Evaluation of an enumeration method for Listeria monocytogenes at low contamination levels in cold-smoked salmon

For the enumeration of Listeria monocytogenes in cold-smoked salmon, a sensitive enumeration method, based on membrane filtration followed by transfer of the filter on a selective medium has been recently developed (Gnanou Besse et al., 2004, A contribution to the improvement of L. monocytogenes enumeration in cold-smoked salmon. International Journal of Food Microbiology, 91, 119–127). The aim of the study was to assess the performance of this enumeration method through an inter-laboratory study, using cold-smoked salmon artificially contaminated at 2 different levels (approximately 0.6 and 1.6 log 10 CFU g − 1 ). A reproducibility standard deviation of 0.23 log 10 CFU g − 1 and 0.15 log 10 CFU g − 1 was obtained for the method respectively at the lower level and the higher level. Under certain conditions, the uncertainty of measurement can be derived from the method reproducibility standard deviation and was calculated to be 0.46 log 10 CFU g − 1 for the lower contamination level and 0.30 log 10 CFU g − 1 for the higher contamination level. These values can be considered as satisfactory for such low contamination levels.