PCR-based Quality Control of Listeria spp. and L. monocytogenes in Ready-To-Eat Salads Sold in Italy

A total of 48 samples of ready to-eat salads (RTE), containing different varieties of salads, of different brands sold in Italy, were purchased from several supermarkets, during period 2008-2009. This study was performed to determine whether microbial contamination, and in particular pathogenic bacteria, such as Listeria monocytogenes, were present in these food products. Samples were examined for mesophilic aerobic counts, yeasts and moulds, total and fecal coliforms, and presumptive Listeria monocytogenes counts. Results showed that, in general, the highest microorganism counts were associated with samples containing grated carrot (6.3 Log cfu g-1 of aerobic mesophilic microorganisms; 4.6 Log cfu g-1 of yeast and moulds; 2.8 Log cfu g-1 of total coliforms), while the lowest counts were, generally, associated with samples containing lettuce (2.8 Log cfu g-1 of aerobic mesophilic microorganisms; 2.3 Log cfu g-1 of yeast and moulds; 2.3 Log cfu g-1 of total coliforms). Of all the samples analyzed, only three (6 %) harboured L. monocytogenes.