Occurrence of Salmonella enterica subsp. enterica in bivalve molluscs and associations with Escherichia coli in molluscs and faecal coliforms in seawater

Monitoring of bivalve mollusk harvesting areas: the relevance of Salmonella spp

The microbiological monitoring of bivalve mollusk harvesting areas in the Marche region is based on the parameters of Escherichia coli and Salmonella spp. However, Regulation EU/2019/627 stated criteria based on E. coli only to determine the health status of these areas. Therefore, the reason for Salmonella spp. monitoring, as provided in the Marche region, could be aimed at reducing the risk of placing on the market contaminated bivalve mollusks. This study, using the results of microbiological monitoring carried out in the Marche region from 2015 to 2022 and the methods based on Bayes' theorem and Poisson's distribution, evaluated the effectiveness and efficiency of Salmonella spp. monitoring in reducing the risk to the consumer. The results show that i) the use of a single sample unit significantly reduced the possibility of detecting non-compliance with the microbiological safety criterion; ii) the time taken to report positive results (average of approximately 10 days) did not allow the timely implementation of control measures; iii) the prevalence of positive outcomes was quite sporadic: a random trend of positivity is recognizable on a geographical and monthly basis for mussels and a geographical basis for striped clams; iv) considering the predictive value of E. coli against Salmonella spp., the specificity is very high and the negative predictive value versus Salmonella spp. would be >80%. In conclusion, the study shows that the monitoring of Salmonella spp. has a limited effect on reducing the risk to the consumer; however, in the cost/benefit assessment, other aspects not covered by this study should be considered.

Characterization of MLST-99 Salmonella Typhimurium and the monophasic variant I:4,[5],12:i:- isolated from Canadian Atlantic coast shellfish

Salmonella enterica subsp. enterica Typhimurium and its monophasic variant I 1;4,[5],12:i:- (MVST) are responsible for thousands of reported cases of salmonellosis each year in Canada, and countries worldwide. We investigated S. Typhimurium and MVST isolates recovered from raw shellfish harvested in Atlantic Canada by the Canadian Food Inspection Agency (CFIA) over the past decade, to assess the potential impact of these isolates on human illness and to explore possible routes of shellfish contamination. Whole-genome sequence analysis was performed on 210 isolates of S. Typhimurium and MVST recovered from various food sources, including shellfish. The objective was to identify genetic markers linked to ST-99, a sequence type specifically associated with shellfish, which could explain their high prevalence in shellfish. We also investigated the genetic similarity amongst CFIA ST-99 isolates recovered in different years and geographical locations. Finally, the study aimed to enhance the molecular serotyping of ST-99 isolates, as they are serologically classified as MVST but are frequently misidentified as S. Typhimurium through sequence analysis. To ensure recovery of ST-99 from shellfish was not due to favourable growth kinetics, we measured the growth rates of these isolates relative to other Salmonella and determined that ST-99 did not have a faster growth rate and/or shorter lag phase than other Salmonella evaluated. The CFIA ST-99 isolates from shellfish were highly clonal, with up to 81 high-quality single nucleotide variants amongst isolates. ST-99 isolates both within the CFIA collection and those isolated globally carried numerous unique deletions, insertions and mutations in genes, including some considered important for virulence, such as gene deletions in the type VI secretion system. Interestingly, several of these genetic characteristics appear to be unique to North America. Most notably was a large genomic region showing a high prevalence in genomes from Canadian isolates compared to those from the USA. Although the functions of the majority of the proteins encoded within this region remain unknown, the genes umuC and umuD, known to be protective against UV light damage, were present. While this study did not specifically examine the effects of mutations and insertions, results indicate that these isolates may be adapted to survive in specific environments, such as ocean water, where wild birds and/or animals serve as the natural hosts. Our hypothesis is reinforced by a global phylogenetic analysis, which indicates that isolates obtained from North American shellfish and wild birds are infrequently connected to isolates from human sources. These findings suggest a distinct ecological niche for ST-99, potentially indicating their specialization and adaptation to non-human hosts and environments, such as oceanic habitats.

