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General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025
4- Osmotic pressure
Bacteria can be classified based upon the salinity they can tolerate:
1- Halophiles
Microorganisms that require some NaCl for growth
➢ Mild halophiles: require 1-6% salt
eg: Most bacteria in oceans.
➢ Moderate halophiles: require 6-15% salt
➢ Extreme Halophiles: require very high salt (15 to
30%).
eg: Bacteria in Dead Sea.
2- Osmotolerant (halotolerant)
Bacteria that are able to grow at moderate salt concentrations, even though they
grow best in the absence of NaCl, are called halotolerant
eg. Staphylococcus aureus
3- Non-halophiles:
Bacteria that prefer low salt concentrations, grow best in media containing less
than 0.2 M salts
eg. E. coli
4- Xerophiles
They grow in dehydrated environments.
General Microbiology & Immunology (PM 401) theoretical handbook Page 48
