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Detailed Classification Of Bacteria - Microbiology


Classification On the basis Of Shape

1. Cocci 

Cocci are round or oval in shape. (singular coccus) 
For example meningococci and gonococci.
cocci are further classified into the 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. For example E. coli,
Salmonella, C. Tatani. B. anthrax etc.
Spirochetes are spiral shaped they have a flexible cell wall.
 for example, Treponema, Borrelia, leptospira etc.
4. Vibro
Vibro are comma-shaped, for example, Vibrio 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 colour. They have this
Property because they contain a 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 they are counterstained
and give a pink or red colour in the 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 acid. These bacteria are not stained by gram staining technique. These are stained 
Using a special type of staining procedure called
 Zeihl Nelson Staining technique

Classification On the basis Of Temperature

1. Thermophiles

Thermophiles are those bacteria 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 a lower temperature.

Classification On the basis Of Oxygen Requirement

1. Aerobes

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

Anaerobes are those bacteria which can grow only in the 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 an extremely low concentration 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
Anaerobic: Clostridium
2. Non-Spore 
Forming Rods
Non-Filamentous: Corynebacterium
Filamentous:          Listeria


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