Comprehensive analysis and assessment of exposure to enteric viruses and bacteria in shellfish

Shellfish species, including oysters, clams, and mussels, are extensively cultured in coastal waters. Its location is determined by factors such as nutrient availability, water temperature, tidal cycle, and the presence of contaminants such as Escherichia coli and enteric viruses. With the expansion and intensification of human activities at vicinities, the presence of anthropogenic contaminants has increased, threatening shellfish farms and consumer safety give the prevalent consumption of raw shellfish. This literature review aims to provide a comprehensive analysis of the dietary exposure and assess the risk associated with enteric viruses and bacteria detected in shellfish. The predominant bacteria and viruses detected in shellfish are reported, and the potential interrelation is discussed. The main characteristics of each contaminant and shellfish were reviewed for a more comprehensive understanding. To facilitate a direct estimation of exposure, the estimated daily intake (EDI) of bacteria was calculated based on the average levels of E. coli in shellfish, as reported in the literature. The mean daily ingestion of seafood in each of the five continents was considered. Asia exhibited the highest intake of contaminants, with an average of ±5.6 E. coli units/day.kg body weight in cockles. Simulations were conducted using recommended shellfish consumption levels established by state agencies, revealing significantly lower (p < 0.01) EDI for all continents compared to estimations based on recommended levels. This indicates a higher risk associated with healthy shellfish ingestion, potentially leading to increased intoxication incidents with a change in dietary habits. To promote a healthier lifestyle through increased shellfish consumptions, it is imperative to reduce the exposure of shellfish species to bacteria and enteric viruses. The conventional use of E. coli as the sole indicator for consumption safety and water quality in shellfish farms has been deemed insufficient. Instances where shellfish met E. coli limits established by state agencies were often found to be contaminated with human enteric viruses. Therefore, a holistic approach considering the entire production chain is necessary to support the shellfish industry and ensure food safety.

Salmonella spp. in Aquaculture: An Exploratory Analysis (Integrative Review) of Microbiological Diagnoses between 2000 and 2020

The present study aimed to characterize, through descriptive statistics, data from scientific articles selected in a systematic integrative review that performed a microbiological diagnosis of Salmonella spp. in aquaculture. Data were obtained from research articles published in the BVS, Scielo, Science Direct, Scopus and Web of Science databases. The selected studies were published between 2000 and 2020 on samples of aquaculture animal production (fish, shrimp, bivalve mollusks, and other crustaceans) and environmental samples of aquaculture activity (farming water, soil, and sediments). After applying the exclusion criteria, 80 articles were selected. Data such as country of origin, categories of fish investigated, methods of microbiological diagnosis of Salmonella spp., sample units analyzed and most reported serovars were mined. A textual analysis of the word cloud and by similarity and descending hierarchical classification with the application of Reinert's algorithm was performed using R® and Iramuteq® software. The results showed that a higher percentage of the selected articles came from Asian countries (38.75%). Fish was the most sampled category, and the units of analysis of the culture water, muscle and intestine were more positive. The culture isolation method is the most widespread, supported by more accurate techniques such as PCR. The most prevalent Salmonella serovars reported were S. Typhimurium, S. Weltevreden and S. Newport. The textual analysis showed a strong association of the terms "Salmonella", "fish" and "water", and the highest hierarchical class grouped 25.4% of the associated text segments, such as "aquaculture", "food" and "public health". The information produced characterizes the occurrence of Salmonella spp. in the aquaculture sector, providing an overview of recent years. Future research focusing on strategies for the control and prevention of Salmonella spp. in fish production are necessary and should be encouraged.

Machine learning to predict dynamic changes of pathogenic Vibrio spp. abundance on microplastics in marine environment

Microplastics are widely found in the marine environment. Recent studies have shown that pathogenic microorganisms can hitchhike on microplastics, which might act as a vector for the spread of pathogens. Vibrio spp. are known to be pathogenic to humans and can cause serious foodborne diseases. In this study, using datasets from an estuary and a mariculture zone in China, five machine learning models were established to predict the relative abundance of Vibrio spp. on microplastics. The results showed that deep neural network (DNN) model and RandomForest algorithm achieved the best predictive performance. Different data sources, data sampling, and processing methods had a little impact on the prediction performance of DNN and RandomForest models. SHapley Additive exPlanations (SHAP) indicated that salinity and temperature are the primary factors affecting the relative abundance of Vibrio spp. The prediction performances of the five machine learning models were further improved by feature selection, providing information to support future experimental research. The results of this study could help establish a long-term and dynamic monitoring system for the relative abundance of Vibrio spp. on microplastics in response to environmental factors as well as provide useful information for assessing the potential health impacts of microplastics on marine ecology and humans.

