Evaluation of thin agar layer method for recovery of heat-injured foodborne pathogens

The Thin Agar Layer /TAL) method of Kang and Fung 1998 was used to enumerate heat-injured (55 degreesC for 10 min) foodborne pathogens. This method involves overlaying 14 mL, of nonselective medium (Tryptic Soy Agar, TSA) onto a prepoured, pathogen-specific, selective medium. The recovery rate with the TAL method was compared with the rate for TSA and pathogen-specific, selective media. No significant differences occurred between TSA and TAL (P > 0.05) for enumeration of heat-injured Escherichia coli O157:H7, Listeria monocytogenes, Salmonella typhimurium, Staphylococcus aureus, and Yersinia enterocolitica, and both recovered significantly higher numbers than selective media (P < 0.05). The TAL method is a 1-step, convenient procedure for recovery of heat-injured cells.