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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.



Intended Use
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.

History
- 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.



Composition

Contains three carbohydrates: glucose (0.1%), sucrose (1%), and lactose (1%) as well as sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate.

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.

Principle
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

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

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.

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

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.

Result


-SLANT

- RED Slant - does not ferment either lactose or sucrose




- YELLOW - ferments lactose and/or sucrose





Result

- BUTT

- 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

Interpretation




Bacteria that ferment any of the three sugars in the medium will produce byproducts ( acids )

For more Information

https://www.blogger.com/blogger.g?blogID=5065214763789161932#allposts
https://www.blogger.com/blogger.g?blogID=5065214763789161932#allposts