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14 Cards in this Set
- Front
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Introduction |
The Triple sugar Iron (TSI) test is a microbiological test roughly named for its ability to test microorganism's ability to ferment sugars and to produce hydrogen sulfide.
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Intended Use
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Triple sugar Iron medium is a differential medium that can distinguish between a number of Gram-negative enteric bacteria based on their physiological ability (or lack thereof) to:
a. metabolize lactose and/or sucrose b. conduct fermentation to produce acid c. produce gas during fermentation. d. generate H2S. |
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History
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- In 1911, Russell described the use of an agar medium with two sugars to aid in the identification of intestinal gram-negative bacilli
- Kliger added lead acetate and iron salts to detect hydrogen sulfide production and used phenol red as a pH indicator producing Kigler’s Iron Agar. -In 1940, Difco Laboratories, Sulkin and Willet, and Hajna described a similar to triple sugar ferrous sulfate medium for the identification of enteric bacilli. |
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Composition |
Contains three carbohydrates: glucose (0.1%), sucrose (1%), and lactose (1%) as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate.
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Why slant used |
The slanted shape of this medium provides an array of surfaces that are either exposed to oxygen-containing air in varying degrees (an aerobic environment) .
The slant of the medium is aerobic, while the deep (or butt) is anaerobic. |
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Principle
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The differentiation is based on the differences in carbohydrate fermentation patterns and hydrogen sulfide production by the various groups of intestinal organisms.
-Carbohydrate fermentation is indicated by the presence of gas and a visible color change of the pH indicator, phenol red. -The production of hydrogen sulphide in the medium is indicated by the formation of a black precipitate that will blacken the medium in the butt of the tube |
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Function of ingredients used in media: a) phenol red. |
pH indicator : below 6.8 it is yellow above 82., it is red
Failure to turn the butt yellow indicates that no fermentation has occurred, and that the bacterium is an obligate aerobe |
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b) glucose |
If only glucose is fermented, only a small amount of acid is produced to turn the butt yellow. The slant will remain red.
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c) lactose and sucrose |
If the culture can ferment either lactose (lac+) and/or sucrose (suc+), a large amount of acid is produced
-A large amount of acid turns both butt and slant yellow, thus indicating the ability of the culture to ferment either lactose or sucrose |
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d) FeSO4 (ferrous sulfate) |
A source of iron and sulfur.
A few bacteria are capable of reducing the SO4= to H2S (hydrogen sulfide). The iron combines with the H2S to form FeS (ferrous sulfide) a black compound. This will turn the butt black. Thus, a black butt indicates H2S production. |
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Result -SLANT |
- RED Slant - does not ferment either lactose or sucrose - YELLOW - ferments lactose and/or sucrose |
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Result |
- RED - fermentation, the bacterium is an obligate aerobe -YELLOW - some fermentation has occurred, acid has been produced, it is a facultative anaerobe. -GAS FORMED - Seen as cracks in the agar, bubbles, or the entire slant may be pushed out of the tube. -BLACK - H2S has been produced |
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Interpretation
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Bacteria that ferment any of the three sugars in the medium will produce byproducts ( acids )
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For more Information |
https://www.blogger.com/blogger.g?blogID=5065214763789161932#allposts
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