Purpose: To evaluate the disinfectant activity of inadequate concentrations of Benzalkonium chloride against bacterial biofilms.
Methods: In the context of ProSafeBeef EU project, mixed culture biofilms were formed on stainless steel surfaces in the combinations of L. monocytogenes (3 strains), P. putida (3 strains) and L. sakei (3 strains). The disinfection efficiency of Benzalkonium chloride(20, 50, 100, and 200 ppm) was evaluated by detaching the remaining viable biofilm cells and enumerating by agar plating. The experiment lasted 10 days in total. Additionally, stainless steel surfaces exposed daily to disinfectant solutions and were tested for the recovering cells after their transfer to new medium.
Results: The population of P. putida was benefited by the presence of L. monocytogenes, and L. sakei, while the levels of 20, 50, and 100 ppm of the disinfectant were insufficient to suppress the biofilm populations and its efficiency was completely decreased as time elapsed. It is evident that after the 4th day of the experiment, the log reduction of microorganisms population after the disinfection ranged from 0 to 1 log CFU/g in all cases of mixed biofilms.
Significance: Such studies demonstrate the increased resistance of biofilms to common disinfectants, as well as the necessity of using the correct quantities for the complete elimination of the remaining biofilm cells.