Clara Sanna

Hygiene and health risks associated with the consumption of edible lamellibranch molluscs

Edible lamellibranch molluscs are frequently the cause of very serious outbreaks of food poisoning. Microbiological suitability for human consumption, according to EC Reg. n. 1441/2007, is only based on two faecal bacteriological contamination parameters (Escherichia coli and Salmonella) and does not consider other microorganisms which are naturally present within the marine environment and are potentially pathogenic such as those belonging to the genus Vibrio. In this study, a total of 540 samples of edible lamellibranch molluscs (mussels, clams and oysters) bred in Sardinia were analyzed for E. coli and Salmonella, according to EC Reg n. 1441/2005, and for the presence of Vibrios of major public health interest. Environmental parameters (seawater temperature and salinity) were also recorded. The 40% (n=216) of samples were positive for Vibrio while the levels of E. coli were above the legal European limit only in 6.4% of samples. A correlation between the presence of micro-organisms of faecal origin and potentially harmful Vibrios to human health was not observed. Vibrio alginolyticus was the most common in 68% of isolated species, followed by Vibrio parahaemolyticus in 22.6%, Vibrio cholerae in 6% and Vibrio vulnificus in 1.1%. Virulence gene (trh sequence) was present in 1.6% of the V. parahaemolyticus-positive samples. The V. cholerae, V. vulnificus and V. alginolyticus strains detected were non toxigenic. The absence of genes encoding major virulence factors in the studied strains does not exclude the possibility of exposure to pathogenic strains. This study indicates the potential health risk associated with the presence of pathogenic Vibrios in edible lamellibranch molluscs bred in Sardinia, where shellfish production is very important to the local economy.

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

Ricotta Salata is a traditional ripened and salted whey cheese made in Sardinia (Italy) from sheeps 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.