Cultivation of anaerobes MCQs With Answer

Cultivation of anaerobes MCQs With Answer

The cultivation of anaerobes is a core topic for B.Pharm students studying microbiology and clinical pharmacy. This introduction covers anaerobic culture principles, anaerobic media, oxygen-reduction techniques, anaerobic chambers, GasPak systems, roll-tube and Hungate methods, redox potential management, and sample collection/transport for oxygen-sensitive bacteria. Understanding selective agents, indicators such as resazurin and methylene blue, incubation conditions, and identification tools (biochemical tests, MALDI-TOF, molecular assays) prepares students for lab practice and pharmacy-related infection control. Emphasis is placed on practical troubleshooting, spore-formers, facultative vs obligate anaerobes, and antibiotic susceptibility testing under anaerobic conditions. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. What is the primary purpose of using reducing agents in anaerobic culture media?

To supply extra nutrients for anaerobes
To lower the redox potential and remove dissolved oxygen
To increase osmotic pressure for selective growth
To inhibit spore formation

Correct Answer: To lower the redox potential and remove dissolved oxygen

Q2. Which indicator is commonly used to detect the presence of oxygen in anaerobic media?

Phenol red
Resazurin
Crystal violet
Bromothymol blue

Correct Answer: Resazurin

Q3. The Hungate technique is primarily used for which purpose?

Quantifying obligate aerobes
Isolating and cultivating strict anaerobes in tubes under oxygen-free gas
Measuring antibiotic susceptibility aerobically
Staining anaerobes for microscopy

Correct Answer: Isolating and cultivating strict anaerobes in tubes under oxygen-free gas

Q4. Which gas mixture is most suitable for creating an anaerobic atmosphere in an anaerobic chamber?

Air (21% O2, 78% N2)
100% Carbon dioxide
85% Nitrogen, 10% Hydrogen, 5% Carbon dioxide
100% Oxygen

Correct Answer: 85% Nitrogen, 10% Hydrogen, 5% Carbon dioxide

Q5. What role does palladium catalyst play in GasPak jars?

Absorbs carbon dioxide
Converts hydrogen and residual oxygen to water, removing oxygen
Generates hydrogen gas
Acts as a nutrient for anaerobes

Correct Answer: Converts hydrogen and residual oxygen to water, removing oxygen

Q6. Which medium is commonly used for primary isolation of Bacteroides fragilis?

MacConkey agar
Bacteroides Bile Esculin (BBE) agar
Mannitol salt agar
Chocolate agar

Correct Answer: Bacteroides Bile Esculin (BBE) agar

Q7. Which characteristic differentiates obligate anaerobes from facultative anaerobes?

Obligate anaerobes can use oxygen as terminal electron acceptor
Obligate anaerobes are killed or inhibited by oxygen
Facultative anaerobes cannot grow in absence of oxygen
Facultative anaerobes form spores

Correct Answer: Obligate anaerobes are killed or inhibited by oxygen

Q8. What is the significance of redox potential (Eh) in anaerobic cultivation?

Higher Eh favors strict anaerobes
Lower Eh (more negative) is required for growth of strict anaerobes
Eh only affects aerobes, not anaerobes
Eh determines pH of the medium

Correct Answer: Lower Eh (more negative) is required for growth of strict anaerobes

Q9. Which of the following is a common selective agent used to suppress aerobes in anaerobic culture media?

Penicillin
Kanamycin and vancomycin combination
Crystal violet alone
High salt concentration

Correct Answer: Kanamycin and vancomycin combination

Q10. Why is transport medium required for clinical specimens suspected of containing anaerobes?

To promote aerobic overgrowth
To maintain anaerobic environment and viability during transport
To sterilize the sample
To increase oxygen exposure for enrichment

Correct Answer: To maintain anaerobic environment and viability during transport

Q11. Which one of these tests helps differentiate Clostridium perfringens from other Clostridium species on egg yolk agar?

Indole production
Lecithinase (opaque zone) activity
Oxidase positivity
Mannitol fermentation

Correct Answer: Lecithinase (opaque zone) activity

Q12. What does a positive esculin hydrolysis (blackening) on BBE agar indicate?

