Quantification methods for Alexandrium catenella, a toxic dinoflagellate: Comparison of competitive enzyme-linked immunosorbent assay and sandwich hybridization integrated with a nuclease protection assay

Alexandrium catenella (Whedon et Kofoid) Balech, a toxic dinoflagellate, is a bloom-forming planktonic species in cold water coastal regions. It produces strong paralytic shellfish poisoning (PSP) toxins which are transmitted via tainted shellfish. These toxins can affect humans, other mammals, fish and birds. In this study, polyclonal antiserum against A. catenella was produced, and a competitive enzyme-linked immunosorbent assay (cELISA) was developed to detect A. catenella. The antiserum against A. catenella showed good specificity, the linear detection range was relatively large, between 38 and 600,000 cells. In addition, specific probes were designed to target the small subunit ribosomal RNA (SSU rRNA) of A. catenella, and quantitative sandwich hybridization integrated with a nuclease protection assay (NPA-SH) was established in order to identify and quantify A. catenella. The NPA-SH assay did not show good specificity as well as cELISA, by which A. catenella and A. tamarense could not be distinguished. Samples in different cell growth phases were analyzed with cELISA and NPA-SH. The results showed that the cell concentration calculated by cELISA was very similar with microscopy, while that of NPA-SH was sometimes higher than that of microscopy, especially in log phase. Comparing the two methods, both assays allow rapid identification of A. catenella without time-consuming microscopy when multiple sites need to be considered in routine monitoring. Meanwhile, cELISA was more specific and accurate in detection of A. catenella than NPA-SH.