Classification On the basis Of shape
1. Cocci

Cocci are round or oval in shape. (singular coccus) 
For example miningococci and gonococci.
cocci are further classified in to following groups
 on the basis of their microscopic arrangement.
  • Diplococci: arranged in pairs
  • Streptococci: arranged in chains
  • Staphylococci: form grape like clusters.

2. Bacilli

Bacilli are rod shaped bacteria. Forexample E. coli,
Salmonela, C. Tatani. B. anthrax etc.
Spirochetes are spiral shaped they have flexible cell wall.
 for example, treponema, borrelia, laptospora etc.
4. Vibro
Vibro are comma shaped, for example vibro cholera 
and vibro vulnificus etc.
Classification On the basis Of Staining
1. Gram Positive
Gram positive bacteria are those which hold the crystal
 violet dye after being washed with the alcohol. They are
 stained dark purple in color. They have this
Property because they contain higher quantity of
 peptidoglycan in their cell wall
For example. Streptococci, Clostridium, Bacillus anthrax etc.
2. Gram Negative
Gram negative Bacteria lose the crystal violet dye when
they are washed with alcohol. Then the are counter stained
and give pink or red color in Gram staining technique.
For example E. coli, Salmonella Typhi. etc
3. Acid Fast

Acid Fast bacilli are those which hold the dye even after
 being washed with an acid. These bacteria are not stained 
by gram staining technique. These are stained 
Using special type of staining procedure called
 Zeihl Nelson Staining technique
Classification On the basis Of Temperature
1. Thermophiles

Thermophiles are those bacteira which grow
best in higher temperature. for example
Campylobacter jejuni which grows best at
42 degree centigrade.
2. Mesophiles

Mesophiles grow best at moderate temperature. many
bacteria belong to this group
3. Psychrophiles
Psychrophiles Grows best at lower temperature.
Classification On the basis Of Oxygen Requirement
1. Aerobes

Aerobes are those bacteria which can grow only
in the presence of normal concentration of oxygen
For example Mycobacterium Tuberculosis
2. Anaerobes

An aerobes are those bacteria which can grow only in
absence of Oxygen for example bacteroides.
3. Facultative 
These bacteria are capable of growing both in the presence
and absence of Oxygen for example E. coli
4. Micro-aero
These bacteria require extremely low concenteration of
Oxygen for their growth.
Classification On the basis Of Cell Wall
1. Thick Walled

These bacteria have thick cell wall for example
All gram positive and gram negative bacteria
2. Thin walled

these have thin flexible cell wall for example spirochetes
3. Wall less 
e.g Mycoplasma
Classification On the basis Of Spore Formation
1. Spore Forming

Aerobic: Bacillus Anthrax
Anerobic: Clostridium
2. Non Spore 
Forming Rods
Non Filamentous: Corynebacterium
Filamentous:          Listeria

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