RESUMO
Entamoeba histolytica causes amebic colitis and liver abscess in developing countries such as Mexico and India. Entamoeba dispar is morphologically identical but is not associated with disease. Here we determined the ploidy of E. histolytica and developed PCR-based methods for distinguishing field isolates of E. histolytica or E. dispar. Fluorescence in situ hybridization showed that E. histolytica trophozoites are diploid for five "single-copy" probes tested. Intergenic sequences between superoxide dismutase and actin 3 genes of clinical isolates of E. histolytica from the New and Old Worlds were identical, as were those of E. dispar. These results suggest a bottleneck or demographic sweep in entamoebae which infect humans. In contrast, E. histolytica and E. dispar genes encoding repeat antigens on the surface of trophozoites (Ser-rich protein) or encysting parasites (chitinase) were highly polymorphic. chitinase alleles suggested that the early axenized strains of E. histolytica, HM-1 from Mexico City, Mexico, and NIH-200 from Calcutta, India, are still present and that similar E. dispar parasites can be identified in both the New and Old Worlds. Ser-rich protein alleles, which suggested the presence of the HM-1 strain in Mexico City, included some E. histolytica genes that predicted Ser-rich proteins with very few repeats. These results, which suggest diversifying selection at chitinase and Ser-rich protein loci, demonstrate the usefulness of these alleles for distinguishing clinical isolates of E. histolytica and E. dispar.
Assuntos
Entamoeba/genética , Entamebíase/epidemiologia , Actinas/genética , Sequência de Aminoácidos , Animais , Proteínas de Bactérias/genética , Sequência de Bases , Quitinases/genética , Demografia , Diploide , Entamoeba/citologia , Entamoeba histolytica/citologia , Entamoeba histolytica/genética , Humanos , Hibridização in Situ Fluorescente , Índia/epidemiologia , Íntrons , México/epidemiologia , Epidemiologia Molecular , Dados de Sequência Molecular , Reação em Cadeia da Polimerase/métodos , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , SerinaRESUMO
E. histolytica parasites in Mexican children's stools were identified and typed as pathogenic or non-pathogenic using the polymerase chain reaction (PCR) and nonradioactive probes. PCRs were performed with primers specific for 145 base pair (bp) pathogenic or 133 bp non-pathogenic DNA sequences, which are highly repeated in E. histolytica parasites with pathogenic or non-pathogenic isoenzyme patterns, respectively. Dot-blotted PCR products were identified with a horseradish peroxidase-conjugated oligonucleotide probe specific for either the 145 bp pathogenic or 133 bp non-pathogenic sequences. The PCR and the 145 bp pathogenic probe correctly identified eight cultures with pathogenic isoenzyme types and none of nine cultures with non-pathogenic isoenzyme. The PCR and 133 bp non-pathogenic probe identified all of the non-pathogenic cultures, none of the axenized pathogenic cultures, and three of five xenic cultures with pathogenic isoenzymes. The two probes together identified all 49 stools containing E. histolytica by light microscopy (sensitivity = 1.0), which represented the entire set of the E. histolytica-positive stools diagnosed at the Hospital Infantil over a 10 week period. Most patient isolates were positive with both 145 bp pathogenic and 133 bp non-pathogenic probes, suggesting that these children, 60% of whom were dysenteric, are infected with mixed populations of amebas.