Thioglycollate Broth 50 FAQs and 30 MCQs
Master Thioglycollate Broth, the versatile enriched medium for culturing aerobic, anaerobic, and microaerophilic organisms, with this comprehensive guide. Perfect for microbiologists, lab technicians, and medical students, this resource combines 50 expert FAQs and 30 practice MCQs to enhance your diagnostic skills.
📌 What’s Covered?
✅ 50 Essential FAQs
✔ Principle & Composition:
- Sodium thioglycollate (reducing agent)
- Resazurin (oxygen indicator)
- Nutrient-rich base for fastidious organisms
✔ Clinical Applications: - Blood cultures (supports Bacteroides, Clostridium)
- Wound/pus specimen processing
- QC for sterility testing
✔ Protocol Optimization: - Proper inoculation techniques
- Incubation conditions (35-37°C, 5-7 days)
- Oxygen gradient interpretation
✔ Troubleshooting: - Pink discoloration (oxygen exposure)
- Overgrowth by contaminants
✅ 30 Challenging MCQs
◼️ Identifying growth patterns (aerobic vs. anaerobic zones)
◼️ Resazurin indicator interpretation
◼️ Comparing Thioglycollate vs. Robertson’s Cooked Meat Broth
◼️ CLSI guidelines for sterility testing
🎯 Perfect For:
- Clinical microbiologists (ASCP certification)
- Medical lab technicians (MLT/MLS)
- Infection control specialists
Thioglycollate Broth 50 FAQs
What is Thioglycollate Broth?
A multipurpose enriched differential medium used to determine oxygen requirements of microorganisms.
What types of microorganisms can grow in Thioglycollate Broth?
Aerobes, anaerobes, microaerophiles, and fastidious bacteria.
What is the primary purpose of Thioglycollate Broth?
To differentiate bacteria based on their oxygen requirements.
Is Thioglycollate Broth selective or differential?
It is differential (distinguishes bacteria based on oxygen needs) and enriched (supports fastidious microbes).
What is the pH range of Thioglycollate Broth?
7.1 ± 0.2 (may vary slightly by formulation).
What are the key ingredients in Thioglycollate Broth?
Casein digest, yeast extract, glucose, sodium thioglycollate, L-cystine, sodium chloride.
Why is sodium thioglycollate added?
Acts as a reducing agent, neutralizing oxygen and peroxides to create anaerobic conditions.
What is the role of L-cystine in the medium?
Helps reduce oxygen levels and supports the growth of strict anaerobes like Clostridium
Why is glucose included in Thioglycollate Broth?
Provides an energy source for bacterial growth.
Does Thioglycollate Broth contain agar?
Some formulations include 0.075% agar to prevent convection currents, but not all.
What is the function of resazurin in some formulations?
Acts as an oxidation-reduction indicator (pink when oxidized, colorless when reduced).
Why is yeast extract added?
Provides essential growth factors (vitamins, amino acids) for fastidious bacteria.
How does Thioglycollate Broth neutralize heavy metals?
Sulfhydryl groups in thioglycollate and L-cystine bind and detoxify heavy metals.
How is Thioglycollate Broth prepared?
29g per liter of distilled water, boiled, dispensed, and autoclaved at 121°C for 15 min.
Why should the medium be freshly prepared or reheated before use?
To remove absorbed oxygen and prevent oxidation.
Can Thioglycollate Broth be reheated multiple times?
No, reheating forms toxic oxygen radicals.
How should Thioglycollate Broth be stored?
Upright, sealed, protected from light at 15-25°C.
What indicates that the medium is oxidized and unusable?
A pink band (from resazurin) extending beyond the surface.
How can oxidized Thioglycollate Broth be restored?
Boil for 15 min (with loosened cap) to drive off oxygen.
What is the shelf life of prepared Thioglycollate Broth?
Up to 2 years if stored properly (unless oxidized).
How should Thioglycollate Broth be inoculated?
Using aseptic technique, ensuring the sample reaches the bottom.
