Chapter 5
BACTERIA
1
, Introduction
Bacteria are prokaryotic organisms (Please refer to
Chapter 2: Domains of Life)
Beneficial (good) bacteria:
•Used in food processing (e.g. cheese and yoghurt)
•Degrade environmental pollutants (chemicals)
•Contribute to gut (digestive) health in mammals
Non-beneficial (bad) bacteria:
•Causes infections in humans (e.g. ear infection; eye
infection)
•Causes illness in humans and animals (e.g. Tuberculoses
(Mycobacterium tuberculosis); digestive illness
(Staphylococcus aureus)
2
, Bacteria
Different species are differentiated by factors
such as:
Morphology (shape).
Chemical composition of cell wall (detected by
staining, i.e. Gram-staining).
Nutritional requirements (e.g. carbon and nitrogen
source).
DNA sequence.
3
, Bacterial sizes and shapes
Bacteria size ranges from 0.2 to 2.0 µm (micrometers) in diameter
and 2-8 µm in length
Cell shapes:
Coccus (spherical) - (plural: cocci)
Bacillus (rod shaped) – (plural:bacilli).
Coccobacillus – (Shape intermediate between coccus and bacillus)
Spiral – (spirilla – helical rigid shape)
Spiral - (spirochetes – helical flexible shape)
Vibrio (gentle curve)
Pleomorphic – vary in shape
4
BACTERIA
1
, Introduction
Bacteria are prokaryotic organisms (Please refer to
Chapter 2: Domains of Life)
Beneficial (good) bacteria:
•Used in food processing (e.g. cheese and yoghurt)
•Degrade environmental pollutants (chemicals)
•Contribute to gut (digestive) health in mammals
Non-beneficial (bad) bacteria:
•Causes infections in humans (e.g. ear infection; eye
infection)
•Causes illness in humans and animals (e.g. Tuberculoses
(Mycobacterium tuberculosis); digestive illness
(Staphylococcus aureus)
2
, Bacteria
Different species are differentiated by factors
such as:
Morphology (shape).
Chemical composition of cell wall (detected by
staining, i.e. Gram-staining).
Nutritional requirements (e.g. carbon and nitrogen
source).
DNA sequence.
3
, Bacterial sizes and shapes
Bacteria size ranges from 0.2 to 2.0 µm (micrometers) in diameter
and 2-8 µm in length
Cell shapes:
Coccus (spherical) - (plural: cocci)
Bacillus (rod shaped) – (plural:bacilli).
Coccobacillus – (Shape intermediate between coccus and bacillus)
Spiral – (spirilla – helical rigid shape)
Spiral - (spirochetes – helical flexible shape)
Vibrio (gentle curve)
Pleomorphic – vary in shape
4
