Pentatrichomonas intestinalis

Non-pathogenic, cosmopolitan parasite. It does not have a cystic stage: the vegetative form can survive for at least 24 hours in the environment and this enables its transmission.


Pentatrichomonas intestinalis lives in the large intestine (colon, caecum) where it reproduces by binary fission. The active vegetative form moves in a jerky, progressive, but non-directional manner. As for other flagellates, when the trophozoite immobilizes, it becomes round.

Size: 10-15 μm long, 7-10 μm wide.

Morphology: tear-dropped shaped. The nucleus, located at the larger anterior end, contains a small karyosome; peripheral chromatin is distributed unevenly over the nuclear membrane. Beside the nucleus is the cytostome, a small groove that is barely visible.

Flagella: 3-5 long, anteriorly directed, flagella originate from a group of blepharoplasts in front of the nucleus. One more flagellum is posteriorly directed and constitutes, with the body of the parasite, a long, folded, undulating membrane (plissée). This flagellum extends way beyond the posterior end of the trophozoite as a free flagellum. An axostile, a rigid support structure, runs longitudinally along the entire length of the parasite and extends from the back with a pointed end.

Within the cytoplasm are food vacuoles containing ingested bacteria and yeast. A typical feature of Pentatrichomonas intestinalis is represented by dark granules about 1 μm long, called hydrogenosomes: such structures can be seen with trichrome but not with Giemsa’s or May-Grünwald-Giemsa’s stains (which, besides, do not always stain flagella and the undulating membrane).