BIOFILM-FORMING ABILITY OF STAPHYLOCOCCUS AUREUS FROM FOOD ENVIRONMENT

Staphylococcus aureus (S.aureus) is one of the well known pathogens that can live in a wide variety of environments. It also has an inherent ability to form biofilms on biotic and a-biotic surfaces (1). Biofilm formation is important for survival of S.aureus in the food industry (2). Currently, little is known about the ability of food-related S.aureus strains to form biofilms (3). The aim was to evaluate the biofilm-forming ability of S.aureus on food processing surfaces at 12 and 37◦C. Biofilm assays were performed on n.26 wild isolates. Biofilm was allowed to develop on polystyrene and stainless steel at selected temperatures. After 24-h incubation, the amount of biofilm was determined spectrophotometrically and results expressed as ’Biofilm Production Index’ (BPI) = [O.D.meanbiofilm surface (mm2)-1] x 100. Biofilm was compared with reference strains: S.aureus ATCC 35556 (positive control - BPIPC), S.aureus ATCC 12600 (reference strain - BPI12600) and S.epidermidis ATCC 12228 (negative control - BPINC) for each isolate. All isolates were defined into different categories on the basis of their BPIs values. The cutoff point for the biofilm production was the BPI value obtained by negative control on polystyrene (BPINC = 0.294) and stainless steel (BPINC = 0.149). S.aureus strains showing ability to produce biofilms were classified as weak (BPINC ≤ S.aureus BPIs < BPI12600), moderate (BPI12600 ≥ S.aureus BPIs < BPIPC ) or strong (S.aureus BPIs âL’e BPIPC). Finally, in order to evaluate the architecture ˇ of the biofilms, the SEM analysis was carried out. A strain-specific variation in biofilm formation within S.aureus strains was observed. At 37◦C, n.17/26 (65.3%) of strains were biofilm producer in at least one tested surface. A total of n.13/26 (50%) of strains were biofilm producer on polystyrene whereas n.10/26 (38.4%) were biofilm producer on stainless steel. Moreover, n.6/26 (23%) of strains were biofilm producers on both surfaces. In details, n.2/17 (11.7%) were classified as moderate biofilm producer on polystyrene whereas they were no biofilm producer on stainless steel. At 12Â◦C, all strains were no biofilm producer. Our results suggest that the biofilm formation of S.aureus is influenced by environmental conditions relevant for the food industry. This study attempted to investigate the biofilm formation by wild S.aureus isolates and to correlate the BPI values with the SEM images.