Presence of Clostridium difficile
Ability to hydrolyze esculin; characteristic of Bacteroides fragilis group
Presence of aerobic gram-negative bacilli
Production of hydrogen sulfide only

Correct Answer: Ability to hydrolyze esculin; characteristic of Bacteroides fragilis group

Q13. Which staining pitfall is common when examining anaerobic bacteria collected from clinical specimens?

Anaerobes never stain with Gram stain
Exposure to oxygen during smear preparation can alter morphology and Gram reaction
Anaerobes always appear as long filamentous forms
Heat fixation must be avoided for anaerobes

Correct Answer: Exposure to oxygen during smear preparation can alter morphology and Gram reaction

Q14. Which anaerobe is most commonly associated with gas gangrene and produces alpha toxin?

Bacteroides fragilis
Clostridium perfringens
Peptostreptococcus anaerobius
Prevotella melaninogenica

Correct Answer: Clostridium perfringens

Q15. When performing anaerobic culture in tubes, why is media often boiled and cooled under oxygen-free gas before inoculation?

To sterilize the medium repeatedly
To drive off dissolved oxygen and allow reduction under anaerobic gas
To concentrate nutrients
To denature proteins for selective growth

Correct Answer: To drive off dissolved oxygen and allow reduction under anaerobic gas

Q16. Which biochemical test is classically positive in some Bacteroides species and used for identification?

Catalase positive
Bile-esculin hydrolysis
Oxidase positive
Urease positive

Correct Answer: Bile-esculin hydrolysis

Q17. What is the advantage of using an anaerobic workstation (glove box) over a jar system?

Workstations are less expensive
They provide continuous oxygen-free working environment and better control of atmosphere
They require no maintenance
They are portable for field work

Correct Answer: They provide continuous oxygen-free working environment and better control of atmosphere

Q18. In anaerobic susceptibility testing, why must plates be incubated anaerobically during both inoculation and incubation?

To improve aerobic growth for comparison
Because oxygen exposure can inactivate antibiotics
To ensure anaerobes grow in conditions matching testing environment and maintain reproducibility
Because antibiotics require reducing conditions to work

Correct Answer: To ensure anaerobes grow in conditions matching testing environment and maintain reproducibility

Q19. Which of these bacteria is an obligate anaerobe commonly found in the oral cavity and associated with dental infections?

Neisseria gonorrhoeae
Peptostreptococcus spp.
Streptococcus pyogenes
Pseudomonas aeruginosa

Correct Answer: Peptostreptococcus spp.

Q20. What is the purpose of using thioglycollate broth in anaerobic microbiology?

To select for Gram-negative aerobes
To support growth across oxygen gradients and as an enrichment medium for anaerobes
To detect urease producers
To act as a transport medium only

Correct Answer: To support growth across oxygen gradients and as an enrichment medium for anaerobes

Q21. Which conservation method is most reliable for long-term preservation of strict anaerobes?

Repeated subculturing under aerobic conditions
Freeze-drying (lyophilization) or deep freezing under anaerobic conditions
Storage in plain nutrient broth at room temperature
Drying on filter paper in air

Correct Answer: Freeze-drying (lyophilization) or deep freezing under anaerobic conditions

Q22. Which of the following is true about Clostridium difficile diagnosis in the lab?

C. difficile is identified primarily by lactose fermentation
Toxin detection (A/B) or PCR are standard diagnostic methods, often combined with selective anaerobic culture
C. difficile grows well on MacConkey agar aerobically
Gram stain alone suffices for diagnosis

Correct Answer: Toxin detection (A/B) or PCR are standard diagnostic methods, often combined with selective anaerobic culture

Q23. Which anaerobic culture method uses agar tubes rolled to form a thin layer for colony isolation?

Pour plate method
Roll-tube (or roll-plate) method
Spread plate on open plates
Broth dilution

Correct Answer: Roll-tube (or roll-plate) method

Q24. Which metabolic capability is often used to identify certain Clostridium species?

Nitrate reduction to nitrogen gas
Spore formation and toxin production such as lecithinase
Oxidase positivity
Capsule production visualized by India ink

Correct Answer: Spore formation and toxin production such as lecithinase

Q25. What effect does oxygen have on enzymes like superoxide dismutase and catalase in strict anaerobes?

