Lesson 2: Public Health Microbiology

Section V: Protozoa

2-21

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Section V. PROTOZOA

2-21. GENERAL

Protozoa are minute, unicellular organisms belonging to the Animal Kingdom Protista. They range in size from nearly submicroscopic 100u; however, the vast majority of them are microscopic. Thousands of species have been identified, but relatively few are pathogenic to man.

a. Morphology. Protozoa vary widely in structure. Some have organelles of locomotion--flagella, cilia, or pseudopods. Some have definite openings to absorb food. All consist of one or more nuclei and cytoplasm. Many have various inclusion bodies.

b. Physiology.

(1) Nutrition. Most protozoa absorb fluid directly through the cell membrane. Many can take in solid food and digest it by enzymes produced by their own cytoplasm.

 

(2) Reproduction. Protozoa multiply species, and by sexual reproduction in others. of sexual and asexual reproduction.

 

(3) Locomotion. Nearly all protozoa possess some means of locomotion. Some have flagella (figure 2-6); others have cilia (delicate, hair-like organelles); and some have pseudopods (false feet), which are protoplasmic processes that flow forward in a manner similar to the action of a balloon partially filled with liquid, pulling the cell along with them.

 

(4) Cyst formation. Many protozoa have the ability to form cysts when subjected to an unfavorable environment. This process is similar to spore formation in bacteria. Since protozoan cysts are much more resistant to unfavorable environmental conditions than are the vegetative forms, the cysts are responsible for the transmission of most protozoan infections.

 

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