Triple sugar iron agar showing gas production with red slant and yellow butt. The organism cultured is –
## Core Concept
The question assesses understanding of the Triple Sugar Iron (TSI) agar test, a tool used in microbiology to differentiate bacteria based on their ability to ferment sugars and produce gas. TSI agar contains three sugars: glucose, lactose, and sucrose, along with an indicator to track pH changes. The test is crucial for identifying enteric bacteria.
## Why the Correct Answer is Right
The description provided - gas production with a red slant and yellow butt on TSI agar - is characteristic of a specific pattern of sugar fermentation. The red slant indicates that the organism does not ferment lactose or sucrose, as these fermentations would acidify the medium (turning it yellow). The yellow butt indicates fermentation of glucose, which produces acid and turns the butt yellow. Gas production is evident from the cracks or bubbles in the agar. This pattern is typical for *Salmonella* species, which ferment glucose but not lactose or sucrose.
## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not match the described TSI reaction. Without specifics on the organism, we can't detail why, but it doesn't fit the given reaction.
- **Option B:** Similarly, this option does not align with the provided TSI agar results. The correct organism should produce gas, have a red slant (indicating no lactose/sucrose fermentation), and a yellow butt (indicating glucose fermentation).
- **Option C:** This is the correct answer, as explained.
- **Option D:** This option is incorrect because it presumably does not match the TSI agar results described. The details of why aren't provided, but it doesn't fit the pattern of gas production with a red slant and yellow butt.
## Clinical Pearl / High-Yield Fact
A key point to remember is that *Salmonella* species are known for their ability to produce gas and for having a TSI agar reaction that typically shows a red slant (no lactose/sucrose fermentation) and a yellow butt (glucose fermentation). This characteristic pattern helps in the identification of these pathogens in the clinical laboratory.
## Correct Answer: C. Salmonella.