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38 CHAPTER 3

Morphology reproduction occurs by binary fission. Cysts may form
in the lumen of the colon for infecting other hosts. The
This organism called B. coli is rather large and is covered trophozoite form of a protozoan is a stage where the
peripherally on the entire circumference of the cell by organism is motile and is able to feed during this phase of
short cilia. The trophozoite stage may vary in size from development (Figure 3-2). The trophozoite is unable to
30 to 120 μm by 30 to 80 μm, and some larger versions infect a human or other animal but is able to reproduce
may reach a size of 90 to 120 μm by 60 to 80 μm. The by division in the host and is capable of causing damage
trophozoite is tapered at the anterior portion with an to tissue in the infected individual.
attached cytostome. Two nuclei are visible, with a large
kidney bean–shaped macronucleus and a small nucleus
called the micronucleus. The cyst form is elliptical in MICROSCOPIC DIAGNOSTIC
shape and measures from 45 to 65 μm. Food vacuoles
are visible in the cytoplasm and a small opening at the FEATURE
posterior of the organism is used for waste elimination.
General
Symptoms Classification Protozoan, Ciliated

In some cases, infection with B. coli may result in few Organism Balantidium coli
or no symptoms. Balantidiasis due to infection with Specimen Required Stool specimen
B. coli causes generalized symptoms and signs includ- Stage Cyst or trophozoite
ing chronic and recurrent diarrhea, abdominal pain and Size Cyst = 45–75 μm; tro-
cramping, vomiting, weakness, and weight loss. phozoite (two ranges;
45 × 60 μm × 30–40 μm
and 90–120 μm ×
Life Cycle 60–80 μm)
The ciliate called Balantidium coli is chiefly contracted Shape Oval
from contaminated water and food, particularly where Motility Cilia in rotary motion
contact with animals occurs. The cyst is the infective for trophozoites
form of Balantidium coli, as is the case for most pro- Nucleus(i) 2 (kidney bean–
tozoans (Figure 3-1), and the host is infected by inges- shaped and a smaller,
round micronucleus)
tion of the infective cysts through water and food. In the
cyst form, protozoans are characterized by a thick pro- Cytoplasm Food vacuoles
tective membranous wall that makes them impervious Other Features One of larger proto-
to unfavorable environmental conditions. Excystation zoa; periphery com-
pletely covered by
(hatching from cyst) occurs in the small intestine and
short cilia
Balantidium coli Cyst
Source: Centers for Disease Control and Prevention (CDC)
Trophozoite

FIGURE 3-1 A cyst form of Balantidium coli Delmar/Cengage Learning