Biochemical tests – IMViC MCQs With Answer

Biochemical tests – IMViC MCQs With Answer

by

Biochemical tests – IMViC MCQs With Answer provide B. Pharm students a focused review of core microbiology assays used in bacterial identification. This concise guide covers the Indole, Methyl Red, Voges‑Proskauer and Citrate tests (IMViC), explaining reagents, enzymatic bases, interpretation patterns and common organism profiles. Ideal for pharmaceutical microbiology, quality control and lab practicals, these MCQs reinforce concepts like tryptophanase activity, mixed‑acid versus butanediol fermentation, Kovac’s reagent, Barritt’s reagents and Simmons’ citrate medium. Emphasis is placed on clinical and industrial relevance, troubleshooting and result significance. Practice with these targeted questions to sharpen diagnostic reasoning and exam readiness. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which enzyme is primarily responsible for a positive indole test?

  • Tryptophanase
  • Citrate permease
  • Pyruvate kinase
  • Acetoin reductase

Correct Answer: (Tryptophanase)

Q2. Kovac’s reagent is used to detect which compound in the indole test?

  • Indole
  • Acetoin
  • Glucose
  • Bromothymol blue

Correct Answer: (Indole)

Q3. A positive methyl red (MR) test indicates which metabolic pathway?

  • Mixed‑acid fermentation
  • Butanediol fermentation
  • Oxidative phosphorylation
  • Photosynthesis

Correct Answer: (Mixed‑acid fermentation)

Q4. Which pH indicator is used in the methyl red test?

  • Methyl red
  • Phenol red
  • Bromothymol blue
  • Neutral red

Correct Answer: (Methyl red)

Q5. The Voges‑Proskauer (VP) test detects the presence of which compound?

  • Acetoin (3‑hydroxybutanone)
  • Indole
  • Lactate
  • Formate

Correct Answer: (Acetoin (3‑hydroxybutanone))

Q6. Which reagents are classically used in the VP test?

  • Alpha‑naphthol and potassium hydroxide (Barritt’s reagents)
  • Kovac’s reagent and HCl
  • Methyl red and glucose
  • Bromothymol blue and citrate

Correct Answer: (Alpha‑naphthol and potassium hydroxide (Barritt’s reagents))

Q7. Simmons’ citrate agar contains which pH indicator to show citrate utilization?

  • Bromothymol blue
  • Methyl red
  • Phenolphthalein
  • Neutral red

Correct Answer: (Bromothymol blue)

Q8. A bacterium that grows on Simmons’ citrate agar and turns the medium blue is indicated to have which enzyme?

  • Citrate permease
  • Tryptophanase
  • Urease
  • Catalase

Correct Answer: (Citrate permease)

Q9. What IMViC pattern is typical for Escherichia coli?

  • Indole +, MR +, VP –, Citrate –
  • Indole –, MR –, VP +, Citrate +
  • Indole +, MR –, VP +, Citrate +
  • Indole –, MR +, VP +, Citrate –

Correct Answer: (Indole +, MR +, VP –, Citrate –)

Q10. Enterobacter aerogenes typically shows which IMViC pattern?

  • Indole –, MR –, VP +, Citrate +
  • Indole +, MR +, VP –, Citrate –
  • Indole +, MR –, VP –, Citrate +
  • Indole –, MR +, VP +, Citrate –

Correct Answer: (Indole –, MR –, VP +, Citrate +)

Q11. Why is incubation time critical for the VP test?

  • Acetoin accumulation requires sufficient incubation to be detectable
  • Kovac’s reagent degrades quickly
  • Citrate utilization only occurs after prolonged incubation
  • Methyl red indicator changes color overnight

Correct Answer: (Acetoin accumulation requires sufficient incubation to be detectable)

Q12. Which substrate is fermented leading to a positive MR result?

  • Glucose
  • Lactose
  • Sucrose
  • Fructose

Correct Answer: (Glucose)

Q13. A false‑negative indole test can result from which of the following?

