Influence of Different Stainless-Steel Finishes on Biofilm Formation by Listeria monocytogenes

Biofilm formation of L. monocytogenes on stainless steel, a widely used abiotic surface in the food processing industry was investigated, focusing on the attachment tendency and behavior of L. monocytogenes 08-5578 on eight different Stainless-steel surfaces: glass bead blasted (rough and fine), deburred (Timesaver), drum deburred, pickled, pickled and drum polished, electrolytic polished and cold rolled (untreated control). The aim was to see if there are finishes with significant lower bacterial attachment. Roughness properties (Ra, Rt, Rz, RSm; determined by interferometry) were also compared with number of adhering cells to detect possible correlations. Cultivation of L. monocytogenes biofilms was carried out using a CDC biofilm reactor (CBR) with 1% TSB set at 20°C for 4, 8, and 24 h. Additionally, a cultivation trial was run with continuous nutrient flow (1% TSB, 6.2 ml/min) for 24 h. Eight hour results showed significant difference ( P < 0.05) in biofilm cell counts in biofilms between the glass bead blasted surfaces (3.23 and 3.26 log CFU/cm 2 for the fine and rough, respectively) and deburred (Timesaver) surface (2.57 log CFU/cm 2 ); between drum deburred and deburred (Timesaver) surface (3.41 vs 2.57 log CFU/cm 2 ); between drum deburred and pickled surface (3.41 vs 2.77 log CFU/cm 2 ). Data gained after 4, 24 h and the additional 24 h continuous flow cultivation showed no significant difference in attachment among surfaces. No correlation between roughness data and attachment was found after all 4 incubation times, suggesting that roughness values, at these ranges, are insufficient in determining surfaces’ affinity to bacteria. This study suggests that roughness values cannot be used to predict the degree of L. monocytogenes attachment to a specific stainless steel surface.