A Combined Modified Reverse Dot-blot and Nested PCR Assay for the Specific Non-radioactive Detection of Listeria Monocytogenes

A modified reverse dot-blot assay was developed and used in combination with a nested PCR amplification of hly A for the specific detection of Listeria monocytogenes. The deoxynucleotides and digoxygenin-11-dUTP concentrations in the PCR were optimized for maximal sensitivity and economy. For the dot-blot hybridization, digoxygenin-labelled PCR products were directly spotted on nylon membrane-bound poly-dT tailed capture probes and the signal detection was either colorimetric or chemiluminescent. With crude cell lysates, the total assay could be completed in about 6 h with a detection limit between 2 and 25 colony forming units (cfu) per PCR. The assay was then tested for its applicability to environmental sampling of artificially contaminated aluminum surfaces. For environmental sampling, the assay requires an additional overnight enrichment step and has a sensitivity corresponding to 5 cfu per 25 cm2 of inoculated surface.