Detection of heat injury in Listeria monocytogenes Scott A

Methods of detecting live pathogens in foods that may be growth inhibited f ollowing heat treatment are essential to food safety. Among the techniques available, reverse transcription polymerase chain reaction (RT-PCR) amplifi cation of messenger RNA from heat-injured Listeria monocytogenes Scott A is preferable to direct PCR in an attempt to avoid false positives from dead cells. The RT-PCR has a detection limit of 3 X 10(6) CFU/g, compared to 3 C FU/g for untreated controls, but may not be suitable for the identification of all viable cells. Physically apparent changes in cellular structures fr om heat injury in L monocytogenes are expected to result. Ultrastructural a nalyses did depict notable heat damage as cytoplasmic clearing after 5 min at 60 degreesC. The heat-injured survivors can be readily distinguished fro m total viable cells using selective media. As a result, combinations of mo lecular and visual methods including selective media improve detectability of heat-injured, viable L. monocytogenes Scott A.