The aim of the present study was to evaluate Vibrio parahaemolyticus occurrences in bivalve molluscs harvested from Sardinian coastal environments between 2013 and 2015. The prevalence of pathogenic V. parahaemolyticus isolates is based on the detection of the two major virulence genes thermostable direct hemolysin (tdh) and thermolabile hemolysin (trh) To assess changes between 2011 and 2018 in the prevalence of V. parahaemolyticus in bivalve molluscs, we compared our results with those of previous investigations. In total, 2,933 samples were collected: 1,079 in 2013, 1,288 in 2014, and 566 in 2015. The mean prevalence of V. parahaemolyticus in shellfish was 3.5% in 2013, 1.7% in 2014, and 3.5% in 2015. The highest percentage of positive samples in 2013 and 2014 was observed in clams (3.5% and 2.7%, respectively), whereas in 2015, it was reported in oysters (15.1%). By comparing the sampling period of 2011-2014 with that of 2015-2018, an increase in the prevalence of V. parahaemolyticus was observed in shellfish (p < 0.05). In parallel, 208 potentially enteropathogenic V. parahaemolyticus strains were identified through the years 2011-2018 and, in particular, 10 trh+ and six tdh+ isolates. Our present study provides information regarding trends of V. parahaemolyticus occurrences in bivalve molluscs harvested from Sardinian coastal environments between 2011 and 2018 suggesting that the prevalence varies depending on the sampling period and shellfish species.

In the present study, we investigated the presence, seasonal distribution, and biomolecular characteristics of Vibrio parahaemolyticus and Vibrio vulnificus in samples of bivalve mollusks (Mytilus galloprovincialis, Crassostrea gigas, and Ruditapes decussatus) harvested and marketed in Sardinia (Italy) between 2017 and 2018. A total of 435 samples were submitted for qualitative determination of Vibrio spp., V. parahaemolyticus, and V. vulnificus. Potentially enteropathogenic isolates were detected with biomolecular methods. The overall prevalence of Vibrio spp. was 7.6%. The highest Vibrio prevalence was found in R. decussatus (8.3%). The prevalences of V. parahaemolyticus and V. vulnificus were 2.7 and 4.8%, respectively. Higher prevalences of V. parahaemolyticus and V. vulnificus were found in R. decussatus (4.2%) and C. gigas (6.2%), respectively. Only two pathogenic V. parahaemolyticus strains were recovered (genotypes: tdh- and trh-F; tdh-F and trh-), both from M. galloprovincialis. None of the isolates were tdh-F and trh-F. Pathogenic Vibrio infections are often underestimated, and human infections are increasing in Europe. European data on the true distribution of Vibrionaceae are scarce, and the results of the present study highlight the need of constant monitoring to update the distribution of pathogenic vibrios.

This work reports the first communication relating to the presence of yessotoxins in Mytilus galloprovincialis from coastal mussel farms (Sardinia, western Mediterranean) detected during 2008 and 2013 through a monitoring programme. The paper emphasizes how the changes both in yessotoxin permitted limits and used methods, established by legislation, have influenced the interpretation of the obtained results. Consequently, the samples that resulted negative during 2008 would have been positive until August 2013 and negative from September 2013 up to now, and the samples that were positive in 2013 would have been positive in 2008 and negative nowadays, according to Regulation currently in force. Regular monitoring of biotoxins demonstrated that, although yessotoxins have been rarely present in the past in Sardinia, they may cause toxicity in shellfish. So, it’s important to keep up on legislation’s changing and laboratory methods.

Sardinia (Italy, north-western Mediterranean) is a commercially important producer of edible bivalve molluscs. Since the early 2000s, it was subjected to recurring cases of mussel farm closures due to toxic algal poison. Here, we present the studies on toxin concentrations and the associated potentially toxic phytoplankton distribution and abundances carried out by a regular monitoring programme in Sardinian shellfish areas, from January to May 2015. Diarrheic shellfish poisoning (DSP) toxins were detected in several bivalve molluscs samples, while paralytic shellfish poisoning (PSP) and paralytic shellfish poisoning toxins were present just once, without exceeding the legal limits. Potentially toxic algal species have been constantly present. Pseudo-nitzschia species were present during the entire study often with high abundances, while Dinophysis species reached high densities sporadically. Among PSP phytoplankton, only Alexandrium minutum Halim was found. The data obtained in this study showed an increase in the DSP toxicity in mussels in Sardinia. No clear relation between the occurrence of toxins in shellfish and the presence of potentially toxic algal species was found, although a slight correlation between DSP toxins and Dinophysis species could be supported.