Protozoa are the largest of the unicellular true microorganisms. They are classified in the Kingdom Protista although their name implies that they were the forerunners of the animal kingdom (proto = first; zoa = animal).

The basic structures of all protozoa include a nucleus well defined by a nuclear mem brane, lying within cytoplasm that is enclosed by a thin outer cell membrane. Other specialized structures, such as cilia or flagella (see colorplate 49) for locomotion or a gullet for food intake, vary with different types of protozoa. Six major groups of protozoa are distinguished on the basis of their locomotory structures or their reproductive mechanisms (see fig. 32.1).

Amebae. Simple ameboid forms. Move by bulging and retracting their cytoplasm in any direction. Major pathogen is Entamoeba histolytica (see colorplate 50).

Ciliates. Move by rapid beating of cilia (fine hairs) that cover the cell membrane. Balantidium coli is a protozoan ciliate that may cause human disease.

Flagellates. Possess one or more flagella that give them a lashing motility. Giardia lamblia (see colorplate 51), Trichomonas vaginalis (see colorplate 49), and the trypanosomes are the major pathogens in this group.

Apicomplexa. No special structures for locomotion (some immature forms have ameboid motility). Reproductive cycle includes both immature and mature forms (later called sporozoites). Toxoplasma gondii and Plasmodium species (see colorplate 52), which are the malarial parasites, are the representative pathogens in this group.

Coccidia. Represent a subphylum of the Apicomplexa. Coccidia have a complex life cycle in which all stages of parasite development are intracellular. Major genera include Cryptosporidium (see colorplate 53), Cyclospora, and Isospora.

Microspora. Includes a large group of obligate, intracellular protozoa that produce spores. These protozoa are classified in more than 100 genera and 1,200 species, collectively called microsporidia. Major genera causing human disease are Enterocytozoon, En-cephalitozoon, Nosema, and Pleistophora.

Diagramatic examples of the amebae, ciliates, flagellates, and the Apicomplexa are shown in figure 32.1.

As indicated, species from each of these protozoan groups are associated with human diseases. Some of them are carried into the body through the gastrointestinal tract (in contaminated food or water or by direct fecal contamination of objects placed in the mouth), localize there, and produce diarrhea or dysentery. Others are carried by arthropods, which inject them into the body when they bite. This group of protozoa then infects the blood and other deep tissues. The pathogenic protozoa are summarized in table 32.1.

It should also be noted that some of the intestinal protozoa may live normally in the bowel without causing damage under ordinary circumstances. Some flagellated protozoa frequently are found on the superficial urogenital membranes and sometimes are troublesome when they multiply extensively and irritate local tissues.

Morello-Mizer-Granato: I III. Diagnostic I 11. Microbial Pathogens I I © The McGraw-Hill

Laboratory Manual and Microbiology in Action Requiring Special Companies, 2003

Workbook in Microbiology, Laboratory Techniques 7/e

Figure 32.1 Diagrams of four types of protozoa. (a) An active ameba. (b) A ciliated protozoan (Balantidium coli), (c), (d), and

(e) Three types of flagellated protozoa. (f) Developmental stages of the malarial parasite, a sporozoan (Plasmodium species).

Figure 32.1 Diagrams of four types of protozoa. (a) An active ameba. (b) A ciliated protozoan (Balantidium coli), (c), (d), and

(e) Three types of flagellated protozoa. (f) Developmental stages of the malarial parasite, a sporozoan (Plasmodium species).

Types Protozoan Parasites
Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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  • zack
    What are the four types of disease causing protozoa?
    6 years ago
  • ronja
    What is the gullet in balantidium coli?
    6 years ago

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