Comparison of drone and vessel-based collection of microbiological water samples in marine environments

Many water quality metrics cannot be measured in situ and require collection of a physical sample for laboratory analysis. This includes microbiological samples for detection of fecal coliform bacteria in marine and freshwater systems which are a critical component of food safety programs for human consumption of bivalve shellfish worldwide. Water sample collection programs are typically vessel-based which can be time and resource intensive. In Canada, the Canadian Shellfish Sanitation Program aims to avoid consumption of contaminated molluscan bivalves by monitoring fecal coliform bacteria through vessel-based water sample collection. Uncrewed aerial vehicles or drones are becoming more commonly used for water sample collection given their relatively low cost but are rarely used to support microbiological analyses. A prerequisite for the acceptance of a new collection method for a regulatory program is to determine if the method of sample collection affects results. To assess this potential, we designed, developed, and tested a sampling device attached to the underside of a drone to collect water samples for bacteriological analysis. Drone and vessel-based samples were collected in the same location, at the same 20-cm depth, within a minute apart, at ten different geographic locations in coastal Nova Scotia waters to compare fecal coliform counts. Bacterial count estimates obtained from drone-collected samples were not significantly different than estimates obtained from vessel-collected samples (p < 0.5). Results from this study suggest novel water sampling techniques using drones could supplement or replace traditional vessel-based sampling methods.

Prevalence, distribution and environmental effects on faecal indicator bacteria and pathogens of concern in commercial shellfish production areas in a subtropical region of a developing country (Santa Catarina, Brazil)

This paper reviews recent literature on the abundance and distribution of faecal indicator bacteria and pathogens in shellfish production areas in the state of Santa Catarina, on the subtropical coast of Brazil. This state supplies > 95% of the national production of shellfish. Microbiological monitoring data were mapped using GIS and the results compared with those from other countries. Coastal human population is the main predictive parameter for faecal bacteria in the production areas. Temporal variations of the bacteria can also be predicted by solar radiation and rainfall. The prevalence of pathogens such as hepatitis A virus, human norovirus, Salmonella spp. and Vibrio spp. does not differ substantially from that in developed countries. The information reported here can be used to inform development of microbiological risk profiles for shellfish production areas.

Prevalence of invA Gene of Salmonella spp. in Fish and Fishery Resources from Manila Bay Aquaculture Farms Using Real-Time PCR

Manila Bay contributes significantly to the Philippines’ economy through industry, trade, tourism, and agriculture. However, microbiological contamination in the bay is putting it at risk in the present. Pathogen contamination of the water poses a serious threat to food safety, implicating public health. To address these concerns, the present study examined the prevalence of Salmonella in six different aquaculture commodities, Perna viridis (mussel), Crassostrea iridalei (oyster), Scylla serrata (crab), Penaeus spp. (shrimp), Oreochromis niloticus (tilapia), and Chanos chanos (milkfish), as well as in environmental water from growing areas. A tandem approach of culture-based and real-time PCR methods for the isolation and identification of Salmonella was carried out. To accurately identify the isolates, a real-time PCR Taqman assay based on the invA gene was used. Among the fishery resources examined, no positive samples were observed from C. chanos and O. niloticus. In addition, Salmonella was found in twenty (20) samples, representing 16.26% of all aquaculture commodities collected. Furthermore, Salmonella was found in 13.58% of the 81 environmental water samples examined. P. viridis had the highest prevalence of 55.55% out of 18 samples examined. Samples contaminated with Salmonella failed to meet the regulatory limits set by BFAR FAO 210 series 2001 and EC No. 2073/2005. In addition, it was observed that the sample matrix had a significant impact on the presence of Salmonella (p < 0.05). However, the spatial and temporal distribution of Salmonella did not vary greatly (p > 0.05). This study underscores the importance of imposing strict policies by regulatory bodies to prevent diseases, thus avoiding severe health implications.

