Nuove metodologie per indagare i fattori che influenzano la composizione della comunità di specie di Vibrio nel microbiota di Ruditapes philippinarum e la loro applicazione sulla sicurezza alimentare nella produzione dei molluschi

As filter-feeders, bivalve molluscs accumulate several Vibrio species in their edible tissues. Among these species, Vibrio alginolyticus, Vibrio cholerae, Vibrio parahaemolyticus and Vibrio vulnificus represent a risk to human health. Given the worldwide human consumption of bivalve molluscs, an accurate and reliable characterisation of the Vibrio community associated with these seafood products represents a key issue to ensure food safety in shellfish production. The goal of this study was to provide new insights about natural Vibrio species contamination and the possible risk for human health present in a shellfish product of high commercial interest, namely the Manila clam (Ruditapes philippinarum). To achieve this goal, a new metabarcoding approach was developed based on recA–pyrH housekeeping genes to characterise the Vibrio biodiversity down to the species level, with a specific focus on detecting the main Vibrio human pathogens. First, this approach made it possible to study changes in Vibrio biodiversity in the R. philippinarum microbiota in response to depuration. In particular, Vibrio spp. and human pathogens were found in the depurated clams. Moreover, recA–pyrH metabarcoding allowed the evaluation of culture-dependent and culture-independent methods to characterise the Vibrio community composition, with a focus on Vibrio human pathogens. The application of recA–pyrH metabarcoding directly to homogenate clam samples as well as plating samples on Marine Agar medium could be a useful screening approach to detect Vibrio human pathogens in seafood products. Moreover, culture-dependent shotgun metagenomics was a valid approach for an accurate characterisation of the living fraction of the Vibrio community. The characterisation of the Vibrio community composition of all samples collected during the 3-year PhD project revealed a high frequency of detection of Vibrio pathogens in clams collected during the summer. The season factor also affected the biodiversity of marine bacteria and the Vibrio community composition of homogenate clam samples. V. cholerae, V. parahaemolyticus and V. vulnificus were found in homogenate clam samples from seven sampled shellfish farming areas operating along the North-east Adriatic coast. Taken together, the results highlight the importance to include the detection of Vibrio species in the official microbiological seafood control measures. This endeavour could be doubly useful: it would allow the acquisition of Vibrio surveillance data – which is necessary to maintain updated knowledge about the real Vibrio risk associated with seafood consumption – and it would contribute to prevent the spread of the human vibriosis.