Which is the correct interpretation of a tube of triple sugar iron TSI medium that develops a red slant and red butt?
Which is the correct interpretation of a tube of triple sugar iron TSI medium that develops a red slant and red butt?
If the medium in the butt of the tube becomes yellow (acidic), but the medium in the slant becomes red (alkaline), the organism being tested only ferments dextrose (glucose). A yellow (acidic) color in the slant and butt indicates that the organism being tested ferments dextrose, lactose and/or sucrose.
What is the purpose of the Triple sugar iron test?
Triple sugar iron agar, or TSI, is a differential medium that tests a bacterial strain for several different properties at once. It tests for acid and gas production from the fermentation of glucose and sucrose and/or lactose and for the production of hydrogen sulfide.
What is the principle of triple sugar iron TSI?
Principle. The triple sugar- iron agar test employing Triple Sugar Iron Agar is designed to differentiate among organisms based on the differences in carbohydrate fermentation patterns and hydrogen sulfide production.
Why must TSI observations be made between 18 24 hours after incubation?
This happens with Salmonella and Shigella. TSI Agar medium should be read after an incubation of only 24 hours because a longer incubation time can cause a false negative.
What test is used to differentiate between sucrose and lactose?
Wöhlk test
Since its discovery in 1904 until the 1960s, the Wöhlk test has mainly been used to detect the reducing disaccharide lactose in urine in medical laboratories.
Why is glucose added to lysine iron agar?
Lysine iron agar contains lysine, peptones, a small amount of glucose, ferric ammonium citrate, and sodium thiosulfate. When glucose is fermented, the butt of the medium becomes acidic (yellow). If the organism produces lysine decarboxylase, cadaverine is formed.
Can a mixed culture be used to inoculate TSI slant?
So the medium must be inoculated with a pure culture, often an isolated colony from another identification medium, and there will not be any useful information if it is inoculated with a mixed culture. Do not use an inoculating loop to inoculate a tube of Triple Sugar Iron Agar.
Does Pseudomonas aeruginosa ferment glucose?
P. aeruginosa has few nutritional requirements and can adapt to conditions not tolerated by other organisms. It does not ferment lactose or other carbohydrates but oxidizes glucose and xylose.
Which three things are tested for by the triple sugar iron test?
TSI agar tests organisms for 3 things: (1) carbohydrate fermentation (2) gas production, and (3) hydrogen sulfide production. Carbohydrate fermentation: TSI slants contain three carbohydrates: glucose (0.1%), sucrose (1%), and lactose (1.0%), as well as phenol red (pH indicator) and peptones.
What organism grows on triple sugar iron agar?
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.
What is the role of thiosulfate in triple sugar iron agar?
Sodium thiosulfate acts as the substrate for enzymatic reduction and the resultant colorless hydrogen sulfide gas reacts with ferrous sulfate to produce ferrous sulfide, an insoluble black precipitate.
What is the composition of triple sugar iron agar?
Triple Sugar Iron Agar. 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.
What is the composition of TSI agar?
The Triple Sugar Iron (TSI) agar is a culture medium named for its ability to test a microorganism’s ability to ferment sugars and to produce hydrogen sulfide. Composition of Triple Sugar Iron (TSI) Agar Final pH (at 25°C): 7.3 +/- 0.2 Principle of Triple Sugar Iron (TSI) Agar
What is the appearance of Pseudomonas aeruginosa on agar?
It produces Large, flat and irregularly edged circular colonies. In an ordinary medium like Nutrient Agar medium, Pseudomonas aeruginosa produces a characteristic sweetish odor or a distinctive musty or earthy smell in the medium.
What is the concentration of phenol red in TSI agar?
TSI agar slants contain a 1% concentration. The pH indicator, phenol red, is also incorporated into the medium to detect acid production from carbohydrate fermentation. to obtain approximately the same information. the agar deep with a straight inoculating needle. Incubation is for 18 to 24 hours in production, and H2S production.
