Abstract :
[en] A high level of protection of public health is one of the fundamental objectives of European food laws, as laid down in Regulation (EC) No 2073/2005. Listeria monocytogenes is a pathogen found within the food-processing industries, mainly brought by human, and was responsible of 1,381 confirmed cases of foodborne listeriosis for 2008 in Europe. Salmonella was in 2008, the second most often reported zoonotic disease in humans, and 131,468 confirmed cases of human salmonellosis were reported in Europe. The aim of the present work was to develop and to validate a quicker and more sensitive genetic method for quantification of L. monocytogenes and Salmonella spp. in meat products by the quantitative real-time PCR. After preliminary tests for primers and probes choice, the genetic method was validated with classical microbial methods (ISO 11290-2:1998, ISO 6579) using challenge tests. A mixture of 3 strains was realized for each bacterial genus: 1 referee strain (L. monocytogenesT NTCT 11994 or S. TyphimuriumT ATCC 14028) and 2 lab isolates. Experiments were carried out on pork's irradiated and not irradiated minced meat. These meats were packaged either in expanded polystyrene trays wrapped with permeable stretch film or under modified atmosphere (70% O2/30% CO2) in sealed trays. The initial inoculum (102 cfu.g-1) was homogenized in minced meat before packaging in trays. They were incubated for 14 days, at +5, +8 and +10°C and at +10 and +12°C, for respectively L. monocytogenes and Salmonella spp. In the 2 tested meats, growth speeds as well as the final populations increased according to the temperature. In the not irradiated minced meat, growth speeds of the pathogenic flora as well as the associated final populations were lower than those observed in the irradiated matrices. As soon as the total flora reached its stable growth phase, growths of the various pathogenic stagnated. The growth of the original flora inhibited partially the growth of pathogens inoculated. Generally, growth of the total flora is partially inhibited by modified atmosphere packaging. The analytical methods of molecular biology allow faster and less heavy analyses, in terms of hand of work and execution, than the methods of classic microbiology.
