Bacteria are classified into five groups according to their basic shapes:
1.spherical shape (cocci) :
e.g Staphylococcus aureus grows best in an aerobic environment but it can also live in anaerobic conditions (without oxygen).
2.rod shape (bacilli):
3. spiral (spirilla) :
4.comma (vibrios) or corkscrew (spirochaetes):
They can exist as single cells, in pairs, chains or clusters.
Microorganisms can be classified according to their oxygen requirements necessary for growth and survival:
Obligate Aerobes: (oxygen required)
Facultative: (grow in the presence or absence of oxygen)
Microaerophilic: (grow best at very low levels of oxygen)
Aerotolerant Anaerobes: (oxygen not required for growth but not harmful if present)
Obligate Anaerobes: ( grow only in complete absence of oxygen; if present it can be lethal)
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