Adherence kinetics, resistance to benzalkonium chloride and microscopic analysis of mixed biofilms formed by Listeria monocytogenes and Pseudomonas putida

Comparison between the resistance to BAC and the microscopic structure between mixed-species biofilms formed by different strains of Listeria monocytogenes and Pseudomonas putida CECT 845 under different scenarios and that obtained by the corresponding monospecies L. monocytogenes biofilm was carried out. The association of P. putida with L. monocytogenes quickens biofilm formation and increases significantly (p < 0.05) the BAC-resistance of the biofilm after 4 days of incubation at 25 °C respecting to that formed by monospecies biofilms. According with the adherence profiles of P. putida, two different patterns of association between both species (A and B) were identified, being type A pattern found in the mixed biofilms much more resistant to BAC. After 11 days of incubation, a destructuration of mixed biofilms occurred in all experimental assays, being in 2 out of 5 experimental cases (4032 and BAC-adapted 5873 on polypropylene) accompanied by a sharp decrease in the number of adhered cells. Microscopic analyses demonstrated that complex three-dimensional microscopic structure showed the highest resistance to BAC (4032-SS). Obtained results clearly highlight that to improve disinfection protocols for assuring food safety, it is necessary to mimick those bacterial association that occur in nature