Direct detection of Listeria monocytogenes from milk by magnetic based DNA isolation and PCR

Two nucleic acid-based methods for rapid and sensitive detection of the foodborne pathogen Listeria monocytogenes in milk were developed in this study. These methods rely on paramagnetic nanoparticle-based isolation of bacterial DNA directly from milk and subsequent PCR with selective primers for the listeriolysin O (hlyA) gene. The hlyA specific product was reproducibly detected and showed a sensitivity of 10 cfu ml(-1). The magnetic-based system had a sensitivity 10-fold higher than that of commercially available column devices. The detection limit of both methods is sufficient for direct detection of L. monocytogenes DNA in milk avoiding the enrichment culturing step, reducing the time necessary to obtain results from samples to 7 h rather than the 5-day minimum required for the standard procedure. The methods developed are suitable for automation.