Elimination of mature Listeria monocytogenes biofilms formed on preconditioned and non-preconditioned surfaces after the application of cleaning treatments and their cell regeneration

In the present study, four different L. monocytogenes strains belonging to serotypes 1/2a and 4b were used to determine biofilm formation capacity on preconditioned (i.e., containing a layer of dirt) and non-preconditioned (i.e., hygienic) surfaces. Conventional (i.e., chlorinated alkaline) and alternative (i.e., chlorinated alkaline plus enzymatic) treatments were applied to observe their effectivity in the simulated models. Biofilm regeneration after the application of treatments was also evaluated to understand the potential risks associated with the non-complete elimination of the structures. Results demonstrated that L. monocytogenes formed biofilms in both conditions tested, although their growth depended on the strain, showing higher formation on non-preconditioned surfaces than on preconditioned surfaces (6.63 ± 0.42 and 5.71 ± 0.60 log CFU/cm2 as a mean value for all strains, respectively). The alternative treatment was significantly (P < 0.05) more effective than the conventional one but neither of them eradicated the microorganism completely from the preconditioned and non-preconditioned surfaces. After 24 h of both treatments’ application, biofilm was regenerated to similar counts as the controls. The non-complete elimination of a biofilm structure poses a risk since part of it remains on the surface, increasing the chance of cells regrowing and producing cross-contamination.