Entamoeba hartmanni
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p597-598
2025-09-23
182
General Characteristics
The life cycle of E. hartmanni is similar to that of E. dispar, with differences in size (Figures 1 and 2). In wet preparations, E. hartmanni trophozoites range in size from 4 to 12 µm in diameter, and cysts range in size from 5 to 10 µm in diameter. On the permanent stained smear, the cysts, primarily, tend to shrink as a result of dehydration; therefore, the sizes of all the organisms, including pathogenic E. histolytica, may be somewhat smaller (1 to 1.5 µm) than the wet preparation measurements.
Fig1. A, Entamoeba hartmanni trophozoite. B, E. hartmanni
Fig2. A to C, Trophozoites of Entamoeba hartmanni. D and E, Cysts of E. hartmanni.
Trophozoites do not ingest RBCs, and the motility is usually less rapid (see figure 1, and 2). The morphologic characteristics of E. hartmanni are very similar to those of E. histolytica, with two exceptions. Frequently, E. hartmanni cysts may contain only one or two nuclei, even though the mature cyst contains four nuclei. Mature cysts of E. hartmanni also retain their chromatoidal bars, a characteristic not usually seen in E. histolytica/E. dispar. E. hartmanni’s chromatoidal bars are similar to those of E. histolytica and E. dispar but smaller and more numerous (see Figures 1 and 2). At the species level, differentiation between E. hartmanni and E. histolytica/E. dispar depends on size; therefore, laboratories are required to use calibrated microscopes that are checked periodically for accuracy.
Epidemiology
Transmission occurs through the ingestion of mature cysts from contaminated food or water. If accurate identifications have been recorded, the colonization rate tends to match that of E. histolytica.
Pathogenesis and Spectrum of Disease
E. hartmanni is considered nonpathogenic and does not cause disease.
Laboratory Diagnosis
Unless the trophozoites and cysts match the size requirements, they are unlikely to be E. hartmanni. Definitive identification relies on examination of permanent stained smears and measurements made with the calibrated microscope.
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