The Protozoa

Mrs. Dalia Kamal Eldien

Msc in MicrobiologyLecture NO (2)

Objectives

Definition of protozoa Identification of their normal habitatMode of the reproduction Mode of nutrition Type of locomotion organelle Classification of protozoa (with examples to each

group)

Introduction

The parasites that infect humans can be grouped into three large groups: protozoa, helminths, and arthropods

Helminth is the common name used for parasitic worms. These include Trematodes (flukes), Cestodes (tapeworms), and Nematodes (roundworms). Most helminth infections occur in the intestinal tract

Arthropods include arachnids such as spiders, ticks, and mites, and insects such as lice, bugs, fleas, flies, and mosquitoes. Some arthropods, such as lice, fleas, and mosquitoes are parasitic to humans; others such as flies are important as vectors in transmitting the infective stages of parasites to humans.

Protozoa

Protozoa are single-celled eukaryotic organisms that are larger than most bacteria .

Protozoa(Profo=first +Zoon=animal) are the most primitive among the living animals

Most species are free living, but all higher animals are infected with one or more species of protozoa

Infections range from asymptomatic to life threatening, depending on the species and strain of the parasite and the resistance of the host.

StructureProtozoa are microscopic unicellular eukaryotes that

have a relatively complex internal structure including the Golgi apparatus, mitochondria, lysosomes, food vacuoles and other specialized structures

But according to many zoologists, it is not correct to designate protozoans as unicellular as they are complete organisms and not loose cells moving organs.

The body construction of some protozoa's may be more complicated than some of the simple metazoa.

Many protozoa alternate between a free-living vegetative form known as a trophozoite and a resting form known as a cyst.

 The protozoal cyst is somewhat analogous to the bacterial spore, since it resists harsh conditions in the environment.

Many protozoal parasites are taken into the body in the cyst form.

OccurrenceProtozoa prefer a moist habitat found in sea water,

fresh water and also in moist soil. They are ubiquitous and are found wherever nature

offers a damp surface.Many protozoa also occur in association with other

animals. The relationship may be mutualism, commensalism

or parasitism.

Reproduction Reproduce asexually as well as sexually, even though the

Principal means of multiplication is by asexual method. Asexual reproduction takes place by cell division. This is

of two types with respect to the number of daughter cells formed.

In binary fission two daughter cells are formed in multiple fission many daughter cells are formed.

Size and shape  Protozoa vary in size and shape. Smaller species may be the size of fungal cells larger species may be visible to the unaided eye.

Nutrition Protozoa are autotrophic(organisms that can produce their

own food from the substances available in their surroundings

using light (photosynthesis) or chemical energy

(chemosynthesis) or heterotrophic (cannot synthesize their

own food and rely on other organisms — both plants and

animals — for nutrition. )

Most species obtain large food particles by phagocytosis

Phagocytosis:  means  the local infolding of the cell's

 membrane and the protrusion of its cytoplasm around the

 fold until the material has been surrounded and engulfed

by closure of the membrane and formation of a vacuole

Some species have specialized structures called

cytostomes, or cell mouth, is a part of a cell

specialized for phagocytosis Food vacuoles are concerned with the ingestion and

digestion of food.

Food is digested by the activity of the enzymes produced

by lysosomes then digest the nutrients in the particle, and

the products of digestion are distributed throughout the cell.

Lysosomes are formed in the region of the golgi bodies.

phagocytosis

locomotion Many protozoal species move independently by one of

three types of locomotors organelles: pseudopodia flagella, and cilia

Pseudopodia (false foot) Are characteristic of amoebae, where the cytoplasm

forms temporary projections in the direction of movement.

The pseudopodia also help in the trapping of food.

Amoeba with pseudopodia

Flagella: Are long fibrous extensions of the cell and are

permanent features of the cell. The number of flagella per cell varies from one to many. The flagellum has two parts - a central filament

(axoneme) and a surrounding contractile sheath.Cilia Are fine short threads that extend from the body surface. All cilia in a cell may be of the same length or may vary. Cilia not only help in locomotion but also in driving the

food towards the oral grove

Flagellated protozoa

Ciliated protozoa

The classification of protozoa

Protozoa are categorized according to their method of movements:-

Flagellates – three of the most common and medically significant include: Giardia lamblia, Trypanosome sp. and Trichomonas vaginalis

Amoeba –include the pathogenic amoeba Entamoeba and Endolimax which cause dysentery in humans

Ciliates – the only parasitic ciliate that causes disease in humans in Balantidium coli

Sporozoa (‘spore-formers’) were originally recognized not on the basis of their locomotion.

Giardia lamblia flagellates

Entamoeba histolytica

Balantidium .coli

The basic generally accepted practical classification of the medically important parasitic protozoa

Amoebae Entamoeba histolytica Acanthamoeba species Naegleria species Flagellates Giardia lamblia Trichomonas vaginalis Trypanosoma species Leishmania species Ciliates Balantidium coli

Coccidia Blood and tissue coccidia:o Plasmodium specieso Toxoplasma gondii Intestinal coccidia:o Isospora bellio Cryptosporidium parvumo Cyclospora cayetanensis Microsporidia Encephalitozoon species Enterocytozoon species