We surveyed the occurrence of toxigenic cyanobacteria, the mcyA component of the microcystin synthetase gene and microcystin in aquatic systems in temperate Australia and tropical Thailand. The survey methods, microscopy, protein phosphatase inhibition assay, enzyme linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR), were evaluated for screening raw water for public health risk from microcystin producing toxigenic cyanobacteria.

Three tests, ELISA, PCR and protein phosphatase inhibition (PPi), were judged very useful because of their sensitivity and speed of analysis. ELISA ranked slightly higher because of its superior specificity for microcystin. The PCR was highly sensitive, but there were three false negative results, whilst the PPi was cheap but less specific than ELISA. Some of the microcystin quantifications results were validated by high performance liquid chromatography (HPLC).

The combination of a gene probe for the mcy gene complex with an ELISA or PPi assay for microcystin is proposed as a powerful screening technique for raw waters that can provide multi-level risk assessment including ‘incipient risk’, when microcystin producing cyanobacterial strains are rare and microcystin concentrations are below the detection limit for biochemical or chromatographic analyses.