Tetrodotoxins (TTXs) and Vibrio alginolyticus in Mussels from Central Adriatic Sea (Italy): Are They Closely Related?

Simone Bacchiocchi,Francesca Leoni,Stefano Accoroni,Debora Campacci,Maria Elisa Giuliani,Alessandra Dubbini,Melania Siracusa,Arianna Piersanti,Arianna Stramenga,Stefania Gorbi,Tamara Tavoloni

doi:10.3390/md19060304

Abstract

Tetrodotoxins (TTXs), potent neurotoxins, have become an increasing concern in Europe in recent decades, especially because of their presence in mollusks. The European Food Safety Authority published a Scientific Opinion setting a recommended threshold for TTX in mollusks of 44 µg equivalent kg−1 and calling all member states to contribute to an effort to gather data in order to produce a more exhaustive risk assessment. The objective of this work was to assess TTX levels in wild and farmed mussels (Mytilus galloprovincialis) harvested in 2018–2019 along the coastal area of the Marche region in the Central Adriatic Sea (Italy). The presence of Vibrio spp. carrying the non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) genes, which are suspected to be involved in TTX biosynthesis, was also investigated. Out of 158 mussel samples analyzed by hydrophilic interaction liquid chromatography coupled with tandem mass spectrometry (HILIC-MS/MS), 11 (7%) contained the toxins at detectable levels (8–26 µg kg−1) and 3 (2%) contained levels above the EFSA safety threshold (61–76 µg kg−1). Contaminated mussels were all harvested from natural beds in spring or summer. Of the 2019 samples, 70% of them contained V. alginolyticus strains with the NRPS and/or PKS genes. None of the strains containing NRPS and/or PKS genes showed detectable levels of TTXs. TTXs in mussels are not yet a threat in the Marche region nor in Europe, but further investigations are surely needed.

Highlights

Tetrodotoxins (TTXs) are potent neurotoxins, which have been known for centuries and have been implicated worldwide in pufferfish poisoning
This work aimed to study the presence of TTXs in mussels (Mytilus galloprovincialis) from the Marche region, Central Adriatic Sea (Italy), and the possible correlation with symbiotic vibrios over a two-year period (2018–2019)
The toxin levels were lower than the limit of detection (LOD), in 11 (7%) they were between the LOD and limit of quantification (LOQ), and only 3 (2%) of them showed levels between 61 and 76 μg kg−1

Summary

Introduction

Tetrodotoxins (TTXs) are potent neurotoxins, which have been known for centuries and have been implicated worldwide in pufferfish poisoning. TTXs are alkaloids with a guanidinium moiety connected to a highly oxygenated carbon skeleton [1,2,3,4]. The guanidinium group is responsible for their toxicity; it binds to the voltage-gated Na+. Symptoms of tetrodotoxin poisoning progress from tongue and lip numbness to progressive paralysis and, in the worst cases, death as a result of respiratory failure. Tetrodotoxin (TTX) is the best known member of the group, but it co-exists with some other natural occurring congeners. There have been 30 structural analogues reported to date, with different degrees of toxicity depending on their chemical structure [7,8]

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