Biofilm formation by Staphylococcus aureus on food contact surfaces: Relationship with temperature and cell surface hydrophobicity

Staphylococcus aureus (S.aureus) is a pathogenic bacterium capable of developing biofilms on food processing surfaces, a pathway leading to cross contamination of foods. The purpose of this study was to evaluate the ability of S.aureus to form biofilm on food processing surfaces (polystyrene and stainless steel) with regard to different temperatures (12 and 37°C) and cellular hydrophobicity. Biofilm assays were performed on n. 67 S.aureus isolates from food, food processing environments and food handlers and n. 3 reference strains (S.aureus ATCC 35556, S.aureus ATCC 12600 and S.epidermidis ATCC 12228). A strain-specific variation in biofilm formation within S.aureus strains tested was observed. At 37°C, n. 38/67 (56.7%) of strains were biofilm producer in at least one tested surface. A total of n. 25/38 (65.7%) of strains were biofilm producer on polystyrene whereas n. 24/38 (63.1%) were biofilm producer on stainless steel. Moreover, n. 11/38 (28.9%) of strains were biofilm producers on both selected surfaces. The majority of S.aureus strains which produced biofilms (n. 17/38-44.7%), were isolated from food environments. At 12°C, only one S.aureus strain from food handler (S.aureus 374) was biofilm producer. Cell surface hydrophobicity level increased with temperature. Additionally, a statistically significant difference (P<0.001) was found between hydrophobicity at 37°C and 12°C. Finally, the architecture of biofilm formed by S.aureus strains on polystyrene and stainless steel surfaces at selected temperatures was observed by scanning electron microscopy. The appearance of thick extracellular products in strongly (S.aureus ATCC 35556 - positive control) and the absence of those products in the non-biofilm producer (S.epidermidis ATCC 12228 - negative control) is presented.