Balantidium coli - Introduction, Classification, History, Habitat, Morphology, Culture

Introduction of Balantidium coli

Balantidium coli are exclusive parasites of the vertebrate and invertebrate hosts inhabiting their digestive tract. They multiply by binary fission while their sexual cycle takes place by conjugation.

Balantidium coli is the only species in the genus Balantidium which is pathogenic to humans. Also, it is the largest human protozoa parasite.

Balantidium coli are oval in shape with conspicuous cytostome, contractive vacuoles, two nuclei (large bean-shaped macronucleus and minute micronucleus), and cilia over their body.

Classification of Balantidium coli

The classification of Balantidium coli is as follows

Kingdom: Chromista

Superphylum: Alveolata

Phylum: Ciliophora

Class: Litostomatea

Order: Vestibuliferida

Family: Balantidiidae

Genus: Balantidium

Species: B. coli

History of Balantidium coli

The human protozoa parasite was first described in 1857 by Malmsten in the feces of a man suffering from dysentery and named it Paramecium coli. It was later named Balantidium coli by Stein in 1863.

Habitat of Balantidium coli

Balantidium coli inhabits the intestine of humans, pigs, and monkeys.

Morphology of Balantidium coli

The morphological stages of Balantidium coli include trophozoite and cyst.

Trophozoite

• trophozoites are the invasive form of Balantidium coli

• size varies from 30 μm to 300 μm in length and 30 μm to 100 μm in breadth

• oval-shaped with a slightly pointed anterior end while the posterior end is rounded

• Balantidium coli motility takes place with the help of rows of tiny cilia which covers the entire surface of the body

• conspicuous V-shaped mouth called cytostome present at the anterior end

• cytostome leads to the cytopharynx which is a funnel-shaped guller extending up to one-third of the body

• a less prominent pore called cytostome is present at the posterior end of the parasite

• cytostome function is to evacuate the contents of food molecules

• two nuclei (large bean-shaped macronucleus and minute micronucleus) are present

• micronucleus lies on the concavity of the macronucleus

• numerous food vacuoles and two contractile vacuoles are also present

• the trophozoite of Balantidium coli feeds on bacteria, erythrocytes, and fat droplets

Cyst

• Balantidium coli cysts are resistant form as well as the infective form

• round in shape

• cysts are smaller than trophozoites

• measures 40 μm to 60 μm in diameter

• a cyst is surrounded by a cyst wall which is thick and transparent

• like trophozoite form, the Balantidium coli cyst also contains two nuclei (large bean-shaped macronucleus and minute micronucleus) and the micronucleus lies on the concavity of the macronucleus

• granular cytoplasm has a refractile body and numerous food vacuoles

• cilia may be present in younger cysts but are absent in mature ones

Culture of Balantidium coli

In media

Balantidium coli can be grown in Robinson’s medium. Culture media used for in-vitro culture of Entamoeba histolytica.

NIH Polyxenic culture

• created by Boeck and Drbohlav in 1927

• contains the egg-serum medium with Lock’s medium and bacterial flora (polyxenic or polybacterial culture) which will provide nourishment for the growing parasites

• other cultures such as Balamuths, Nelsons, or Robertsons’ media can also be used to isolate the parasite from the stool

Axenic Culture

• this bacteria-free culture was first created by Diamond in 1961

• useful for:

  studying the pathogenicity of protozoa

  test anti-parasite drugs in vitro

  study immunological property

  prepare axenic amoebic antigens for immunodiagnosis