Removal of Listeria monocytogenes biofilms on stainless steel surfaces through conventional and alternative cleaning solutions

Abstract

Conventional treatments are not effective enough to completely remove Listeria monocytogenes biofilms from surfaces, thus implying the presence of certain persistent bacterial forms. In this study, eleven treatments (i.e. two enzymatic agents applied at two different temperatures and concentrations, two alkaline cleaners and one acid detergent) were used to remove mature L. monocytogenes S2-bac biofilms. A combined treatment was then selected for its application to four different L. monocytogenes strains (i.e. CECT 5672, CECT 935, S2-bac, EDG-e). Effectivity of the treatments was evaluated quantitatively using TEMPO and qualitatively by direct epifluorescent microscopy (DEM). Bacterial detachment obtained after the application of acid, alkaline and chlorinated alkaline treatments were 6.03, 6.24 and 4.76 Log CFU/cm2, respectively. Enzymatic treatments applied at 50 °C obtained the greatest detachment and biocidal activity. The results derived from the observation of the remaining biofilm structure by DEM proved that conventional treatments were unable to completely remove conformed structures with the potential risk this entails. Last, the application of a combined treatment using a chlorinated alkaline cleaner followed by an enzymatic treatment enhanced the dispersal of the bacterial cells from surfaces, thus consolidating this as a good option to recommend for the 5-step cleaning procedure.