Microbial Culture Media 50 FAQs and 30 MCQs:
Microbial Culture Media 50 FAQs:
What is microbial culture media?
A nutrient-rich substance used to grow microorganisms in labs.
What are the main components of culture media?
Peptone, beef extract, yeast extract, agar, and distilled water.
What is the role of agar in culture media?
It acts as a solidifying agent (1.5-2% for solid media).
What is the difference between defined and undefined media?
Defined media have known quantities of ingredients, while undefined media contain complex, variable components.
Why is sterilization important in media preparation?
To prevent contamination by unwanted microbes (autoclaving at 121°C, 15 psi for 15 min).
What are the three physical states of culture media?
Solid, semi-solid, and liquid media.
What is the purpose of semi-solid media?
To study bacterial motility (e.g., Mannitol motility media).
What is nutrient broth?
A liquid medium without agar for growing bacteria.
What is selective media?
Promotes growth of specific microbes while inhibiting others (e.g., MacConkey agar).
What is differential media?
Differentiates microbes based on biochemical reactions (e.g., Blood agar for hemolysis).
What is enriched media?
Contains extra nutrients (e.g., blood, serum) for fastidious organisms (e.g., Chocolate agar).
What is transport media?
Preserves specimens during transport (e.g., Stuart’s medium).
What is anaerobic media?
Supports growth of anaerobic bacteria (e.g., Robertson cooked meat medium).
What is minimal media?
Contains only essential nutrients for wild-type microbes.
What is resuscitation media?
Helps recover stressed or damaged bacteria.
How is culture media prepared?
Weigh ingredients → Dissolve in water → Adjust pH → Add agar → Autoclave → Pour into plates.
Why is pH adjustment important?
Different microbes require specific pH ranges for optimal growth.
What is the purpose of autoclaving?
To sterilize media by killing all microbes (121°C, 15 psi, 15 min).
Why are Petri plates inverted after pouring media?
To prevent condensation from dripping onto colonies.
How is laminar airflow used in media preparation?
Provides a sterile workspace (disinfected with 70% alcohol).
Why is MacConkey agar used?
Selective for Gram-negative bacteria & differentiates lactose fermenters (pink colonies).
What is Blood agar used for?
Detects hemolytic bacteria (alpha, beta, gamma hemolysis).
What is Chocolate agar used for?
Grows fastidious bacteria like Neisseria gonorrhoeae.
What is Lowenstein-Jensen medium for?
Isolates Mycobacterium tuberculosis.
What is Sabouraud agar used for?
Fungal culture (low pH inhibits bacteria).
How is antibiotic sensitivity tested?
Using Mueller-Hinton agar with antibiotic discs (measures zone of inhibition).
What is the role of thioglycollate broth?
Supports aerobic and anaerobic bacteria growth.
Why is Selenite F broth used?
Enriches Salmonella from fecal samples.
What is Cetrimide agar for?
Selective for Pseudomonas aeruginosa.
What is Mannitol Salt Agar (MSA) used for?
Selects Staphylococcus aureus (ferments mannitol → yellow colonies).
Why might media fail to solidify?
Insufficient agar or improper pH.
What causes media contamination?
Improper sterilization or poor aseptic technique.
Why do some bacteria not grow on nutrient agar?
They may require enriched or selective media.
How can drying of media be prevented?
Store plates sealed and refrigerated.
What if no growth occurs after incubation?
Check incubation conditions, media composition, or sample viability.
What is Hektoen Enteric Agar used for?
Differentiates Salmonella (black colonies) and Shigella (green).
What is XLD agar?
Selective for Salmonella and Shigella.
What is BCYE agar?
For Legionella isolation.
What is Thayer-Martin agar?
Selective for Neisseria gonorrhoeae.
What is Baird-Parker agar for?
Isolates Staphylococcus aureus.
How is fermentation media different?
High nutrient concentration for industrial product yield (e.g., alcohol).
What is assay media?
Tests antibiotic/vitamin potency (e.g., Mueller-Hinton for AST)
What is chromogenic media?
Uses color indicators for rapid pathogen ID (e.g., CHROMagar).
Why is cooked meat broth used?
Maintains anaerobic bacteria viability.
What is the use of Cary-Blair medium?
Preserves enteric pathogens in stool samples.
Can media be reused?
No, prepared media should be used fresh to avoid contamination.
How long can prepared media be stored?
2-4 weeks refrigerated (varies by type).
Why is yeast extract used in media?
Provides vitamins, carbon, and nitrogen.
What is the difference between broth and agar?
Broth is liquid; agar is solid/semi-solid.
What are fastidious bacteria?
Microbes requiring specific nutrients (e.g., Haemophilus needs X & V factors).
