Specific detection of Listeria monocytogenes and Listeria spp. in vacuum-packed smoked and graved salmon via chromogenic media and VIT Listeria gene probe

The objective of our study was to assess the application of specific gene-probes (VIT-Listeria system) and two chromogenic media ALOA- and RAPID'L. mono-agar for the detection of Listeria monocytogenes and Listeria spp. in 30 commercial samples of vacuum-packed salmon. The official method according to 35 LMBG (German food act) served as a reference procedure. The evaluation of the VIT-test took place under the epifluorescence microscope. After stimulation with a high energetic light the bacteria began to shine: Listeria lit up green, Listeria monocytogenes both green and red. On the negative-control field bacteria shone neither red nor green. Using the official reference procedure 15 (50%) of the 30 samples studied could be identified as Listeria positive and were also confirmed positive by the VIT system. Using the alternative method with chromogenic media and VIT system 16 (53,3%) samples could be identified as Listeria positive. 13 samples (reference procedure) and 14 samples (alternaive method) were positive for L. monocytogenes. None of the samples showed a false positive or false negative result. The VIT Test demonstrated a very good sensitivity and a specificity of 100%.