Screening of paralytic shellfish poisoning toxins in naturally occurring samples with three different direct competitive enzyme-linked immunosorbent assays

Among three direct competitive enzyme-linked immunosorbent assays (dc-ELISA) tested, a protocol using either anti-saxitoxin (STX)/STX-horseradish peroxidase (HRP) or anti-neo-STX/STX-HRP pairs was found to be most effective for screening paralytic shellfish poisoning (PSP) toxins in contaminated shellfish. An excellent agreement between the total PSP toxins (STX plus neo-STX levels) obtained by ELISA and by mouse assay was found. Analysis of 1540 naturally contaminated samples revealed that 211 (13.6%) samples were positive by the ELISA as compared with 175 (11.3%) by the mouse assays at the threshold level of 80 mu g/100 g of sample. The distributions of the toxins at levels >40 and >80 mu g/100 g in 1540 samples obtained by different ELISA formats are presented. The total PSP toxin levels (STX plus neo-STX) obtained from simultaneous analysis of both STX and neo-STX by ELISA are valid for accurate screening for the presence of PSP toxins in these samples and could eliminate as much as 80-85% of the samples needed to run a mouse assay.