  • Low tryptophan in medium or old culture
  • Using alpha‑naphthol instead of Kovac’s reagent
  • Excess citrate in the medium
  • High oxygen concentration

Correct Answer: (Low tryptophan in medium or old culture)

Q14. In MR‑VP broth, why are both tests performed from the same culture?

  • Because the medium supports both mixed‑acid and butanediol pathways
  • To save reagents by mixing tests
  • Because citrate must be present for both
  • Because tryptophanase is induced by the same medium

Correct Answer: (Because the medium supports both mixed‑acid and butanediol pathways)

Q15. Which of the following organisms is typically IMViC: + + – – ?

  • Escherichia coli
  • Enterobacter cloacae
  • Klebsiella pneumoniae
  • Serratia marcescens

Correct Answer: (Escherichia coli)

Q16. What color change indicates a positive MR test?

  • Yellow to red (red indicates positive)
  • Blue to green (green indicates positive)
  • Colorless to pink (pink indicates positive)
  • Green to yellow (yellow indicates positive)

Correct Answer: (Yellow to red (red indicates positive))

Q17. Which metabolic end product is primarily responsible for the stable low pH in MR positive organisms?

  • Mixed acids (lactate, formate, acetate)
  • Acetoin
  • Ethanol
  • Carbon dioxide only

Correct Answer: (Mixed acids (lactate, formate, acetate))

Q18. A weak VP reaction can be intensified by which procedural change?

  • Longer incubation and proper shaking after adding reagents
  • Addition of Kovac’s reagent instead of Barritt’s
  • Reducing incubation temperature to 20°C
  • Using citrate agar as a substrate

Correct Answer: (Longer incubation and proper shaking after adding reagents)

Q19. Citrate utilization leads to an alkaline shift because bacteria convert citrate to which alkaline products?

  • Ammonia and amines from ammonium salts
  • Lactic acid and acetic acid
  • Sulfuric acid and nitric acid
  • Acetoin and ethanol

Correct Answer: (Ammonia and amines from ammonium salts)

Q20. Which medium is commonly used for the indole test in a simple lab?

  • Tryptone broth
  • Simmons’ citrate agar
  • MR‑VP broth
  • MacConkey agar

Correct Answer: (Tryptone broth)

Q21. A VP positive organism would most likely produce which IMViC result?

  • MR negative, VP positive
  • MR positive, VP positive
  • MR positive, VP negative
  • MR negative, VP negative

Correct Answer: (MR negative, VP positive)

Q22. Which chemical detection principle best describes the VP test?

  • Oxidation of acetoin to diacetyl reacting with guanidine nuclei to form a red color
  • Hydrolysis of tryptophan to indole forming a red ring
  • pH change due to acid production detected by methyl red
  • Complexation of citrate with iron producing a blue complex

Correct Answer: (Oxidation of acetoin to diacetyl reacting with guanidine nuclei to form a red color)

Q23. Which IMViC test requires minimal aeration to correctly detect product formation?

  • Voges‑Proskauer requires aeration after reagent addition
  • Indole requires strict anaerobic conditions
  • Citrate requires anaerobic incubation
  • Methyl red requires shaking during incubation

Correct Answer: (Voges‑Proskauer requires aeration after reagent addition)

Q24. Which organism commonly gives IMViC: – – + + ?

  • Enterobacter aerogenes
  • Escherichia coli
  • Salmonella typhi
  • Shigella dysenteriae

Correct Answer: (Enterobacter aerogenes)

Q25. In clinical pharmaceutical testing, why are IMViC tests important?

  • They aid rapid differentiation of coliforms and enteric bacteria essential for QC
  • They sterilize contaminated samples
  • They directly quantify endotoxin levels
  • They detect viral contamination

Correct Answer: (They aid rapid differentiation of coliforms and enteric bacteria essential for QC)

Q26. A citrate negative result appears as which color on Simmons’ citrate medium?

  • Green (no change)
  • Blue (positive)
  • Red (positive)
  • Yellow (negative)

Correct Answer: (Green (no change))

Q27. Which factor can cause a false‑positive MR test?

