Application of rapid test kits for the determination of Diarrhetic Shellfish Poisoning (DSP) toxins in bivalve molluscs from Great Britain

A Comparative Analysis of Methods (LC-MS/MS, LC-MS and Rapid Test Kits) for the Determination of Diarrhetic Shellfish Toxins in Oysters, Mussels and Pipis

Rapid methods for the detection of biotoxins in shellfish can assist the seafood industry and safeguard public health. Diarrhetic Shellfish Toxins (DSTs) are produced by species of the dinoflagellate genus Dinophysis, yet the comparative efficacy of their detection methods has not been systematically determined. Here, we examined DSTs in spiked and naturally contaminated shellfish–Sydney Rock Oysters (Saccostrea glomerata), Pacific Oysters (Magallana gigas/Crassostrea gigas), Blue Mussels (Mytilus galloprovincialis) and Pipis (Plebidonax deltoides/Donax deltoides), using LC-MS/MS and LC-MS in 4 laboratories, and 5 rapid test kits (quantitative Enzyme-Linked Immunosorbent Assay (ELISA) and Protein Phosphatase Inhibition Assay (PP2A), and qualitative Lateral Flow Assay (LFA)). We found all toxins in all species could be recovered by all laboratories using LC-MS/MS (Liquid Chromatography—tandem Mass Spectrometry) and LC-MS (Liquid Chromatography—Mass Spectrometry); however, DST recovery at low and mid-level concentrations (<0.1 mg/kg) was variable (0–150%), while recovery at high-level concentrations (>0.86 mg/kg) was higher (60–262%). While no clear differences were observed between shellfish, all kits delivered an unacceptably high level (25–100%) of falsely compliant results for spiked samples. The LFA and the PP2A kits performed satisfactorily for naturally contaminated pipis (0%, 5% falsely compliant, respectively). There were correlations between spiked DSTs and quantitative methods was highest for LC-MS (r² = 0.86) and the PP2A kit (r² = 0.72). Overall, our results do not support the use of any DST rapid test kit as a stand-alone quality assurance measure at this time.

Current Trends and Challenges for Rapid SMART Diagnostics at Point-of-Site Testing for Marine Toxins

In the past twenty years marine biotoxin analysis in routine regulatory monitoring has advanced significantly in Europe (EU) and other regions from the use of the mouse bioassay (MBA) towards the high-end analytical techniques such as high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS). Previously, acceptance of these advanced methods, in progressing away from the MBA, was hindered by a lack of commercial certified analytical standards for method development and validation. This has now been addressed whereby the availability of a wide range of analytical standards from several companies in the EU, North America and Asia has enhanced the development and validation of methods to the required regulatory standards. However, the cost of the high-end analytical equipment, lengthy procedures and the need for qualified personnel to perform analysis can still be a challenge for routine monitoring laboratories. In developing regions, aquaculture production is increasing and alternative inexpensive Sensitive, Measurable, Accurate and Real-Time (SMART) rapid point-of-site testing (POST) methods suitable for novice end users that can be validated and internationally accepted remain an objective for both regulators and the industry. The range of commercial testing kits on the market for marine toxin analysis remains limited and even more so those meeting the requirements for use in regulatory control. Individual assays include enzyme-linked immunosorbent assays (ELISA) and lateral flow membrane-based immunoassays (LFIA) for EU-regulated toxins, such as okadaic acid (OA) and dinophysistoxins (DTXs), saxitoxin (STX) and its analogues and domoic acid (DA) in the form of three separate tests offering varying costs and benefits for the industry. It can be observed from the literature that not only are developments and improvements ongoing for these assays, but there are also novel assays being developed using upcoming state-of-the-art biosensor technology. This review focuses on both currently available methods and recent advances in innovative methods for marine biotoxin testing and the end-user practicalities that need to be observed. Furthermore, it highlights trends that are influencing assay developments such as multiplexing capabilities and rapid POST, indicating potential detection methods that will shape the future market.

Dinophysis acuta in Scottish Coastal Waters and Its Influence on Diarrhetic Shellfish Toxin Profiles

Diarrhetic shellfish toxins produced by the dinoflagellate genus Dinophysis are a major problem for the shellfish industry worldwide. Separate species of the genus have been associated with the production of different analogues of the okadaic acid group of toxins. To evaluate the spatial and temporal variability of Dinophysis species and toxins in the important shellfish-harvesting region of the Scottish west coast, we analysed data collected from 1996 to 2017 in two contrasting locations: Loch Ewe and the Clyde Sea. Seasonal studies were also undertaken, in Loch Ewe in both 2001 and 2002, and in the Clyde in 2015. Dinophysis acuminata was present throughout the growing season during every year of the study, with blooms typically occurring between May and September at both locations. The appearance of D. acuta was interannually sporadic and, when present, was most abundant in the late summer and autumn. The Clyde field study in 2015 indicated the importance of a temperature front in the formation of a D. acuta bloom. A shift in toxin profiles of common mussels (Mytilus edulis) tested during regulatory monitoring was evident, with a proportional decrease in okadaic acid (OA) and dinophysistoxin-1 (DTX1) and an increase in dinophysistoxin-2 (DTX2) occurring when D. acuta became dominant. Routine enumeration of Dinophysis to species level could provide early warning of potential contamination of shellfish with DTX2 and thus determine the choice of the most suitable kit for effective end-product testing.

Variability and profiles of lipophilic toxins in bivalves from Great Britain during five and a half years of monitoring: Okadaic acid, dinophysis toxins and pectenotoxins

Official control biotoxin testing of bivalve molluscs from Great Britain has been conducted by Cefas for over a decade. Reflecting the changes in legislation, bioassays were gradually replaced by analytical methods, firstly for analysis of Paralytic shellfish toxins, followed by introduction of liquid chromatography tandem mass spectrometric (LCMS/MS) method for lipophilic toxins (LTs) in 2011. Twelve compounds, representing three main groups of regulated lipophilic toxins, as well as two non-regulated cyclic imines were examined in over 20,500 samples collected between July 2011 and December 2016. The toxins belonging to Okadaic acid (OA) group toxins were the most prevalent and were quantified in 23% of samples, predominantly from Scotland. The temporal pattern of OA group occurrences remained similar each year, peaking in summer months and tailing off during autumn and winter, however their abundance and magnitude varied between years significantly, with concentrations reaching up to 4993 μg OA eq./kg. Three toxin profiles were identified, reflecting the relative contribution of the two main toxins, OA and dinophysis toxin-2 (DTX2). Dinophysis toxin-1 (DTX1) was less common and was never detected in samples with high proportions of DTX2. Inter-annual changes in profiles were observed within certain regions, with the most notable being an increase of DTX2 occurrences in north-west Scotland and England in the last three years of monitoring. In addition, seasonal changes of profiles were identified when OA, the dominant toxin in early summer, was replaced by higher proportions of DTX2 in late summer and autumn. The profile distribution possibly reflected the availability of individual Dinophysis species as a food source for shellfish, however persistence of DTX2 during autumn and winter in mussels might have also been attributed to their physiology. Mussels were the only species with higher average proportions of non-esterified toxins, while Pacific oysters, cockles, surf clams, razors and queen scallops contained almost exclusively ester forms. In addition, a temporal change in proportion of OA and DTX2 free form was observed in mussels. Pectenotoxin-2 (PTX2) was quantified only on rare occasions.