Detection of Virulence Genes and Growth Potential in Listeria monocytogenes Strains Isolated from Ricotta Salata Cheese

Abstract

Ricotta Salata is a traditional ripened and salted whey cheese made in Sardinia (Italy) from sheep's milk. This product is catalogued as ready-to-eat food (RTE) since it is not submitted to any further treatment before consumption. Thus, foodborne pathogens, such as Listeria monocytogenes, can represent a health risk for consumers. In September 2012, the FDA ordered the recall of several batches of Ricotta Salata imported from Italy linked to 22 cases of Listeriosis in the United States. This study was aimed at evaluating the presence and virulence properties of L. monocytogenes in 87 samples of Ricotta Salata produced in Sardinia. The ability of this product to support its growth under foreseen packing and storing conditions was also evaluated in 252 samples. Of the 87 samples 17.2% were positive for the presence of L. monocytogenes with an average concentration of 2.2 log10 cfu/g. All virulence-associated genes (prfA, rrn, hlyA, actA, inlA, inlB, iap, plcA, and plcB) were detected in only one isolated strain. The Ricotta Salata samples were artificially inoculated and growth potential (δ) was assessed over a period of 3 mo. The value of the growth potential was always >0.5 log10 cfu/g under foreseen packing and storing conditions. This study indicates that Ricotta Salata supports the L. monocytogenes growth to levels that may present a serious risk to public health, even while stored at refrigeration temperatures.

Characterization of antibiogram fingerprints in Listeria monocytogenes recovered from irrigation water and agricultural soil samples

“…In this study, plcA and iap which code for phospholipase and invasion-associated protein respectively, occurred in 100% of the isolates. This is also higher than the prevalence noticed in other studies [53,[55][56][57]. The variations in the prevalence of virulence markers detected in this study and that observed in other studies may be due to the differences in the origin or source of the isolates.…”

Prevalence of Listeria Species in Dairy Cows and Pregnant Women with Reference to Virulotyping of Listeria monocytogenes in Egypt

“…In previous studies, Khedr et al [39] detected inlA and inlB genes in 100% and 75% of examined L. monocytogenes isolates, respectively. However, Coroneo et al [57] recorded inlA and inlB genes in 60% and 47% of L. monocytogenes strains recovered from Ricotta salata cheese, respectively.…”

“…The differences in the distribution of virulence internalin genes could be attributed to the source of samples or L. monocytogenes serotype or mutations in these genes resulted in reduction in invasion or virulence in animal model studies or tissue culture, assuring the significant role of such genes in the pathogenesis and virulence of L. monocytogenes [57][58][59]. It was noticed that 12 isolates of L. monocytogenes carry inlA gene and 6 isolates carry inlB gene that indicates virulent strains of L. monocytogenes and creates hazard in dairy farms as well as milk handlers, milk consumers and pregnant women.…”

Growth potential of Listeria monocytogenes in ready‐to‐eat Feta cheese‐based sauce stored at 4°C

“…Several recent studies have focused on the growth potential of L. monocytogenes in different RTE food products (Awaiwanont, Smulders, & Paulsen, 2015;Coroneo et al, 2016;Dalzini et al, 2014;Grassi, Nucera, Lomonaco, & Civera, 2013;Jesus et al, 2016;Lahou & Uyttendaele, 2017;Michellon et al, 2016;Sahu, Kim, Ferguson, Zink, & Datta, 2017;Sant'Ana, Barbosa, Destro, Landgraf, & Franco, 2012;Skalina & Nikolajeva, 2010;Spanu et al, 2012;Uyttendaele et al, 2009). These studies intended the classification of foods in the appropriate food category specified in Reg.…”