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PROTOZOA
COURSE : B.SC. (MICRO)
SUBJECT: ELEMENATRY MICROBIOLOGY
UNIT 3.4
1
Protozoa
• Diverse group defined by three characteristics
– Eukaryotic
– Unicellular
– Lack a cell wall
• Motile by means of cilia, flagella, and/or pseudopodia
– Except subgroup, apicomplexans
© 2012 Pearson Education Inc.2
Unicellular, chemoheterotrophic, eukaryotic organisms of kingdom Protista (3-2000 mm).
Protozoan - “first animal”.
20,000 species, only a few are pathogens.
Most are free-living organisms that inhabit water and soil. Some live in association with other organisms as parasites or symbionts.
Reproduce asexually by fission, budding, or schizogony.
Some exhibit sexual reproduction (e.g.: Paramecium).
Trophozoite: Vegetative stage which feeds upon bacteria and particulate nutrients.
Cyst: Some protozoa produce a protective capsule under adverse conditions (toxins, scarce water, food, or oxygen).
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V. PROTOZOA (Continued)
Nutrition Most are heterotrophic aerobes. Intestinal protozoa can
grow anaerobically.Some ingest whole algae, yeast, bacteria, or smaller
protozoans. Others live on dead and decaying matter. Parasitic protozoa break down and absorb nutrients from their hosts.
Some transport food across the membrane. Others have a protective covering (pellicle) and required
specialized structures to take in food.– Ciliates take in food through a cytostome.
Digestion takes place in vacuoles.Waste may be eliminated through plasma membrane or an
anal pore.
4
Medically Important Protozoa
1. Amoeboflagellates (Phylum Sarcomastigophora)
Move using pseudopods (false feet) or flagella.
A. Amoebas (Subphylum Sarcodina)
Move by extending blunt, lobelike projections (pseudopods).
Amoebas engulf food with pseudopods and phagocytize it.
Several species cause amoebic dysenteries of varying degrees of severity.– Entamoeba hystolytica: Feeds on red blood cells. Produces
dysentery and extraintestinal cysts.
– Dientamoeba fragilis: Found in 4% of humans. Usually commensal. Can cause chronic, mild diarrhea.
Other diseases include:– Meningoencephalitis: Caused by Naegleria fowleri. Penetrate
nasal mucosa of swimmers in warm waters. Mortality rate almost 100%.
– Keratitis: Caused by Acanthamoeba. Can cause blindness. Associated with use of contact lenses. 5
B. Flagellates (Subphylum Mastigophora)
Move by one or more whiplike flagella. Some parasitic flagellates have up to eight flagella.
Most are spindle shaped with flagella projecting from anterior end.
Outer membrane is a tough pellicle. Food is ingested through an oral groove or cytosotome.
Important pathogens:– Trichomonas vaginalis: Causes genital and urinary infections. Has
undulating membrane. Lacks a cyst stage. Transmitted sexually or by fomites.
– Giardia lamblia: Causes a persistent intestinal infection (giardiasis) with diarrhea, nausea, flatulence, and cramps. In U.S. most common cause of waterborne diarrhea. About 7% of U.S. population are healthy carriers.
– Trypanosoma brucei gambiense: Hemoflagellate (blood parasite). Causes African sleeping sickness.
– Trypanosoma cruzi: Hemoflagellate that causes Chaga’s disease, a cardiovascular disease common in Texas and Latin America.
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V. PROTOZOA (Continued)
Nutrition Most are heterotrophic aerobes. Intestinal protozoa can
grow anaerobically.Some ingest whole algae, yeast, bacteria, or smaller
protozoans. Others live on dead and decaying matter. Parasitic protozoa break down and absorb nutrients from their hosts.
Some transport food across the membrane. Others have a protective covering (pellicle) and required
specialized structures to take in food.– Ciliates take in food through a cytostome.
Digestion takes place in vacuoles.Waste may be eliminated through plasma membrane or an
anal pore.
7
Life Cycle of Plasmodium spp. the Infectious Agent of Malaria
81
Medically Important Protozoa (Continued)
3. Ciliates (Phylum Ciliophora)
Move and obtain food using cilia.
Only known human pathogen is Balantidium coli, which
causes a severe intestinal infection in pigs and humans.
4. Microsporans (Phylum Mycrospora)
Obligate intracellular parasites, lack mitochondria and
microtubules.
Discovered in 1984 to cause chronic diarrhea and
conjunctivitis, mainly in AIDS patients.
