A dot enzyme-linked immunosorbent assay for detection of antibodies against Entamoeba histolytica

A visual micro-dot enzyme-linked immunosorbent assay (ELISA) based on detection of antibodies against soluble antigens of axenically grown cultures of Entamoeba histolytica is described. The antigen was spotted on a nitrocellulose sheet, the unsaturated sites blocked with bovine serum albumin (BSA) and incubated with 3-fold dilutions of patient sera followed by incubation with protein A conjugated to peroxidase. Enzymic activity was evidenced using the substrate 4-chloro-1-naphthol. A positive reaction produced a blue spot. The sensitivity of the assay was better and comparable to the indirect haemagglutination assay (IHA) and plate ELISA. The entire assay could be completed within 3 h. Antigen-loaded and pre-blocked nitrocellulose strips could be stored up to 3 months at room temperature and 37 degrees C.