New Trends in the Occurrence of Yessotoxins in the Northwestern Adriatic Sea

Yessotoxins (YTXs) are polycyclic toxic ether compounds produced by phytoplanktonic dinoflagellates which accumulate in filter-feeding organisms. We know that the water temperature in our areas Northwestern Adriatic Sea is optimal for the growth of potentially toxic algae (around 20 °C). In recent years, these temperatures have remained at these levels for longer and longer periods, probably due to global warming, which has led to an excessive increase in toxin levels. The interruption of mussel harvesting caused by algae negatively affects farmers’ revenues and the availability of local fish, causing a major economic loss in Italy’s main shellfish sector. Methods: In the nine years considered, 3359 samples were examined: 1715 marine waters, 73 common clams; 732 mussels; 66 oysters; and 773 veracious clams. Bivalve molluscs were examined for the presence of marine biotoxins, including YTXs, while potentially toxic algae, including those producing YTXs, were searched for and counted in marine waters. The method adopted for the quantification of lipophilic toxins involves the use of an LC-MS/MS system. The enumeration of phytoplankton cells was performed according to the Utermhöl method. Results: Between 2012 and 2020, 706 molluscs were tested for YTXs. In total, 246 samples tested positive, i.e., 34.84%. Of the positive samples, 30 exceeded the legal limit. Conclusion: In this regard, it is essential to develop and activate, as soon as possible, an “early warning” system that allows a better control of the production areas of live bivalve molluscs, thus allowing an optimal management of the plants in these critical situations.

Prevalence, typing and antimicrobial resistance of Salmonella isolates from commercial shellfish in the North coast of Morocco

Salmonellosis is one of the most common foodborne illnesses in the world. The irrational use of antibiotics in medicine and in animal nutrition has greatly favored the emergence and spread of resistant strains of non-typhoid Salmonella. This study aims the determination of the prevalence of Salmonella in bivalve mollusks in Northern Morocco, as well as the molecular typing and antibiotic susceptibility testing of the strains isolated from positive samples. In total, 150 samples from shellfish composed of mussels (Mytilus galloprovincialis), clams (Callista chione and Ruditapes descussatus) and oysters (Magallana gigas). Isolated Salmonella were characterized by Molecular techniques PCR, MLST and MLVA, phylogenetically grouped by MLSA, and susceptibilities were determined for 30 antimicrobial drugs using microdilution method by the BD Phoenix Automated Microbiology System. Prevalence of Salmonella enterica subsp. enterica was 12.67%, grouped in four serovars identified as Chester, Hadar, Typhimurium and Kentucky. Five different MLST STs (sequence types) were detected, ST1954 being the most common, which was mostly found in Chester isolates. Forty-two percent of the isolates showed resistance to more than one antibiotic, especially trimethoprim, sulfa drugs, quinolones and β-lactam. There was a marked change in the serovars and antimicrobial resistance profiles of the Salmonella isolates in this study compared to those in previous studies.

Preliminary Microbiological Coastal Water Quality Determination along the Department of Atlántico (Colombia): Relationships with Beach Characteristics

Beach water quality is an important factor concerning public health and tourism linked to the “Sun, Sea and Sand” market and is usually assessed in international regulations by the quantification of Escherichia coli and enterococci counts. Despite Salmonella spp. detection not being included in international normative, the presence/absence of this bacteria is also an indicator of seawater quality. The objective of this study was to determine microbiological quality of beach water at 14 beaches along the Department of Atlántico (Colombia) and its relationship with beach characteristics as beach typology (i.e., urban, village, rural and remote areas), presence of beach facilities (e.g., bars, restaurants, etc.) and streams outflowing into the coastline. Sampling program aimed to analyse E. coli and Salmonella spp., by culture-based and real time PCR methods, respectively. Microbiological outcomes were compared with beach characteristics, and a cluster analysis was performed. E. coli and Salmonella spp. were detected in 70% and 20% of samples, respectively. Highest E. coli counts were observed at beaches classified as urban and at Sabanilla, a rural beach with presence of numerous beach restaurants/bars. Salmonella spp. presence was associated with streams that lack wastewater treatment systems. Cluster analysis clearly evidenced the relationship between E. coli and Salmonella spp. and beach characteristics, allowing to obtain indications to implement management programs. According to data obtained, monitoring programs have to be especially carried out in urban areas and at places with beach facilities. This could enhance microbiological water quality and consequently, beachgoers safety and touristic beach attractiveness to international visitors.