  • Contamination with strong acidic substances or overincubation causing breakdown
  • Using Kovac’s reagent instead of methyl red
  • Incubating at 4°C
  • Using Simmons’ citrate agar

Correct Answer: (Contamination with strong acidic substances or overincubation causing breakdown)

Q28. What is the biochemical basis for the indole test?

  • Degradation of tryptophan to indole, pyruvate and ammonia by tryptophanase
  • Conversion of citrate to acetate and oxaloacetate
  • Fermentation of glucose to acetoin
  • Oxidation of sulfur compounds

Correct Answer: (Degradation of tryptophan to indole, pyruvate and ammonia by tryptophanase)

Q29. Which quality control organism is commonly used as a positive control for indole?

  • Escherichia coli (indole positive)
  • Enterobacter cloacae (indole negative)
  • Klebsiella pneumoniae (indole negative)
  • Pseudomonas aeruginosa (indole negative)

Correct Answer: (Escherichia coli (indole positive))

Q30. What does a delayed positive VP test indicate about bacterial metabolism?

  • Slow butanediol pathway with gradual accumulation of acetoin
  • Immediate mixed‑acid fermentation
  • Absence of tryptophanase
  • Inability to utilize citrate

Correct Answer: (Slow butanediol pathway with gradual accumulation of acetoin)

Q31. Which component in Simmons’ citrate agar is the sole carbon source?

  • Sodium citrate
  • Glucose
  • Lactose
  • Peptone

Correct Answer: (Sodium citrate)

Q32. If MR and VP are both negative, what can be inferred about glucose metabolism?

  • The organism does not produce stable mixed acids or acetoin in detectable amounts
  • The organism is a strict anaerobe
  • The organism degrades tryptophan extensively
  • The organism uses citrate as sole carbon source

Correct Answer: (The organism does not produce stable mixed acids or acetoin in detectable amounts)

Q33. Which reagent would you add to detect indole in a tube culture?

  • Kovac’s reagent (p‑dimethylaminobenzaldehyde in amyl alcohol)
  • Methyl red
  • Alpha‑naphthol and KOH
  • Bromothymol blue

Correct Answer: (Kovac’s reagent (p‑dimethylaminobenzaldehyde in amyl alcohol))

Q34. The presence of which gene product is necessary for citrate utilization?

  • Citrate permease (cit operon related proteins)
  • Tryptophan synthase
  • Lactate dehydrogenase
  • Beta‑galactosidase

Correct Answer: (Citrate permease (cit operon related proteins))

Q35. Which IMViC profile is typical for Klebsiella pneumoniae?

  • Indole –, MR –, VP +, Citrate +
  • Indole +, MR +, VP –, Citrate –
  • Indole –, MR +, VP –, Citrate –
  • Indole +, MR –, VP +, Citrate –

Correct Answer: (Indole –, MR –, VP +, Citrate +)

Q36. Excess peptone in Simmons’ citrate medium can cause which issue?

  • False negative due to alternative carbon sources supporting growth without citrate utilization
  • Immediate blue color without growth
  • False positive indole reaction
  • Inhibition of VP reagents

Correct Answer: (False negative due to alternative carbon sources supporting growth without citrate utilization)

Q37. Which step is critical when performing the VP test after adding reagents?

  • Vigorous shaking to aerate the mixture and allow oxidation
  • Incubation in anaerobic jar
  • Immediate refrigeration
  • Adding Kovac’s reagent instead of Barritt’s

Correct Answer: (Vigorous shaking to aerate the mixture and allow oxidation)

Q38. What is the role of peptone in Simmons’ citrate agar?

  • Provides nitrogen source (ammonium) for deamination producing alkalinity
  • Serves as the sole carbon source
  • Acts as the pH indicator
  • Neutralizes the medium to prevent growth

Correct Answer: (Provides nitrogen source (ammonium) for deamination producing alkalinity)

Q39. Which statement about IMViC tests is correct for environmental isolates?

