Triple Sugar Iron (TSI) Agar Mock Test: 30 Practice MCQs for Lab Professionals & Students

Triple Sugar Iron (TSI) Agar is a cornerstone of biochemical testing in clinical microbiology. This differential medium identifies Gram-negative enteric bacteria based on carbohydrate fermentation (glucose, lactose, sucrose) and hydrogen sulfide production. For lab professionals and students, interpreting TSI slants—decoding color changes, gas formation, and H₂S production—is essential for accurate pathogen identification.

Who Should Take This Mock Test?

Medical laboratory science students
Microbiology certification aspirants
Lab technicians preparing for competency exams
Professionals refreshing their bacteriology skills

Test Features:
✅ 30 expertly crafted MCQs covering TSI principles, reactions, and organism identification
✅ Real-world scenarios mimicking clinical lab challenges
✅ Aligned with ASCP, AMT, and global certification standards

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Pro Tip: Review these concepts before starting:

Slant/butt color interpretations (alkaline/acidic shifts)
H₂S production mechanisms (black precipitate)
Common reactions of Salmonella, Shigella, E. coli, and Proteus

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Microbiology Department

Triple Sugar Iron (TSI) Agar MCQs Mock Test

🔥 Free 30 MCQs on Triple Sugar Iron (TSI) Agar! Master slant reactions, H₂S production & pathogen identification with this mock test. Perfect for medical lab students, technologists, and certification prep. Test your skills now!

💡 Level Up Your TSI Agar Interpretation! Ace your lab exams with 30 targeted MCQs on Triple Sugar Iron Agar reactions. Designed for MLT students & professionals. Free mock test → Benchmark your skills!

Read Full Article: Triple Sugar Iron (TSI) Agar FAQs and MCQs

1 / 30

Category: Clinical Laboratory

What is the expected TSI result for Shigella flexneri?

Red slant/red butt

Yellow slant/yellow butt, gas, no H₂S

Red slant/yellow butt, no gas, no H₂S

Yellow slant/black butt

2 / 30

Category: Clinical Laboratory

What does a completely black TSI tube indicate?

Only H₂S production

Contamination

No bacterial growth

Over-fermentation of all sugars

3 / 30

Category: Clinical Laboratory

What causes false-positive gas production in TSI?

Incubating for less than 18 hours

Using expired agar

Using a loop instead of a needle

Tightening the tube cap

4 / 30

Category: Clinical Laboratory

What is a limitation of TSI Agar?

It may give false negatives if read after 24 hours

It cannot detect H₂S

It only works for gram-positive bacteria

It requires anaerobic incubation

5 / 30

Category: Clinical Laboratory

Which medium is more sensitive for H₂S detection than TSI?

SIM Medium

Mannitol Salt Agar

Blood Agar

MacConkey Agar

6 / 30

Category: Clinical Laboratory

Which sugar is optional for differentiating Salmonella and Shigella in TSI?

Maltose

Glucose

Lactose

Sucrose

7 / 30

Category: Clinical Laboratory

Why is a pure culture essential for TSI testing?

It increases H₂S production

Contaminants degrade the agar

Mixed cultures can give false results

Only gram-negatives grow

8 / 30

Category: Clinical Laboratory

What is the final pH of TSI Agar before inoculation?

7.3 ± 0.2

6.0 ± 0.2

8.0 ± 0.2

5.4 ± 0.2

9 / 30

Category: Clinical Laboratory

Which organism shows a red slant, yellow butt, and H₂S production?

Klebsiella pneumoniae

Pseudomonas aeruginosa

Escherichia coli

Salmonella Typhi

10 / 30

Category: Clinical Laboratory

If a TSI tube shows a red slant, yellow butt, and black precipitate, which organism is likely?

E. coli

Enterobacter aerogenes

Shigella sonnei

Salmonella Typhimurium

11 / 30

Category: Clinical Laboratory

What happens if TSI is incubated beyond 24 hours?

Acid in the slant may revert to alkaline

H₂S disappears

The slant turns blue

Gas production stops

12 / 30

Category: Clinical Laboratory

What does a red slant and yellow butt indicate?

