Comparison between HPLC and a commercial immunoassay kit for detection of okadaic acid and esters in Portuguese bivalves

Abstract

Liquid chromatography (HPLC), used to identify diarrhoeic shellfish poisoning (DSP) toxins in Portuguese shellfish, has detected okadaic acid (OA), dinophysistoxin-2 (DTX2) and esters of both of these. In Donax clams, a surprisingly high level of esters has been recently associated with some outbreaks of diarrhoea in shellfish consumers. In view of these events, we have proposed that screening for esters must be included in monitoring programmes for DSP toxins. HPLC is laborious, time-consuming and suffers from some interferences at low detection levels in total meat extracts. An enzyme-linked immunosorbent assay (ELISA) based on the procedure of Usagawa et al. (`DSP-Check' kit) was tested against HPLC. The `DSP-Check' kit was capable of quantitatively detecting DSP toxins in all the tested contaminated samples containing only okadaic acid, provided that the parent toxins were within the range of detection and were not in the ester form. A high correlation was observed between the two methods when appropriate dilutions were performed. The immunoassay kit tested appeared to be more sensitive, specific and faster than HPLC for determination of DSP in total shellfish meat extracts. No problems were found when using hydrolysed semi-purified extracts in order to detect esters of okadaic acid. In view of the results obtained so far, Donax clams appeared to be an excellent indicator of shellfish contamination with diarrhoeic toxins. On sandy beaches of the Portuguese southern coast, were rock mussels are not so abundant, they should be screened more often than other species in order to prevent diarrhoea in humans.