DIRECT COMPETITIVE ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR SAXITOXIN AND NEOSAXITOXIN

Using specific ployclonal antibodies against saxitoxin (STX) or neosax itoxin (neo-STX) in combination with either STX-horseradish peroxidase (HRP) or neo-STX-HRP, the efficacy of four different direct competiti ve enzyme-linked immunoassorbent assay (dc-ELISA) formats for the anal ysis of STX and neo-STX was evaluated. Concentrations causing 50% inhi bition (ID50) Of binding of toxin-HRP conjugate to the antibodies by f ree toxins in various ELISAs were found in the range of 0.1-9.0 ng/mL. A dc-ELISA, using either anti-STX/STX-HRP or anti-neo-STX/neo-STX-HRP pairs (ID50 values of 0.28 and 0.18 ng/mL for STX and neo-STX, respec tively), was found to be most effective for the analysis of STX and ne o-STX in-naturally contaminated shellfish samples. The analytical reco veries of STX added to viscera extracts of butter clams, dungeness cra b, tanner crab, and blue mussels in the range of 0.5-10 ng/mL(-1) g(-1 ) were found to be 88.1, 92.7, 92.2, and 93.5% with coefficients of va riation of 3.9, 2.7, 9.7, and 2.8%, respectively. The detection limit for STX and neo-STX in these shellfish was around 0.2 ng/g of tissue. Gonyautoxins 1-4, but not the C group of PSP toxins, were also detecta ble in these two systems. Analysis of 154 naturally contaminated shell fish samples showed good correlation between the ELISA (STX plus neo-S TX levels) and mouse assay data. The data reported here suggest that s imultaneous analysis of both STX and neo-STX by ELISA is necessary for accurate determination of overall PSP toxin levels.