Assistant professor in microbiology Protozoa BMS 241 Lecture (1) By Dr.Dalia M. Mohsen Assistant professor in microbiology

Introduction Protozoa: [s., protozoan; Greek protos, first, and zoon, animal] A protozoan can be defined as a usually motile, eukaryotic, unicellular protest. the most important groups are the: Flagellates, Amoebae, Ciliates.

Distribution Protozoa grow in a wide variety of moist habitats. Most protozoa are free living and inhabit Fresh water or marine environments. Many terrestrial protozoa can be found in decaying organic matter, in soil, and even in beach sand; some are parasitic in plants or animals.

Morphology Because protozoa are eukaryotic cells, in many respects their morphology and physiology are the same as the cells of multicellular animals .

Morphology Ectoplasm: some morphological and physiological features are unique to protozoan cells. Ectoplasm: In some species the cytoplasm immediately under the plasma membrane is semisolid or gelatinous, giving some rigidity to the cell body. It is termed the ectoplasm. The bases of the flagella or cilia and their associated fibrillar structures are embedded in the ectoplasm.

Morphology Endoplasm: Inside the ectoplasm is the area referred to as the endoplasm, which is more fluid and granular in composition and contains most of the organelles.

Morphology Nuclues: Some protozoa have one nucleus, others have two or more identical nuclei.

Morphology The vacuoles: One or more vacuoles are usually present in the cytoplasm of protozoa. These are differentiated into: Contractile vacuoles. Secretory vacuoles. Phagocytic vacuoles.

Morphology contractile vacuoles: function as osmoregulatory organelles in those protozoa. Secretory vacuoles: usually contain specific enzymes that perform various functions. Phagocytic vacuoles: the sites of food digestion.

Encystment Many protozoa are capable of encystations. They develop into a resting stage called a cyst. Cyst : Is a dormant form marked by the presence of a wall and by very low metabolic activity. Cyst formation is particularly common among aquatic, free-living protozoa and parasitic forms.

Encystment Cysts functions: They protect against adverse changes in the environment, such as nutrient deficiency, pressure of O2.

Excystment Although the exact stimulus for excystation (escape from the cysts) is unknown, excystation generally is triggered by a return to favorable environmental conditions. For example, cysts of parasitic species excyst after ingestion by the host and form the vegetative form called the trophozoite.

Locomotory Organelles A few protozoa are nonmotile. Most, however, can move by one of three major types of locomotory organelles: pseudopodia, flagella, or cilia.

Locomotory Organelles Pseudopodia: [s., pseudopodium; false feet] Are cytoplasmic extensions found in the amoebae that are responsible for the movement and food capture. There are many types of pseudopodia: Flagellates move by flagella Ciliates move by cilia. protozoan flagella and cilia are structurally the same and identical in function to those of other eukaryotic cells.

Reproduction Type of protozoa reproduction: A sexual reproduction: binary fission: During this process the nucleus first undergoes mitosis, then the cytoplasm divides to form two identical individuals.

Reproduction Sexual reproduction: Conjugation: In this process there is an exchange of gametes between paired protozoa of complementary mating types.

Transmission of Protozoa Transmission from one host to another within a cyst. Pathogenic protozoa can spread from one infected person to another by: Faecal – oral transmission of contaminated foods and water. Insect.

Pathogenesis of protozoa Protozoan have numerous ways to enter the body of the human host Factors that are important for pathogenecity include: Attachment to the host tissue followed by replication to establish colonization. Toxic products released by parasitic protozoa. Shifting of antigenic expression to evade the immune response and inactivate hostdefences.

Antiprotozoal agents Antiprotozoal agents Generally the antiprotozoal agents target relatively rapidly proliferating, young, growing cells of the parasite. Most commonly, these agents target nucleic acid synthesis, protein synthesis, or specific metabolic pathways (e.g. folate metabolism) unique to the protozoan parasites..

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