Abstract :
[en] Introduction
Listeria monocytogenes is the bacterium responsible for listeriosis, a foodborne disease for which the number of cases increased during the recent years in the European Union (1). Various types of cheese have already been identified as eventual vectors of L. monocytogenes (2). Cheese is considered as suitable for the growth of the pathogen, following Regulation (CE) N°2073/2005, if it presents a pH > 4.4, a water activity > 0.92 or a combination of a pH > 5.0 with a water activity > 0.94 (3). To assess the real growth potential of L. monocytogenes in a panel of 32 artisanal cheeses, challenge-tests were performed.
Materials and Methods
Between July 2018 and January 2019, 32 challenge-tests were performed on Belgian artisanal cheeses, sampled to cover the variability of process met in Belgium (4). Three batches were sampled directly after production for each of the 32 types of cheeses, excepting if theoretical growth potential calculated using the online tool Sym’Previus was ≤ 0. In this case, only one batch was studied. A cocktail of three strains of L. monocytogenes was used to inoculate the cheeses. Samples were stored at 7°C during the two first thirds of shelf life, and were then transferred to 9°C for the remaining third. The growth potential of the bacterium in each product was calculated on the basis of enumerations at beginning and end of shelf life.
Discussion
The results were contrasted between types of cheese. A growth of L. monocytogenes was never observed in fresh cheeses. It seems thus that these products should not represent a danger for food safety. In mold-ripened and smear-ripened soft cheese, the pathogen was able to grow, sometimes for more than 5 log cfu/g. Only one exception was observed, for a Herve cheese, with a decrease of at least 0.5 log cfu/g for each of the three batches. Regarding semi-hard/hard cheeses, the growth of L. monocytogenes was generally not allowed. However, in 3 batches out of 32, a limited growth was observed, always around 1 log cfu/g. Statistical analyses were not able to explain the divergence in the results for this cheese family.