Enumeration of Escherichia coli and determination of Salmonella spp. and verotoxigenic Escherichia coli in shellfish (Mytilus galloprovincialis and Ruditapes decussatus) harvested in Sardinia, Italy

The aim of the present study was to evaluate the occurrence of Salmonella spp., Verotoxigenic E. Coli (VTEC) and enumerate E. coli in shellfish (Mytilus galloprovincialis and Ruditapes decussatus) collected before and after depuration from two class B harvesting areas located in Sardinia (Italy). All the samples were analyzed for Salmonella spp. detection according to European Commission Regulation (EC) 2073/2005 and examined using the five tube Most-Probable-Number (MPN) method for enumeration of E. coli in accordance with the European Union reference method ISO 16649-3:2015. E. coli VTEC was investigated following a direct multiplex Polymerase Chain Reaction (PCR) screening test. The enumeration of E. coli met the European law limit for Class A areas of 230 MPN/100g. The averaged enumeration of E. coli in samples of M. galloprovincialis and R. decussatus collected at the harvesting time was 39 and 37 MPN/100 g respectively. The average contamination levels in samples collected after purification were 58 MPN/100g (M. galloprovincialis) and 32 MPN/100 g (R. decussatus). E. coli VTEC was not detected, on the contrary, Salmonella ser. Typhimurium was detected in one sample of M. galloprovincialis and in one sample of R. decussatus collected at the harvesting time. No significant associations were observed between E. coli levels in shellfish and environmental parameters of water or with the detection of Salmonella ser. Typhimurium in M. galloprovincialis and R. decussatus samples. Nevertheless, the occurrence of Salmonella ser. Typhimurium, involved in human infection outbreaks, should be considered a potential risk for consumers.

Bacterial metagenome analysis of Mytilus galloprovincialis collected from Istanbul and Izmir coastal stations of Turkey

Mytilus galloprovincialis is a marine mollusk belonging to the Bivalvia class. It has been distributed largely in Turkish shores and worldwide aquatic environments. Besides being known as an environmental pollution indicator, it is highly consumed as a food and has a high economic value. Due to their nutritional mechanisms by filtering water, they are affected by pollution in seawater and mussels can host-microbial diversity of environmental origin as well as pathogenic bacteria. Therefore, in this study, bacterial species found in Mediterranean mussels collected from the coastal stations of Istanbul [Rumeli Kavagi (RK), Kucukcekmece (KC)], and Izmir [(Foca (MF), Urla (MU)] were investigated and compared with microbiological and metagenomic analyses. According to microbiological analysis results, 34 mussel-associated Enterobacteriaceae and Vibrionaceae family members were identified. As a result of the culture-independent metagenomic analysis, taxonomic groups for each station were identified and compared based on Operational Taxonomic Unit data. For all stations, the most abundant bacterial genera were the unclassified bacterial genera. The total number of mussel-related total richness identified in all groups was 4889 (RK = 1605; KC = 1930; MF = 1508; and MU = 1125). According to the metagenomic data obtained in this study, different relative amounts of Lachnospiraceae and Bacteroidetes taxa groups were reported for all stations. The pathogenic bacterial genera identified by metagenomic analyses which may be significant for the public health are Arcobacter, Clostridium, Aeromonas, Vibrio, Escherichia_Shigella, Klebsiella, Campylobacter, Helicobacter, Pseudomonas, Morganella, Serratia, Corynebacterium, Enterococcus, Staphylococcus, Yersinia, Mycoplasma, Brucellaceae_unclassified, Pantoea, and Proteus.

Bacterial and Viral Investigations Combined with Determination of Phytoplankton and Algal Biotoxins in Mussels and Water from a Mediterranean Coastal Lagoon (Sardinia, Italy)

Calich Lagoon is a Mediterranean coastal lagoon located along the northwestern coast of Sardinia (Italy). The connection to marine and fresh water determines the high productivity of this coastal lagoon. Despite its great potential and the presence of natural beds of bivalve mollusks (Mytilus galloprovincialis), the lagoon has not yet been classified for shellfish production. In this study, through a multidisciplinary approach, the presence of several bacterial pathogens (Escherichia coli, Salmonella spp., and Vibrio spp.) and viral pathogens (hepatitis A virus and norovirus genogroups I and II) was evaluated from March 2017 to February 2018. In addition, phytoplankton composition in lagoon waters and associated algal biotoxins (paralytic and diarrhetic shellfish poisoning) in mussels were also monitored. The aim of this study was to provide useful data to improve knowledge about their seasonal presence and to assess the potential risk for public health, as well as to provide input for future conservation and management strategies. In mussels, Salmonella spp. were found in spring, along with E. coli, but Salmonella spp. were not found in autumn or winter, even though E. coli was detected in these seasons. Vibrio parahaemolyticus was found in autumn and winter, but not in spring. Norovirus genogroups I and II were found in winter samples. None of the bacteria were found in summer. Algal biotoxins have never been detected in mussel samples. Among potentially harmful phytoplankton, only Pseudo-nitzschia spp. were present, mainly in summer. The results showed that a possible bacterial and viral contamination, together with the presence of potentially toxic microalgae, is a real problem. Therefore, the development of natural resource management strategies is necessary to ensure the good quality of waters and guarantee the protection of consumers.

