Purpose: The RAPID and iQ-Check ranges of products provide effective methods for the detection of Listeria species. They are based on an enrichment step in Half-Fraser broth or Listeria Special Broth and subsequent detection on a chromogenic or with real-time PCR. A study was conducted to verify the ability of these methods to properly detect the new Listeria species.
Methods: The growth of heat stress cells in LSB and Half-Fraser broth was checked in a bioscreen or by spotting the cultures on TSA. Recovery rates of the chromogenic media were calculated using TSA as the non-selective medium and were compared to those obtained with PALCAM reference agar. The color of the colonies produced on each medium was recorded. An inclusivity/exclusivity study was performed with the PCR kits.
Results: It was demonstrated that LSB was superior for recovery of stress cells. Listeria rocourtiae DSM22097, Listeria marthii DSM23813 and Listeria fleischmannii DSM24998 was detected on all chromogenic media after 24 hours of incubation with a recovery rate > 0.5. Listeria weihenstephanensis DSM24698 needed 48 hours to grow. The four strains developed typical colonies of Listeria spp. on each medium. In comparison, Listeria rocourtiae DSM22097 and Listeria weihenstephanensis DSM24698 were unable to cultivate on PALCAM reference agar. Positive results were obtained with iQ-Check Listeria spp. while the iQ-Check Listeria monocytogenes tests were negative.
Significance: Currently existing methods for the detection of Listeria spp. such are suitable for the detection of the new strains Listeria rocourtiae, Listeria marthii, Listeria weihenstephanensis and Listeria fleischmannii.