Strict anaerobes usually have abundant catalase
Many strict anaerobes lack protective enzymes and are damaged by reactive oxygen species
Oxygen activates their growth via these enzymes
These enzymes convert oxygen into nutrient sources

Correct Answer: Many strict anaerobes lack protective enzymes and are damaged by reactive oxygen species

Q26. Which agar is useful for isolation and presumptive identification of Prevotella and Porphyromonas by pigment production?

Blood agar incubated anaerobically
Torula yeast agar
MacConkey agar
Cetrimide agar

Correct Answer: Blood agar incubated anaerobically

Q27. In an anaerobic jar using GasPak sachets, what gas is typically produced by the sachet chemicals?

Oxygen
Hydrogen and carbon dioxide
Nitrogen and methane
Helium

Correct Answer: Hydrogen and carbon dioxide

Q28. Which of the following methods provides rapid identification of anaerobic isolates in modern labs?

MALDI-TOF mass spectrometry
Traditional biochemical tests only
Observation of colony color alone
Microscopic motility only

Correct Answer: MALDI-TOF mass spectrometry

Q29. Which factor is most critical when collecting pus from an abscess for anaerobic culture?

Expose the sample to air for 30 minutes before transport
Collect using aerobic swabs only
Avoid contamination with skin flora and transfer to anaerobic transport medium promptly
Heat the sample to reduce contamination

Correct Answer: Avoid contamination with skin flora and transfer to anaerobic transport medium promptly

Q30. Which species is known for producing black-pigmented colonies and is implicated in periodontal disease?

Bacteroides fragilis
Porphyromonas gingivalis
Clostridium botulinum
Escherichia coli

Correct Answer: Porphyromonas gingivalis

Q31. What is the typical incubation temperature for most clinically relevant anaerobes?

4°C
25°C
35–37°C
60°C

Correct Answer: 35–37°C

Q32. Which of these is a reliable method to confirm anaerobiosis inside a jar or chamber?

Measuring CO2 alone
Using anaerobic indicator strips (resazurin or methylene blue) and biological indicators such as control organisms
Relying on the jar lid color
Counting colony forming units immediately

Correct Answer: Using anaerobic indicator strips (resazurin or methylene blue) and biological indicators such as control organisms

Q33. Which antibiotic is commonly used to select for anaerobes when added to culture media to inhibit aerobes?

Amphotericin B
Kanamycin
Streptomycin solely
Penicillin alone

Correct Answer: Kanamycin

Q34. In the lab, which morphological feature suggests a Clostridium species on direct smear?

Gram-negative rods with polar flagella
Gram-positive rods that may be swollen with subterminal or terminal spores
Gram-positive cocci in clusters
Spiral-shaped gram-negative rods

Correct Answer: Gram-positive rods that may be swollen with subterminal or terminal spores

Q35. Which cultural trait helps distinguish Bacteroides from Prevotella and Porphyromonas?

Bacteroides are obligate aerobes
Bacteroides grow on BBE agar and often bile-resistant
Prevotella grow on MacConkey agar
Porphyromonas are catalase positive

Correct Answer: Bacteroides grow on BBE agar and often bile-resistant

Q36. What is the clinical importance of identifying anaerobic bacteria from mixed infections?

Anaerobes are always contaminants and irrelevant
They can influence disease severity, abscess formation, and antibiotic choice due to specific resistance patterns
Anaerobes only affect lab results, not therapy
They reduce virulence of aerobes

Correct Answer: They can influence disease severity, abscess formation, and antibiotic choice due to specific resistance patterns

Q37. Which test is useful for detection of Clostridium difficile toxin production in stool?

Coagulase test
Enzyme immunoassay (EIA) for toxins or PCR for toxin genes
Oxidase test
Gram stain only

Correct Answer: Enzyme immunoassay (EIA) for toxins or PCR for toxin genes

Q38. Why is pre-reduction of media important before inoculating strict anaerobes?

To increase agar hardness
To ensure the medium has a low redox potential and minimal dissolved oxygen supporting anaerobe viability
To sterilize the surface
To add antibiotics evenly

Correct Answer: To ensure the medium has a low redox potential and minimal dissolved oxygen supporting anaerobe viability

Q39. Which molecular method can rapidly identify anaerobic species directly from culture or clinical material?