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Paramecium caudatum is a Ciliated ProtozoanConjugation Between Opposite Mating Strains
102
VI. HELMINTHS (WORMS)
Characteristics
Eukaryotic, multicellular animals that usually have
digestive, circulatory, nervous, excretory, and reproductive
systems.
Worms with bilateral symmetry, head and tail, and tissue
differentiation (endoderm, mesoderm, and ectoderm).
Parasitic helminths spend most or all of their lives in host
and usually have the following specializations:
– May lack a digestive system. Absorb nutrients from host’s food,
body fluids, or tissues.
– Have a reduced nervous system.
– Means of locomotion is reduced or absent.
– Complex reproductive system. Individuals produce many eggs that
can infect another host. 11
VI. HELMINTHS (Continued)
Two main groups (phyla)Platyhelminths (Flatworms)Nematoda (Roundworms) Life CycleExtremely complex Intermediate hosts harbor larval (developmental) stage.Definitive host harbors adult stage.Sexual reproduction strategies:
– Dioecious: Male and female reproductive organs are found in
separate individuals.
– Monoecious (Hermaphroditic): One animal has both male and
female sex organs. Most hermaphrodites copulate with other
animals, a few copulate with themselves.
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Free-Living Flatworm Life Cycle of Blood FlukePlanaria (Schistosoma)
133
Cestode (Tapeworm) Body Structure:Scolex and Proglottids
144
VI. HELMINTHS (Continued)
II. Nematodes (Roundworms)
Cylindrical body tapered at each end.
Have a complete digestive system: mouth, intestine, and anus.
Body is covered by tough cuticle that resists drying and crushing.
Most species are dioecious: separate males and females.– Males are smaller than females and have one or two spicules on
posterior end.
Over 90,000 known species. Most are free-living. Only about 50 are human parasites.
Life cycle of parasitic nematodes is simpler than that of flatworms.
Infections can be caused by eggs or larvae.15
Comparison of Body Organization of Flatworms, Roundworms, and Earthworms
Flatworm
Earthworm
Roundworm
165
II. Nematodes (Roundworms) Continued
Infectious eggs– Pinworm (Enterobius vermicularis): Spends entire life in human
host. Adults live in large intestine. Female lays eggs in perianal region which causes itching. Up to 90% of children are infected through contaminated clothes or bedding. Infection usually disappears after a few years.
– Ascaris (Ascaris lumbricoides): Large nematode, up to 30 cm. Dioecious with sexual dimorphism. Live in small intestines of humans, horses, and pigs. Eggs can survive in soil for long time.
Infectious larvae– Adult Hookworm (Necator americanus): Live in small intestine of
humans, eggs are excreted in feces. Enter host by penetrating skin. Enters bloodstream, travels to lungs, swallowed in sputum. Avoided by wearing shoes.
– Trichinosis (Trichinella spiralis): Reproduce sexually in small intestine of humans. Obtained from eating undercooked pork. Larvae enter blood vessels and form cysts throughout body.
– Anisakines (Wriggly worms): Infected fish and squid. Killed by freezing and cooking.
17
Pinworm (Enterobius vermicularis)
186
Pinworm Eggs (Enterobius vermicularis)
197
Ascaris (Ascaris lumbricoides)
208
Head of Ascaris (Ascaris lumbricoides)
219
Arachnids are Arthropods with Eight Legs
Lyme Disease Vector Spotted Mountain Fever and Tularemia Vector
2210
Insects are Arthropods with Six Legs
Tse-tse Fly: Host Vector ofAfrican Sleeping Sickness
2311
Reference:
Images (1 to 5) : Microbiology by Gerard J. Tortora, Christine L Case, and Berdell R. Funke
Image 6: Source: http://www.biosci.ohio state.edu/~parasite/a-h.html
Image 7: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Image 8: http://www.biosci.ohio-state.edu/~parasite/a-h.html
Image 9: www. soton.ac.uk/~djab/ascaris.htmlImage 10: www. soton.ac.uk/~djab/ascaris.htmlImage 11: www. soton.ac.uk/~djab/ascaris.html
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• Books:1. Microbiology VI Edition, M.J. Pelczar, E.C.S. Chan
and N.R. Kreig, Tata McGraw Hill2. Brock Biology of Microorganisms (13th Edition)
by Michael T. Madigan, John M. Martinko, David Stahl.
3. Microbiology by Gerard J. Tortora, Christine L Case, and Berdell R. Funke
4. Microbiology by Prescott, Harley, and Klein's Microbiology Joanne M. Willey, Linda M
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