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

Abstract

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.

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

“…In a recent study carried out in Sardinia, the prevalence of E. coli VTEC was 6.6% in samples of Cerastoderma spp. and R. decussatus (Marceddu et al , 2017 ). The ten E. coli VTEC strains belonged to the serogroups O157, O26, O103, O145 and O11 and showed a complete pathogenicity profile (stx1 +, stx2 +, eae +, hlyA +) .…”

“…Bivalve molluscs transmitted illness can be either due to indigenous bacteria as Vibrio species (Smaldone et al , 2014 ; Leoni et al , 2016 ) or from non-indigenous bacteria, usually enteric bacteria, derived from fecal contamination (mostly Salmonella spp., E. coli VTEC , Shigella spp.) (Marceddu et al , 2017 ). In marine environments, Salmonella has been detected in coastal waters, molluscs, as well as other seafood products (Bazzoni et al , 2019 ; Catalao Dionisio et al , 2000 ).…”

“…Several authors reported a prevalence of Salmonella spp. in shellfish samples collected in Italy, ranging from 0 to 3.1% (Bazzoni et al , 2019 ; Carraro et al , 2015 ; Marceddu et al , 2017 ; Prato et al , 2013 ; Rubini et al , 2018 ; Sferlazzo et al ., 2018 ;). Although Salmonella spp.…”

“…Among EHEC, verotoxigenic E. coli (VTEC) are strains that produce Shiga-like toxin (verotoxin). VTEC are not commonly found in seafood, but it is well known that bivalve molluscs harvested in areas contaminated by landfill can carry verotoxigenic E. coli (Marceddu et al ., 2017 ). Moreover, VTEC have been isolated in breeding environments from different sites such as soil, manure, sewage, drinking water, irrigation water, crops, and various equipment (Avery et al , 2008 ).…”

“…The gastrointestinal tract of ruminants is the main reservoir of VTEC (Caprioli et al , 2005 ): from agricultural environments, they can be transferred to watercourses, especially during periods of high rainfall, and subsequently spread to coastal areas (Williams et al , 2008 ). Shellfish harvested in these areas can consequently concentrate the pathogen and thereby pose a risk to the health of consumers (Marceddu et al ., 2017 ). Sardinia is one of the nationally relevant Italian shellfish production areas: the annual production accounts for 83% of the regional aquaculture, and it almost exclusively rests on M. galloprovincialis (Meloni et al , 2015 ; Sferlazzo et al , 2018 ).…”