Lecture notes Microbiology 1

Chapter 5


BACTERIA



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, 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)
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, 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.

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, 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




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