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

Biofilm formation of Listeria monocytogenes on stainless steel, a widely used abiotic surface in the food processing industry, was investigated by 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 whether there are finishes with significantly lower bacterial attachment. Surface roughness data (measured via four roughness parameters), determined by interferometry, was also compared with the number of adhering cells to detect possible correlations. Cultivation of L. monocytogenes biofilms was carried out using a CDC biofilm reactor with 1% tryptic soy broth set at 20°C for 4, 8, and 24 h. In addition, a cultivation trial was run with continuous nutrient flow (1% tryptic soy broth, 6.2 mL/min) for 24 h. Eight-hour results showed a significant difference (P < 0.05) in biofilm cell counts in biofilms between the glass bead-blasted surfaces (3.23 and 3.26 log CFU/cm2 for the fine and rough, respectively) and deburred (Timesaver) surface (2.57 log CFU/cm2), between drum deburred and deburred (Timesaver) surface (3.41 versus 2.57 log CFU/cm2), and between drum deburred and pickled surface (3.41 versus 2.77 log CFU/cm2). Data gained after 4-h, 24-h, and 24-h plus an 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 four incubation times, suggesting that roughness values, at these ranges, are insufficient in determining the surfaces' affinity to bacteria. Overall, this study suggests that roughness values cannot be used to predict the degree of L. monocytogenes attachment to a specific stainless steel surface.