16S rRNA gene sequencing or species-specific PCR
Gram staining
Enterotube testing
Collagenase assay

Correct Answer: 16S rRNA gene sequencing or species-specific PCR

Q40. What is a common reason anaerobes fail to grow from clinical specimens?

Specimens are collected and transported anaerobically
Inappropriate sample type, oxygen exposure, prior antibiotics, or delayed processing
Using selective anaerobic media
Incubation at 37°C

Correct Answer: Inappropriate sample type, oxygen exposure, prior antibiotics, or delayed processing

Q41. Which metabolic product is often produced by anaerobic fermentation and contributes to foul odor in infections?

Carbon monoxide
Short-chain fatty acids (butyrate, propionate) and volatile sulfur compounds
Ammonia only
Ozone

Correct Answer: Short-chain fatty acids (butyrate, propionate) and volatile sulfur compounds

Q42. How does the MPN (Most Probable Number) method apply to anaerobic bacteria?

It cannot be used for anaerobes
It estimates viable counts by serial dilution in anaerobic broth with observed growth patterns
It counts individual colonies on aerobic plates
It measures turbidity of aerobic cultures only

Correct Answer: It estimates viable counts by serial dilution in anaerobic broth with observed growth patterns

Q43. Which antibiotic susceptibility pattern is commonly seen in Bacteroides fragilis group?

Pan-susceptible to all beta-lactams
Often resistant to penicillin and some beta-lactams due to beta-lactamase production
Always susceptible to clindamycin
Intrinsic resistance to metronidazole

Correct Answer: Often resistant to penicillin and some beta-lactams due to beta-lactamase production

Q44. What is the role of hydrogen in anaerobic jar systems?

Hydrogen sterilizes the media
Hydrogen reacts with oxygen on the catalyst to remove oxygen from the atmosphere
Hydrogen provides carbon source for bacteria
Hydrogen indicators change color to show anaerobiosis

Correct Answer: Hydrogen reacts with oxygen on the catalyst to remove oxygen from the atmosphere

Q45. Which property helps distinguish anaerobic gram-positive cocci such as Peptostreptococcus from aerobic streptococci?

Growth under strict aerobic conditions
They are anaerobic and often bile-sensitive or variable in hemolysis patterns while streptococci are aerobic or facultative
Presence of endospores
Motility on wet mount

Correct Answer: They are anaerobic and often bile-sensitive or variable in hemolysis patterns while streptococci are aerobic or facultative

Q46. During anaerobic cultivation, what is the purpose of overlaying plates with sterile mineral oil in some assays?

To provide nutrients
To prevent diffusion of antibiotics
To reduce oxygen diffusion to colonies and protect microaerophilic growth
To enhance colony pigmentation

Correct Answer: To reduce oxygen diffusion to colonies and protect microaerophilic growth

Q47. Why is metronidazole effective against many anaerobes?

It inhibits cell wall synthesis
It is reduced to active radicals in anaerobic cells causing DNA damage
It binds to ribosomes to block protein synthesis in aerobes only
It raises redox potential of the cell

Correct Answer: It is reduced to active radicals in anaerobic cells causing DNA damage

Q48. Which control organism might be used to verify anaerobic conditions and culture performance?

Escherichia coli
Clostridium sporogenes or Bacteroides fragilis as biological controls
Pseudomonas aeruginosa
Staphylococcus aureus

Correct Answer: Clostridium sporogenes or Bacteroides fragilis as biological controls

Q49. What is a limitation of using swabs (without anaerobic transport) for anaerobic culture?

Swabs always improve anaerobic recovery
They expose organisms to oxygen and reduce viability of strict anaerobes
Swabs select for anaerobes over aerobes
Swabs sterilize the specimen

Correct Answer: They expose organisms to oxygen and reduce viability of strict anaerobes

Q50. In an anaerobic laboratory workflow, what is the best practice to minimize oxygen exposure during plate handling?

Open plates on bench for extended inspection
Perform inoculation and transfers inside anaerobic chamber or quickly transfer plates to anaerobic jar/workstation and minimize exposure time
Incubate plates in air for initial 1 hour
Leave culture plates uncovered during incubation

Correct Answer: Perform inoculation and transfers inside anaerobic chamber or quickly transfer plates to anaerobic jar/workstation and minimize exposure time

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com

Leave a Comment Cancel reply