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Questions and Answers
What is the purpose of the triple sugar iron test?
What is the purpose of the triple sugar iron test?
The TSI test is designed to differentiate among the different groups or genera of the Enterobacteriaceae, which are all gram-negative bacilli capable of fermenting glucose with the production of acid, and to distinguish the Enterobacteriaceae from other gram-negative intestinal bacilli.
What are the Enterobacteriaceae?
What are the Enterobacteriaceae?
All gram-negative bacilli capable of fermenting glucose with the production of acid.
What is the differentiation based on in the TSI test?
What is the differentiation based on in the TSI test?
The differentiation is made on the basis of the differences in carbohydrate fermentation patterns and hydrogen sulfide production.
What kind of tool does the TSI test use?
What kind of tool does the TSI test use?
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What happens if only glucose is fermented?
What happens if only glucose is fermented?
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What happens if either lactose or sucrose are fermented?
What happens if either lactose or sucrose are fermented?
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How are TSI slants inoculated?
How are TSI slants inoculated?
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What are the reactions observed after inoculating the TSI slants for 24-48 hours?
What are the reactions observed after inoculating the TSI slants for 24-48 hours?
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What type of bacteria would you use the TSI test for?
What type of bacteria would you use the TSI test for?
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How would you identify an acidic slant?
How would you identify an acidic slant?
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Why is there more lactose and sucrose in TSI agar than glucose?
Why is there more lactose and sucrose in TSI agar than glucose?
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What does a red slant and red butt indicate?
What does a red slant and red butt indicate?
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What does a red slant and yellow butt indicate?
What does a red slant and yellow butt indicate?
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What does a yellow slant and yellow butt indicate?
What does a yellow slant and yellow butt indicate?
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What does cracks or lifting in the agar signify?
What does cracks or lifting in the agar signify?
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What does blackening of agar represent?
What does blackening of agar represent?
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Study Notes
Purpose of the TSI Test
- Differentiates among various groups of Enterobacteriaceae, all of which are gram-negative bacilli capable of fermenting glucose and producing acid.
- Helps distinguish Enterobacteriaceae from other gram-negative intestinal bacilli.
Enterobacteriaceae Overview
- Comprises all gram-negative bacilli with the ability to ferment glucose, leading to acid production.
Basis of Differentiation
- Differentiation relies on carbohydrate fermentation patterns and hydrogen sulfide production.
Test Components
- Utilizes an agar slant containing lactose (1%), sucrose (1%), and a low concentration of glucose (0.1%).
- Incorporates a pH indicator (phenol red) to detect acid produced during fermentation.
Glucose Fermentation Results
- Fermentation of only glucose results in a yellow butt (bottom) and red slant due to limited acid production from the low glucose concentration.
Lactose/Sucrose Fermentation Results
- Fermentation of lactose or sucrose produces a yellow butt and yellow slant, indicating extensive acid production due to their higher concentrations.
Inoculation Technique
- Inoculated using an inoculating needle: stab the butt to a depth of 0.5 cm and streak the surface in a zig-zag motion.
Observations Post-Inoculation (24-48 hours)
- Yellow butt and red slant indicate fermentation of ONLY glucose.
- Yellow butt and yellow slant indicate fermentation of lactose and/or sucrose.
- Gas formation is identified by cracks or lifting in the agar.
- Hydrogen sulfide production is indicated by blackening of the agar.
- Red butt and red slant signal no fermentation or gas/hydrogen sulfide production.
Suitable Bacteria for TSI Test
- Primarily used for testing Enterobacteriaceae.
Acidic Slant Identification
- An acidic slant will turn yellow.
Sugar Concentration Rationale
- Higher concentrations of lactose and sucrose in TSI agar allow differentiation between bacteria that only ferment glucose and those that can ferment lactose/sucrose.
Fermentation Results Interpretation
- Red slant/red butt indicates no fermentation.
- Red slant/yellow butt signifies glucose fermentation.
- Yellow slant/yellow butt indicates fermentation of lactose and/or sucrose.
- Cracks or lifting in the agar denote gas production.
- Blackening of agar reveals hydrogen sulfide production.
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Description
This quiz covers the objectives and components of the TSI test used for differentiating Enterobacteriaceae. It highlights how glucose, lactose, and sucrose fermentation patterns are evaluated to distinguish these gram-negative bacilli. Test your knowledge on the principles behind the TSI test and its significance in microbiological diagnostics.