H₂S production

Glucose fermentation only

No fermentation

Lactose/sucrose fermentation

13 / 30

Category: Clinical Laboratory

Why must the tube cap be loosened during incubation?

To reduce evaporation

To prevent contamination

To enhance H₂S production

To allow oxygen exchange for slant alkalinity

14 / 30

Category: Clinical Laboratory

What is the TSI reaction of E. coli?

Red slant/yellow butt

Red slant/red butt

Yellow slant/black butt

Yellow slant/yellow butt with gas

15 / 30

Category: Clinical Laboratory

Which organism shows an alkaline/alkaline (red/red) reaction?

Proteus vulgaris

Pseudomonas aeruginosa

Citrobacter freundii

Shigella flexneri

16 / 30

Category: Clinical Laboratory

What does a black precipitate in the butt indicate?

Gas production

H₂S production

Lactose fermentation

Glucose fermentation

17 / 30

Category: Clinical Laboratory

Which test should follow TSI for definitive identification?

IMViC tests

Gram staining

Catalase test

Coagulase test

18 / 30

Category: Clinical Laboratory

Why is the glucose concentration lower than lactose and sucrose in TSI?

To enhance H₂S production

To prevent over-acidification

To detect weak glucose fermenters

To reduce cost

19 / 30

Category: Clinical Laboratory

Which pH indicator is used in TSI Agar?

Methyl red

Bromothymol blue

Neutral red

Phenol red

20 / 30

Category: Clinical Laboratory

Which of the following is H₂S-positive on TSI?

Enterobacter aerogenes

Klebsiella pneumoniae

Shigella sonnei

Proteus mirabilis

21 / 30

Category: Clinical Laboratory

Why might sucrose suppress H₂S production in some bacteria?

It increases pH

It competes with thiosulfate

It alters enzymatic pathways

It inhibits iron salts

22 / 30

Category: Clinical Laboratory

A TSI tube has a yellow slant, yellow butt, and gas but no H₂S. Which organism fits?

Klebsiella pneumoniae

Salmonella Typhi

Citrobacter freundii

Proteus vulgaris

23 / 30

Category: Clinical Laboratory

Which organism may show delayed H₂S production on TSI?

E. coli

Salmonella Paratyphi A

Klebsiella pneumoniae

Pseudomonas aeruginosa

24 / 30

Category: Clinical Laboratory

What is the concentration of glucose in TSI Agar?

10%

0.1%

25 / 30

Category: Clinical Laboratory

How should TSI Agar be inoculated?

Only stab the butt

Spread on the surface

Stab the butt and streak the slant

Only streak the slant

26 / 30

Category: Clinical Laboratory

How is gas production detected in TSI Agar?

Bubbles or cracks in the agar

Black precipitate

Cloudiness in the medium

Change to blue color

27 / 30

Category: Clinical Laboratory

What is the purpose of ferrous ammonium sulfate in TSI Agar?

To detect gas production

To inhibit gram-positive bacteria

To detect lactose fermentation

To detect H₂S production

28 / 30

Category: Clinical Laboratory

What does a yellow slant and yellow butt indicate?

H₂S production only

No fermentation

Glucose fermentation only

Lactose/sucrose fermentation

29 / 30

Category: Clinical Laboratory

What is the primary use of TSI Agar?

To differentiate Enterobacteriaceae

To test antibiotic resistance

To identify gram-positive cocci

To detect spore-forming bacteria

30 / 30

Category: Clinical Laboratory

Why is TSI not used for gram-positive bacteria?

They do not ferment sugars

They do not produce H₂S

They are inhibited by the medium

The pH indicator doesn’t work

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How to Maximize Your Results

Analyze Weak Areas: Missed questions on H₂S production? Revisit bacterial metabolism pathways.
Deepen Understanding: Confused about alkaline slant/acidic butt? Study glucose fermentation limitations.
Use Visual Aids: Download our free TSI Agar Reaction Chart (link) for quick reference.

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