positive for Listeria spp., being 6 L. innocua and 1 L. monocytogenes. A bacterial pool formed by isolated strains was able to form biofilms of 4.34, 4.33, 4.40 and 4.43 log CFU/cm² on stainless steel coupons, and of 4.44, 4.40, 4.60 and 5.31 log CFU/cm² on polyethylene coupons, in time intervals of 15, 45, 90 and 180 minutes, respectively. The sanitizers 1% Peracetic Acid, 1% Sodium Hypochlorite and 2% Alkyl Dimethyl Benzyl Ammonium Chloride were able to completely inactive the biofilms after 1 and 10 minutes of exposure, demonstrating to be effective against Listeria tested.

Significance: Listeria spp. isolated from dairy industries are able to form biofilms on equipment and utensils, however proper use of sanitizers can eliminate these microorganisms.