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).

3

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.

6

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.

9

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.

12

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

24

• 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

25