Presence of ingested RBCs is a characteristic feature of

The correct option is Entamoeba histolytica.

To understand why this is the correct answer, let's break down the biological characteristics of the organism and the significance of ingested red blood cells (RBCs):

1. Understanding Erythrophagocytosis:
Erythrophagocytosis refers to the ingestion of red blood cells (erythrocytes) by another cell. In parasitology, finding amoebic trophozoites with ingested RBCs in their cytoplasm is a crucial diagnostic indicator.

2. Pathogenic vs. Non-Pathogenic Amoebae:
Among the intestinal amoebae listed in the options:
- Entamoeba histolytica is a well-known pathogen capable of invading tissues (histolytic means tissue-dissolving). It secretes enzymes that destroy host tissues, leading to mucosal ulcers, and actively ingests host red blood cells for nutrition during invasive disease (amoebic dysentery).
- Entamoeba coli, Dientamoeba fragilis, and Iodamoeba bütschlii are generally non-invasive commensal organisms. While they ingest bacteria and other debris in the intestinal lumen, they do not typically ingest red blood cells because they do not invade tissue or cause mucosal hemorrhages in the same manner as E. histolytica.

3. Diagnostic Significance:
In microscopic examinations of stool specimens, the presence of trophozoites containing ingested RBCs (erythrophagocytosis) is considered a pathognomonic feature that specifically distinguishes the pathogenic Entamoeba histolytica from the morphologically identical but non-pathogenic commensal Entamoeba dispar.