Occurrence and Phenotypic and Molecular Characterization of Antimicrobial Resistance of Salmonella Isolates from Food in Tunisia

HIGHLIGHTS

Multidrug-resistant Salmonella isolates have been recovered from food in Tunisia. Salmonella isolates from food are resistant to fluoroquinolones and cephalosporins. Surveillance of the antimicrobial susceptibility of foodborne bacteria is needed in Tunisia.

Characterization of quorum sensing genes and N-acyl homoserine lactones in Citrobacter amalonaticus strain YG6

In the phylum of Proteobacteria, quorum sensing (QS) system is widely driven by synthesis and response of N-acyl homoserine lactone (AHL) signalling molecules. AHL is synthesized by LuxI homologue and sensed by LuxR homologue. Once the AHL concentration achieves a threshold level, it triggers the regulation of target genes. In this study, QS activity of Citrobacter amalonaticus strain YG6 which was isolated from clams was investigated. In order to characterise luxI/R homologues, the genome of C. amalonaticus strain YG6 (4.95 Mbp in size) was sequenced using Illumina MiSeq sequencer. Through in silico analysis, a pair of canonical luxI/R homologues and an orphan luxR homologue were identified and designated as camI, camR, and camR2, respectively. A putative lux box was identified at the upstream of camI. The camI gene was cloned and overexpressed in E. coli BL21 (DE3)pLysS. High-resolution triple quadrupole liquid chromatography mass spectrometry (LC-MS/MS) analysis verified that the CamI is a functional AHL synthase which produced multiple AHL species, namely N‑butyryl‑l‑homoserine lactone (C4-HSL), N‑hexanoyl‑l‑homoserine lactone (C6-HSL), N‑octanoyl‑l‑homoserine lactone (C8-HSL), N‑tetradecanoyl‑l‑homoserine lactone (C14-HSL) and N‑hexadecanoyl‑l‑homoserine lactone (C16-HSL) in C. amalonaticus strain YG6 and camI gene in recombinant E. coli BL21(DE3)pLysS. To our best knowledge, this is the first functional study report of camI as well as the first report describing the production of C14-HSL by C. amalonaticus.

Determination of Salmonella spp., E. coli VTEC, Vibrio spp., and Norovirus GI-GII in Bivalve Molluscs Collected from Growing Natural Beds in Sardinia (Italy)

The aim of the present study was to evaluate the presence of Salmonella spp., verotoxigenic E. coli (VTEC), Vibrio spp., and Norovirus GI-GII in bivalve molluscs, cockles, and European grooved carpet shells (Cerastoderma spp. and Ruditapes decussatus) collected from a class B growing natural bed in Sardinia (Italy). All of the samples were analysed for Salmonella spp. detection according to European Commission Regulation (EC) 2285/2015. Detection and enumeration of Vibrio spp. were performed according to previously published methods. Presumptive identification of Vibrio spp. isolates was performed by means of conventional biochemical tests. E. coli VTEC was isolated following a direct multiplex polymerase chain reaction (PCR) screening test. Norovirus GI and GII were determined by reverse transcriptase-polymerase chain reaction (RT-PCR). No Salmonella spp. were detected. The prevalence of Vibrio spp. was 90%, and the average contamination levels were 3.19 ± 1.07 and 2.84 ± 0.31 Log10 cfu/g in cockles and European grooved carpet shells, respectively. The prevalence of E. coli VTEC was 6.6%. All of the isolates showed a complete pathogenicity profile. The presence of Norovirus was highlighted in 25% of European grooved carpet shells samples. Results showed the typical microbiological profile of bivalve molluscs collected from backwaters and confirmed the capability of shellfish to accumulate E. coli VTEC, pathogenic vibrios, and Norovirus. The presence of such pathogens in shellfish is of major concern for the safety of consumers.