Microbial Culture Media 30 MCQs:
- What is the primary purpose of microbial culture media?
a) To kill microorganisms
b) To support microbial growth✔
c) To stain bacteria
d) To observe viruses - Which component acts as a solidifying agent in solid media?
a) Peptone
b) Agar✔
c) Beef extract
d) Yeast extract - What is the concentration of agar in solid media?
a) 0.1-0.5%
b) 1.5-2.0%✔
c) 5-10%
d) 20-30% - Which of the following is a liquid medium?
a) Nutrient agar
b) MacConkey agar
c) Nutrient broth✔
d) Blood agar - What is the function of peptone in culture media?
a) Solidifying agent
b) Source of carbon and nitrogen✔
c) pH indicator
d) Selective agent
- Which media is used to isolate fastidious bacteria like Neisseria gonorrhoeae?
a) Nutrient agar
b) Chocolate agar✔
c) MacConkey agar
d) Mannitol salt agar - MacConkey agar is selective for:
a) Gram-positive bacteria
b) Gram-negative bacteria✔
c) Anaerobes
d) Fungi - Which media is used to differentiate lactose fermenters from non-fermenters?
a) Blood agar
b) MacConkey agar✔
c) Nutrient agar
d) Sabouraud agar - Mannitol Salt Agar (MSA) is selective for:
a) E. coli
b) Staphylococcus aureus✔
c) Pseudomonas aeruginosa
d) Salmonella typhi - Which medium is used to grow Mycobacterium tuberculosis?
a) Blood agar
b) Lowenstein-Jensen medium✔
c) MacConkey agar
d) Sabouraud agar
- What is the standard autoclaving condition for sterilizing media?
a) 100°C for 5 min
b) 121°C for 15 min at 15 psi✔
c) 80°C for 30 min
d) 60°C for 1 hour - Why are Petri plates inverted after pouring media?
a) To speed up solidification
b) To prevent condensation from dripping✔
c) To enhance bacterial growth
d) To reduce contamination - Which instrument is used to sterilize media?
a) Incubator
b) Autoclave✔
c) Centrifuge
d) Spectrophotometer - What is the purpose of adjusting pH in media preparation?
a) To make it colorful
b) To optimize microbial growth✔
c) To increase agar concentration
d) To prevent evaporation - Which of the following is NOT a step in media preparation?
a) Weighing ingredients
b) Autoclaving
c) Adding antibiotics before sterilization✔
d) Pouring into Petri plates
- Which medium is used for antibiotic sensitivity testing?
a) Blood agar
b) Chocolate agar
c) Mueller-Hinton agar✔
d) MacConkey agar - What does a zone of inhibition indicate in antibiotic testing?
a) Bacterial growth
b) Resistance to antibiotics
c) Sensitivity to antibiotics✔
d) Contamination - Which medium is used to culture fungi?
a) Nutrient agar
b) Sabouraud agar✔
c) Blood agar
d) MacConkey agar - What is the purpose of enrichment media like Selenite F broth?
a) To kill all bacteria
b) To selectively enhance growth of pathogens (e.g., Salmonella)✔
c) To solidify media
d) To stain bacteria - Which medium is used to test water for coliforms?
a) MacConkey broth✔
b) Nutrient agar
c) Blood agar
d) Chocolate agar
- Why might prepared media appear cloudy?
a) Due to bacterial contamination
b) Because of improper sterilization
c) Due to undissolved agar
d) All of the above✔ - What is the purpose of resuscitation media?
a) To kill bacteria
b) To recover stressed/damaged bacteria✔
c) To solidify media faster
d) To stain bacteria - Which medium is used to test for Clostridium difficile?
a) Blood agar
b) Cycloserine-cefoxitin-fructose agar (CCFA)✔
c) MacConkey agar
d) Nutrient agar - What is the role of bile salts in MacConkey agar?
a) To inhibit Gram-positive bacteria✔
b) To enhance fungal growth
c) To solidify media
d) To increase pH - Which medium is used to transport Vibrio cholerae samples?
a) Cary-Blair medium✔
b) Blood agar
c) Nutrient agar
d) Chocolate agar
- Which medium is used to detect Pseudomonas aeruginosa?
a) Cetrimide agar✔
b) Blood agar
c) MacConkey agar
d) Sabouraud agar - What is the indicator in Mannitol Salt Agar (MSA)?
a) Phenol red✔
b) Methylene blue
c) Neutral red
d) Bromothymol blue - Which medium is used for coagulase test in Staphylococcus?
a) Blood agar
b) Nutrient agar
c) Rabbit plasma agar✔
d) MacConkey agar - What is the purpose of Thiosulfate-Citrate-Bile Salts-Sucrose (TCBS) agar?
a) To isolate Vibrio species✔
b) To grow fungi
c) To test antibiotic resistance
d) To detect E. coli - Which medium is used for the cultivation of Legionella?
a) Blood agar
b) BCYE agar✔
c) MacConkey agar
d) Nutrient agar
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