Why is overlaying with paraffin or agar sometimes done?
To enhance anaerobiosis by blocking oxygen diffusion.
What is the recommended incubation temperature?
30-35°C for several days.
How long should Thioglycollate Broth be incubated?
Typically 3-14 days, depending on the organism.
Can Thioglycollate Broth be used for blood cultures?
Yes, but blood must be diluted 1:10 to prevent clotting.
Where do obligate aerobes grow in Thioglycollate Broth?
Top (high oxygen concentration).
Where do obligate anaerobes grow?
Bottom (low/no oxygen).
How do facultative anaerobes appear in the tube?
Throughout, but denser at the top (more ATP from aerobic respiration).
Where do microaerophiles grow?
Upper-middle (need oxygen but are poisoned by high levels).
How do aerotolerant organisms distribute?
Evenly spread (not affected by oxygen).
What does turbid growth indicate?
Bacterial proliferation (e.g., E. coli, S. aureus).
What does flocculent growth indicate?
Yeasts (e.g., Candida albicans).
How can you detect contamination in Thioglycollate Broth?
Turbidity, color change, gas production, or hemolysis.
Why might some anaerobes fail to grow?
Oxygen contamination, expired medium, or improper storage.
What are the main uses of Thioglycollate Broth?
Sterility testing, anaerobic culture, oxygen requirement studies.
Is Thioglycollate Broth used in pharmaceutical testing?
Yes, for sterility tests (USP/EP compliance).
Can it be used for food microbiology?
Yes, for detecting anaerobic contaminants.
Why is it preferred for isolating Clostridium species?
Supports strict anaerobes via reducing agents.
Can Thioglycollate Broth replace Fluid Thioglycollate Medium (FTM)?
Yes, but FTM contains agar and resazurin.
What are the limitations of Thioglycollate Broth?
Cannot be reheated multiple times, requires fresh preparation.
Why should it not be stored at low temperatures?
Increases oxygen absorption.
What if the medium turns pink before use?
Discard or reheat (indicates oxidation).
Why might facultative anaerobes grow poorly?
Over-oxidation, insufficient nutrients, or incorrect pH.
Can Thioglycollate Broth detect all anaerobes?
No, some may require additional supplements (e.g., hemin, vitamin K).
Which standards approve Thioglycollate Broth?
USP, European Pharmacopeia, APHA.
What are some QC strains used for testing?
Clostridium sporogenes, Bacillus subtilis, Pseudomonas aeruginosa.
What is the expected result for Bacteroides vulgatus?
Turbid growth (anaerobic region).
How is sterility testing performed with this medium?
Inoculate and monitor for microbial growth over 14 days.
How is Thioglycollate Broth disposed of safely?
Autoclave (121°C, 20 min) before disposal.
Where can Thioglycollate Broth be purchased?
From microbiological suppliers (e.g., Merck, Sigma-Aldrich).
Thioglycollate Broth 30 MCQs
- What is the primary purpose of Thioglycollate Broth?
a) To differentiate bacteria based on sugar fermentation
b) To determine oxygen requirements of microorganisms
c) To selectively grow Gram-positive bacteria
d) To inhibit fungal growth - Which ingredient in Thioglycollate Broth acts as a reducing agent?
a) Glucose
b) Sodium thioglycollate
c) Yeast extract
d) Agar - What is the role of L-cystine in Thioglycollate Broth?
a) Provides carbon source
b) Neutralizes peroxides and supports anaerobes
c) Acts as a pH indicator
d) Inhibits Gram-negative bacteria - What does resazurin indicate in Thioglycollate Broth?
a) pH change
b) Oxygen presence (pink = oxidized)
c) Glucose fermentation
d) Protein digestion - Why is agar (0.075%) sometimes added to Thioglycollate Broth?
a) To solidify the medium
b) To prevent convection currents
c) To enhance bacterial motility
d) To inhibit anaerobes
- How is Thioglycollate Broth sterilized?
