A bacteria contains an outer cell envelope which consists of: 1. Outer cell wall 2. Inner cytoplasmic membrane Cytoplasm is present inside the cell envelope. In the cytoplasm, there are inclu­sions such as ribosomes, granules, vacuoles and DNA. The bacte­rial cell as a whole may be enclosed in a capsule. Some bacteria may have flagellate which are used for locomotion and fimbriae which are used for adhesion. The flagella and fimbriae are ap­pendages which protrude from the cell surface.

CLASSIFICATION OF BACTERIA

1. Based on Gram staining

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Based on Gram staining, bac­teria can be differentiated into two groups: 1. Gram positive bacte­ria 2. Gram negative bacteria.

Some bacteria take up Gram stain, resist decolourisation and appear violet with this stain. They are called as Gram positive bacteria e.g. Streptococcus, Staphylococcus.

In some bacteria Gram stain is not taken up since it is decolorized by organic solvents. They take the counterstain and appear red. They are called as Gram negative bacteria e.g. Salmonella, Sheila.

2. Based on shape of bacteria

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Bacteria vary in their shape. Depending on the shape they are classified as:

 

1.

Cocci

spherical or oval cells

2.

Bacilli

rod shaped cells

3.

Vibrios

comma shaped curved rods

4.

Spirilla

rigid spiral forms

5.

Spirochetes

flexible spiral forms

6.

Actinomycetes

branching filamentous forms

7.

Mycoplasmas

cell wall deficient forms