Listeria monocytogenes growth potential in Ricotta salata cheese

"Growth potential of Listeria monocytogenes was assessed in Ricotta salata, a traditional sheep’s whey cheese. 36 Ricotta salata wheels were inoculated with a mixture of three L. monocytogenes strains obtaining an inoculum level of approximately 102 cfu g-1. Samples were analyzed for the detection and enumeration of L. monocytogenes after 6 h, and after 2, 4 and 6 months. Growth potential (log10 cfu g-1) was 4.87, 6.90 and 6.20 at 2, 4 and 6 months, respectively. The greater relative rate of increase in L. monocytogenes levels was obtained in the first 2 months after inoculation. Ricotta salata supports the growth of L. monocytogenes to levels that may represent a serious risk to public health even during storage at refrigeration temperatures. Further research is needed to assess the effectiveness of postlethality treatments to reduce the initial level of contamination or of competitive microflora to limit the extent of pathogen growth."