a) Filtration
b) Autoclaving at 121°C for 15 minutes
c) Boiling for 5 minutes
d) UV radiation - What should be done if the medium turns pink before use?
a) Discard it
b) Reheat it to remove oxygen
c) Add more glucose
d) Adjust pH with HCl - Why should Thioglycollate Broth not be stored at low temperatures?
a) It solidifies
b) Increases oxygen absorption
c) Kills bacteria
d) Changes color - What is the shelf life of properly stored Thioglycollate Broth?
a) 1 month
b) 6 months
c) 2 years
d) Indefinite - How should Thioglycollate Broth be stored?
a) Frozen
b) Upright, sealed, and protected from light
c) In direct sunlight
d) With loose caps
- Where do obligate aerobes grow in Thioglycollate Broth?
a) Bottom
b) Middle
c) Top
d) Evenly throughout - Obligate anaerobes grow predominantly in which zone?
a) Surface
b) Middle
c) Bottom
d) Uniformly - Facultative anaerobes show growth:
a) Only at the top
b) Only at the bottom
c) Throughout, but denser at the top
d) In a single colony - Microaerophiles grow best:
a) At the very top
b) Just below the surface
c) At the bottom
d) In a zigzag pattern - What does flocculent growth in Thioglycollate Broth indicate?
a) Bacterial contamination
b) Fungal/yeast growth (e.g., Candida)
c) Viral infection
d) No growth
- Thioglycollate Broth is used for sterility testing of:
a) Antibiotics
b) Blood cultures
c) Food samples
d) All of the above - Which standard recommends Thioglycollate Broth for sterility tests?
a) USP (United States Pharmacopeia)
b) FDA
c) CDC
d) WHO - Why is blood diluted 1:10 in Thioglycollate Broth for cultures?
a) To prevent clotting
b) To enhance oxygen levels
c) To inhibit bacteria
d) To reduce turbidity - Which organism is commonly tested in QC for Thioglycollate Broth?
a) Escherichia coli
b) Clostridium sporogenes
c) Staphylococcus epidermidis
d) Pseudomonas fluorescens - Thioglycollate Broth is NOT suitable for:
a) Growing viruses
b) Differentiating oxygen requirements
c) Cultivating anaerobes
d) Sterility testing
- Reheating Thioglycollate Broth multiple times can lead to:
a) Better anaerobiosis
b) Toxic oxygen radicals
c) Increased nutrient levels
d) Longer shelf life - If the medium is pink throughout, it indicates:
a) Proper anaerobic conditions
b) Complete oxidation (unsuitable for anaerobes)
c) Bacterial growth
d) pH imbalance - Which of the following is a limitation of Thioglycollate Broth?
a) Cannot support fastidious bacteria
b) Must be freshly prepared or reheated before use
c) Only grows aerobic bacteria
d) Turns blue when sterile - What supplement might be needed for fastidious anaerobes?
a) Hemin and vitamin K
b) Sodium chloride
c) Phenol red
d) Lactose - Why is sodium thioglycollate added to the medium?
a) To increase pH
b) To neutralize heavy metals
c) To solidify the broth
d) To inhibit Gram-positives
- Which organism grows as “puffballs” in Thioglycollate Broth?
a) E. coli
b) Streptococcus pneumoniae
c) Pseudomonas aeruginosa
d) Bacteroides fragilis - What is the purpose of the pancreatic digest of casein?
a) To provide nitrogen and amino acids
b) To act as a reducing agent
c) To inhibit fungi
d) To change color with pH - Which bacteria would grow at the top of the tube?
a) Clostridium perfringens
b) Micrococcus luteus
c) Bacteroides vulgatus
d) Peptostreptococcus anaerobius - What is the correct incubation temperature for Thioglycollate Broth?
a) 25°C
b) 30-35°C
c) 42°C
d) 4°C - Which regulatory body does NOT reference Thioglycollate Broth?
a) USP
b) European Pharmacopeia
c) CDC
d) APHA
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