EVALUATION OF BIOFILM RESISTANCE ON STAINLESS STEEL SURFACES AND STUDY OF THEIR ADAPTABILITY AFTER THE USE OF INADEQUATE DISINFECTANT SOLUTIONS

摘要

Biofilm formation is a natural phenomenon which occurred on industrial surfaces, most of the times undesirable because of the possible detachment of the bacterial cells, structuring the biofilms community, and the further contamination of the food products. In the current study, mixed culture biofilms were formed by Listeria monocytogenes, Pseudomonas putida and Lactobacillus sakei on stainless steel surfaces. The combinations of mixed culture biofilms were L. monocytogenes (3 strains) - Ps. putida (3 strains) and Ps. putida (3 strains) - Lb. sakei (3 strains). The aim of the study was to evaluate the disinfectant activity of inadequate quantity of Benzalkonium chloride (20 ppm), which is commonly used by food industries for surface sanitation, against bacterial biofilms. The disinfection efficiency was evaluated by detaching the remaining viable biofilm cells and enumerating them by agar plating, as well as by automated conductance measurements (using Rapid Automated Bacterial Impedance Technique). The experiment lasted 10 days in total. During this period, stainless steel surfaces were sampled daily before and after the disinfection (the surfaces were exposed for 6 minutes to the disinfectant solution). In parallel, the rest surfaces (for the samplings of the next days) were also exposed for 6 minutes to the disinfectant solution and then transferred to new medium under aseptic conditions, followed by incubation of remaining biofilm at 18°C. The same procedure was taken place the next day. According to the results, the population of Ps. putida was benefited by the presence of L monocytogenes, and Lb. sakei, while the quantity of the disinfectant was insufficient to kill the biofilm populations and its efficiency was completely decreased with the passage of the days. It is evident that after the 4th day of the experiment and until the end, the log reduction of microorganism population after the disinfection was ranged from 0 to 1 log cfu/cm~2. Such studies demonstrate the increased resistance of biofilms to common disinfectants as well as the necessity to use the correct quantity of disinfectant for the complete killing of the remaining cells of biofilms.