Confirmation of Listeria monocytogenes using a commercially available nucleic acid probe

Abstract

A commercially available nucleic acid hybridization probe for the confirmation of Listeria monocytogenes from selective agar was evaluated. The probe was highly specific and sensitive enough to detect approximately 106 L. monocytogenes per ml in pure culture, forming a very rapid confirmation system. The possibility of using the probe as a direct test from food enrichment broths was explored. Three enrichment protocols using the USDA and FDA methods and PALCAM media were used with three inoculated food types (brie, pâte and raw chicken). The probe was used to test the enrichment broths directly. Uninoculated foods (raw chicken and raw pork) were tested in the same way. The results showed the probe to have great potential as a direct test during enrichment, but its ability to detect the target organism was largely dependent on the food type and the enrichment procedure used. Consequently, there is not one protocol out of the three tested which, when used with the gene probe, could detect all positive samples of each type of food.