Evaluation of a chemiluminescent DNA probe assay for the rapid confirmation of Listeria monocytogenes.

A Listeria monocytogenes-specific, acridinium-ester-labelled DNA probe was evaluated in a chemiluminescent homogeneous protection assay (HPA) for the rapid confirmation of suspect L. monocytogenes colonies from blood agar plates. The HPA uses an acridinium-ester-labelled chemiluminescent DNA probe in a free-solution hybridization format. After the DNA probe hybridized with the target ribosomal RNA, the acridinium label on the unhybridized probe was inactivated by a chemical differential hydrolysis step. Formation of a hybrid between probe and target was detected in a luminometer after the addition of a detection reagent. The assay can be completed in 30 to 45 min and allows for simultaneous processing of several (50-100) samples. The probe showed 100% sensitivity and 100% specificity for L. monocytogenes when evaluated in the HPA against L. monocytogenes, other Listeria species and other Gram-positive bacteria. The lower detection limit of the HPA was between 10(4) and 10(5) cells. In an evaluation with 296 bacterial colonies isolated from food, the HPA colony confirmation showed 100% agreement with conventional biochemical characterization. HPA will be useful for the rapid confirmation of L. monocytogenes isolated from food and clinical specimens.