Detection of heat injury in Listeria monocytogenes Scott A

Abstract

Methods of detecting live pathogens in foods that may be growth inhibited following heat treatment are essential to food safety. Among the techniques available, reverse transcription polymerase chain reaction (RT-PCR) amplification 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 × 106 CFU/g, compared to 3 CFU/g for untreated controls, but may not be suitable for the identification of all viable cells. Physically apparent changes in cellular structures from heat injury in L. monocytogenes are expected to result. Ultrastructural analyses did depict notable heat damage as cytoplasmic clearing after 5 min at 60°C. The heat-injured survivors can be readily distinguished from total viable cells using selective media. As a result, combinations of molecular and visual methods including selective media improve detectability of heat-injured, viable L. monocytogenes Scott A.