GROSS?

BACTERIA

One of our kingdoms

BACTERIABacteria are minute microscopic prokaryotes. They are unicellular organisms, which are usually identified by their specific activities, more than their general organization.

Bacteria are omnipresent, occurring in all environments.

The average size of bacterial cell ranges from 0.2 to 2.0 µm.

One way to classify bacteria is from its shape.

DIFFERENT FORMS OF BACTERIA

Cocci (singular coccus)

They are spherical in shape. They can be further distinguished into

Monococcus (occur singly)

Diplococcus (occur in pairs)

Tetracoccus (occur in groups of four)

Streptococcus (occur in the form of a filament) and

Staphylococcus (occur in the form of sheets).

Streptococcus pyogenes

Responsible of common infections including "strep throat" and skin infections

BACILLUS (RL- BACILLI)

They are straight, cylindrical, rod shaped bacteria. They may be further distinguished into

Monobacillus (single)

Diplobacillus (in pairs)

Streptobacillus (in filamentous form) and

Palisade Bacillus (in the form of a stack)

Bacillus anthracis

anthrax— a common disease of livestock and, occasionally, of humans.

SPIRILLUM

These bacteria are spirally coiled like

a corkscrew.

Lyme disease is caused by spirochetal bacteria from the genus Borrelia.

VIBRIO

These are elongated, C shaped or comma shaped bacteria.

Vibrio cholerae is a Gram-negative the cause of the cholera disease.

FLAGELLATION Most of the bacteria contain one to many locomotor structures called flagella.

Cocci do not have flagella. Based on the number and mode of attachment of the flagella, bacteria can be distinguished into the following types:

I . Atrichous : Bacteria without flagella. II. Trichous: They bear one or more flagella.

a) Monotrichous : Bacteria with a single flagellum, at one end b) Cephalotrichous : Bacteria with many flagella attached at one end

c) Amphitrichous : Bacteria with a single flagellum at each end d) Lophotrichous : Bacteria with a group of flagella attached at each end

e) Peritrichous : Bacteria with flagella all over the body

GRAM POSITIVE AND GRAM NEGATIVE

BACTERIA

In 1884 a Danish physician Christian Gram devised a technique of differential staining for bacterial cells, using two simple stains. The procedure involves staining bacteria initially with a weak alkaline solution of gentian (crystalline) violet. All bacterial cells stain blue with this dye. Subsequently these cells are treated with Lugol's iodine solution (Iodine in potassium iodide solution) and washed with alcohol. At this stage if the bacteria retain the purple colour, they are described as Gram positive bacteria and if they lose their purple colour, they are described as Gram negative bacteria. The Gram negative bacteria can be subsequently stained with saffranine for further investigations. The Gram positive and Gram negative bacteria show certain morphological and physiological differences between them.

GRAM STAINING

A Gram stain of mixed Staphylococcus aureus (Gram positive cocci) and Escherichia coli (Gram negative bacilli), the most common Gram stain reference bacteria

Gram (+)

Bacteria and humans