Inactivation and sublethal injury of foodborne pathogens by high pressure processing: Evaluation with conventional media and thin agar layer method

Abstract

The recovery of seven pathogens was determined in tryptone soya agar (TSA), selective medium and with the thin agar layer (TAL) method, to evaluate inactivation and sublethal injury caused by high pressure at 20 °C. The TAL method consists of selective medium overlaid with TSA. Cell suspensions were treated by combining different pressures (100-MPa increments) and times (1 and 5 min), until complete inactivation. Vibrio parahaemolyticus and Bacillus cereus were totally inactivated at 300 MPa for 5 min and 400 MPa for 1 min; Salmonella typhimurium, Escherichia coli and Yersinia enterocolitica, at 400 MPa for 1 min; and Listeria monocytogenes, at 400 MPa for 5 min and 500 MPa for 1 min. Staphylococcus aureus was the most resistant, being totally inactivated at 700 and 800 MPa for 5 min and 900 MPa for 1 min. Regarding recovery of injured cells, in most cases, counts on the three media were not different. The TAL method may allow differentiation of pathogens from background microbiota of foods.