Triple Sugar Iron Assay: Click Here to View Images
Triple sugar iron agar is used for a dual purpose. It can indicate both
carbohydrate fermentation, and hydrogen sulfide production. This test is
generally used to help identify enteric bacteria. In this procedure, bacteria
can be differentiated based on their pattern of utilization of several nutrients.
There are two parts to the test, the slant and the butt.
Tips for Success:
Examine the tubes at no earlier or later than 18-24 hours; otherwise, a false
positive or false negative reaction may be observed. If the butt of the slant is
H2S positive, and obscures the Acid-Alkaline reaction, record the butt as
acid. Always run positive and negative controls from known strains.
Procedure:
Triple sugar iron agar is used for a dual purpose. It can indicate both
carbohydrate fermentation, and hydrogen sulfide production. This test is
generally used to help identify enteric bacteria. In this procedure, bacteria
can be differentiated based on their pattern of utilization of several nutrients.
There are two parts to the test, the slant and the butt.
- Alkaline / Alkkaline - A red slant and red butt indicates the absence
of carbohydrate fermentation. - Alkaline / Acid - A yellow butt and red slant indicates glucose
fermentation only. - Acid / Acid - A yellow butt and yellow slant indicates lactose and/or
sucrose and glucose fermentation.
- H2S Positive - A black butt indicates the presence of hydrogen
sulfide production.
Tips for Success:
Examine the tubes at no earlier or later than 18-24 hours; otherwise, a false
positive or false negative reaction may be observed. If the butt of the slant is
H2S positive, and obscures the Acid-Alkaline reaction, record the butt as
acid. Always run positive and negative controls from known strains.
Procedure:
- Touch an isolated colony with a sterile needle.
- Using the needle, stab the butt, and withdraw the needle along the
same line. - Touch the same isolated colony with a sterile loop.
- Streak the surface of the slant.
- Incubate the tube for 18-24 hours.
- Observe for the presence of carbohydrate fermentation, and
hydrogen sulfide production indicated by a change in the color of the
media.
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| Triple Sugar Iron Procedure For The Identification of Bacteria |