  • IMViC patterns help infer metabolic capabilities but require confirmation with additional tests
  • IMViC alone can fully identify species in environmental samples
  • Indole is used to test for spore formation
  • Citrate utilization always predicts pathogenicity

Correct Answer: (IMViC patterns help infer metabolic capabilities but require confirmation with additional tests)

Q40. During MR testing, why must you read results promptly after adding methyl red?

  • The indicator can change color over time and give false readings
  • Methyl red evaporates rapidly
  • Bacteria die instantly upon contact
  • The medium solidifies

Correct Answer: (The indicator can change color over time and give false readings)

Q41. Which metabolic trait leads to VP positivity instead of MR positivity?

  • Butanediol fermentation pathway producing neutral end products like acetoin
  • Complete oxidation of glucose to CO2 only
  • High production of indole
  • Use of citrate as sole carbon source

Correct Answer: (Butanediol fermentation pathway producing neutral end products like acetoin)

Q42. When interpreting IMViC results, why is colony morphology and Gram reaction also important?

  • They provide additional context to differentiate species with similar IMViC patterns
  • They determine VP reagent choice
  • They negate the need for biochemical tests
  • They change the color of methyl red

Correct Answer: (They provide additional context to differentiate species with similar IMViC patterns)

Q43. Which IMViC combination is most likely for Proteus species?

  • Indole variable, MR +, VP – , Citrate variable (depends on species)
  • Indole –, MR –, VP +, Citrate +
  • Indole +, MR –, VP +, Citrate +
  • Indole –, MR +, VP +, Citrate –

Correct Answer: (Indole variable, MR +, VP – , Citrate variable (depends on species))

Q44. What precaution should be taken when storing Simmons’ citrate plates?

  • Avoid excessive moisture and prolonged storage that can alter indicator and nutrient availability
  • Always keep plates frozen
  • Light exposure will sterilize the plates
  • Store submerged in saline

Correct Answer: (Avoid excessive moisture and prolonged storage that can alter indicator and nutrient availability)

Q45. In an MR‑VP broth tube, appearance of a pink/red color after methyl red addition indicates what pH range?

  • pH ≤ 4.4 (acidic)
  • pH 6.0–7.0 (neutral)
  • pH ≥ 6.0 (alkaline)
  • pH 8.5–9.5 (strongly alkaline)

Correct Answer: (pH ≤ 4.4 (acidic))

Q46. Which test in IMViC series is most useful to distinguish between Escherichia and Enterobacter genera?

  • Indole and citrate reactions are particularly distinguishing
  • Urease test only
  • Nitrate reduction only
  • Oxidase test only

Correct Answer: (Indole and citrate reactions are particularly distinguishing)

Q47. A lab student observes a brown ring instead of red in indole test. What might this indicate?

  • Oxidation of indole reagent or contamination; test should be repeated
  • Strong positive indole
  • Positive VP reaction interfering
  • Normal citrate utilization

Correct Answer: (Oxidation of indole reagent or contamination; test should be repeated)

Q48. Which IMViC test result is most influenced by medium composition and incubation conditions?

  • All tests can be influenced, but VP and citrate are particularly sensitive to conditions
  • Only indole is sensitive
  • MR is never affected by medium
  • None of the tests are influenced by conditions

Correct Answer: (All tests can be influenced, but VP and citrate are particularly sensitive to conditions)

Q49. In pharmaceutical QC, if an unknown coliform shows IMViC pattern + – – –, what is the most likely interpretation?

  • Indole positive but does not perform mixed‑acid fermentation, acetoin production or citrate utilization; species identification required
  • Typical Enterobacter profile
  • Typical Klebsiella profile
  • Non‑enteric environmental organism

Correct Answer: (Indole positive but does not perform mixed‑acid fermentation, acetoin production or citrate utilization; species identification required)

Q50. For accurate IMViC interpretation, which of the following best practices should be followed?

  • Use fresh cultures, correct media, proper incubation times and include positive/negative controls
  • Use only old cultures and high temperatures
  • Add all reagents simultaneously at start of incubation
  • Interpret results weeks after incubation without controls

Correct Answer: (Use fresh cultures, correct media, proper incubation times and include positive/negative controls)

Leave a Comment