What is the color or TSI for salmonella?
Result Interpretation on Triple Sugar Iron (TSI) Agar
| Organisms | Growth |
|---|---|
| Salmonella Typhi | Red slant, yellow butt, no gas production; H2S produced |
| Salmonella Typhimurium | Red slant, yellow butt, gas production; H2S produced |
| Shigella flexneri | Red slant, yellow butt, gas negative, H2S not produced |
Is TSI selective or differential?
Triple sugar iron agar (TSI) is a differential medium that contains lactose, sucrose, a small amount of glucose (dextrose), ferrous sulfate, and the pH indicator phenol red. It is used to differentiate enterics based on the ability to reduce sulfur and ferment carbohydrates.
What is a TSI slant used for?
The Triple Sugar Iron (TSI) test is a microbiological test roughly named for its ability to test a microorganism’s ability to ferment sugars and to produce hydrogen sulfide. It is often used to differentiate enteric bacteria including Salmonella and Shigella.
How some bacteria are able to produce the black precipitate on TSI agar slant?
On the slant, the pyruvate is further metabolized to CO2, H2O, and energy. In the anerobic butt, the bacteria convert pyruvate into stable acid endproducts, thus the butt remains acidic. The black precipitate indicates that the bacteria were able to produce hydrogen sulfide (H2S) from sodium thiosulfate.
How do you read TSI results?
An alkaline/acid (red slant/yellow butt) reaction: It is indicative of dextrose fermentation only. An acid/acid (yellow slant/yellow butt) reaction: It indicates the fermentation of dextrose, lactose and/or sucrose. An alkaline/alkaline (red slant, red butt) reaction: Absence of carbohydrate fermentation results.
How do you read a TSI test?
Expected results of TSI Agar test are:
- Alkaline slant/no change in butt (K/NC) i.e Red/Red = glucose, lactose and sucrose non-fermenter.
- Alkaline slant/Alkaline butt (K/K) i.e Red/Red = glucose, lactose and sucrose non-fermenter.
How do you inoculate triple sugar iron agar?
Method
- With a straight inoculation needle, touch the top of a well-isolated colony.
- Inoculate TSI by first stabbing through the center of the medium to the bottom of the tube and then streaking the surface of the agar slant.
- Leave the cap on loosely and incubate the tube at 35°-37°C in ambient air for 18 to 24 hours.
What are the three sugars in TSI agar slants?
TSI Agar contains three sugars (dextrose, lactose and sucrose), phenol red for detecting carbohydrate fermentation, and ferrous sulfate for detection of hydrogen sulfide production (indicated by blackening in the butt of the tube).
When using triple sugar iron agar in test tube slants if the bacteria produces hydrogen sulfide what color change occurs?
black
A red (alkaline) color in the slant and butt indicates that the organism being tested is a nonfermenter. Hydrogen sulfide production results in a black precipitate in the butt of the tube. Gas production is indicated by splitting and cracking of the medium. 1.
What causes a slant to turn red or alkaline?
Due to the building of acid during fermentation, the pH falls. The meagre amount of acid production in the slant of the tube during glucose fermentation oxidizes rapidly, causing the medium to remain orange red or revert to an alkaline pH.
How is triple sugar iron agar inoculated?
Method. With a straight inoculation needle, touch the top of a well-isolated colony. Inoculate TSI by first stabbing through the center of the medium to the bottom of the tube and then streaking the surface of the agar slant. Leave the cap on loosely and incubate the tube at 35°-37°C in ambient air for 18 to 24 hours.