Prof. Dr. Sevgi ERTUĞRUL KARATAY
Biochemical Tests
Usage Areas of Biochemical Tests Medicine
Food Microbiology
Environmental Microbiology Industrial Microbiology
Biotechnology
Purpose of Biochemical Tests
Isolation Definition Examination
Determination of Some Properties (enzyme activity, movement, etc.)
Biochemical Tests
Phenotypic tests.
The main purpose of these tests is to provide information about the metabolism or structural properties of the
microorganism with various indicators.
Biochemical Tests
Example: MacKonkey Agar is a selective medium especially for coliform bacteria and Escherichia coli. The bile salts and
crystal violet in the medium prevent the growth of Gram (+) bacteria and are used as selective indicator in the medium.
When lactose is used, a red color is formed due to the pH drop. As a result of degradation of bile acids, turbid zones
are formed.
For this reason, bacteria that use lactose are observed as red and those who do not use it as colorless.
Biochemical Tests
Mannitol salt agar is a selective medium for Staphylococcus aureus.
The high salt in this medium suppresses the growth of other microorganisms, while mannitol promotes the growth of S.
aureus.
In the medium, phenol red is found as an indicator and under certain pH values, the color of the medium changes from red to yellow. Therefore, colonies forming yellow zones on the red
medium are considered as S. aureus.
Biochemical Tests
Gives important ideas about
•Metabolism of microorganisms
•Fermentative pathways
•Gas production
• Enzyme activities etc.
Identification
One of the most important sources used for identification is the Bergey’s Manual.
In addition to biochemical tests, this resource is used for identification of microorganisms by taking
advantage of other main features of microorganisms.
