Differentiation of Entamoeba histolytica from Entamoeba dispar by PCR-coupled nonisotopic SSCP analysis

Entamoeba histolytica is a pathogenic protozoan parasite, which causes amoebic colitis, dysentery and liver abscesses in humans. Since the cyst and small trophozoite stages of this parasite are indistinguishable by light microscopy from Entamoeba dispar (which is nonpathogenic), specific diagnosis is compromised. To overcome this limitation, a PCR-coupled SSCP approach, utilising a sequence difference of 4.6% in a short region ( approximately 173-174 bp) of the small subunit of nuclear ribosomal DNA, was evaluated for the differentiation of the two species of Entamoeba. Including a range of well-defined control DNA samples (n = 67) to evaluate the specificity of the PCR, 45 DNA samples representing E. histolytica and E. dispar from human faecal samples were tested by SSCP, and unequivocal delineation between the species was achieved. This SSCP approach should provide a practical tool for the specific diagnosis of E. histolytica in humans and for investigating its epidemiology.