Genomic DNA differences between pathogenic and nonpathogenic Entamoeba histolytica.

cDNA libraries were constructed from pathogenic (HM-1:IMSS) and nonpathogenic (SAW 1734) isolates of Entamoeba histolytica. A cDNA clone (cEH-P1) specific for pathogenic amoebae was identified by screening with a pool of sera from patients with invasive amoebiasis that had been absorbed with nonpathogenic amoebae. This clone was used for the identification of a homologous clone (cEH-NP1) in the cDNA from nonpathogenic amoebae. Sequence analysis and comparison of the predicted amino acid sequences for both clones disclosed 12% evolutionary divergence in structure. Hybridization of both cDNA probes to genomic DNA from four pathogenic and five nonpathogenic E. histolytica isolates revealed two distinct Southern blot patterns, one characteristic for pathogenic amoebae and the other for nonpathogenic amoebae. Further, the complex pattern of restriction fragments hybridizing to an actin cDNA probe was also different between pathogenic and nonpathogenic isolates but was conserved within each group of amoebae. The results indicate that pathogenic isolates of E. histolytica are genetically distinct from nonpathogenic isolates.