Purpose: To evaluate the transfer of bacterial biofilm cells in comparison with that of planktonic cells of E. coli O157:H7, Salmonella enterica ser. Typhimurium and Listeria monocytogenes to beef filets.
Methods: In the context of ProSafeBeef, an EU-funded project six sequential, non-inoculated beef filets came in contact with stainless steel surfaces where each of E. coli O157:H7 (3 strains), Salmonella enterica (3 strains) and L. monocytogenes (6 strains) had previously formed biofilm. In parallel, six sequential, non-inoculated beef filets came in contact with stainless steel surfaces contaminated by planktonic cells of each pathogen at the same levels as with biofilm cells. The time of contact between filets and surfaces was 1 or 15 min, respectively, and each experiment was replicated twice (2 batches) with three samples analyzed each time.
Results: All non-inoculated beef filets were contaminated through their contact with the stainless steel surfaces with biofilm or planktonic cells for all pathogens, regardless of contact time. The stainless steel surfaces with biofilm of Salmonella, for 1 minute time of contact, contaminated all samples with the sixth sample to be at the level of 4.12 log CFU/cm2 while the corresponding population with planktonic cells was 2.95 log CFU/cm2. In this respect, the population of E. coli O157:H7 in the case of biofilm and planktonic cells for the sixth sample was 2.34 log CFU/cm2 and 0.45 log CFU/cm2, respectively. For 15 min time of contact, L.monocytogenes biofilm cells contaminated the beef in higher numbers for all samples in comparison with planktonic cells.
Significance: The results can be used to fill knowledge gaps in risk assessment studies since they provide significant insights for the risk estimation related to cross-contamination aiming thus to food safety enhancement.