Baird Parker Agar 50 FAQs and 30 MCQs
Explore a comprehensive guide on Baird Parker Agar, a selective medium used for isolating Staphylococcus aureus. This page provides 50 frequently asked questions (FAQs) and 30 multiple-choice questions (MCQs) to enhance your understanding of its composition, principle, preparation, and applications in microbiology labs. Perfect for students, lab technicians, and researchers looking to deepen their knowledge of microbiological culture media.
Baird Parker Agar 50 FAQs:
What is Baird Parker Agar used for?
It is used for the selective isolation and enumeration of coagulase-positive staphylococci (e.g., Staphylococcus aureus) from food and clinical samples.
Who developed Baird Parker Agar?
It was developed by Baird-Parker based on Zebovitz’s tellurite-glycine formulation.
Is Baird Parker Agar selective or differential?
It is both selective (inhibits most bacteria except staphylococci) and differential (identifies S. aureus via egg yolk reaction and tellurite reduction).
What makes Baird Parker Agar selective?
Lithium chloride, potassium tellurite, and glycine inhibit most bacteria except Staphylococcus.
How does Baird Parker Agar differentiate S. aureus?
S. aureus produces black colonies (tellurite reduction) with a clear zone (lecithinase activity) and sometimes an opaque ring (lipolysis).
What is the role of egg yolk in Baird Parker Agar?
It provides lecithin, which helps detect lecithinase activity (clear zones around colonies).
Why is sodium pyruvate added to the medium?
It helps recover damaged S. aureus cells and stimulates their growth.
What is the purpose of potassium tellurite?
It inhibits most bacteria and turns staphylococcal colonies black due to tellurite reduction.
What is the pH of Baird Parker Agar?
pH 7.0 ± 0.2 (some formulations may vary slightly).
Which organizations recommend Baird Parker Agar?
AOAC International, USP, ISO, FDA-BAM, and APHA recommend it for staphylococcal detection.
How do you prepare Baird Parker Agar?
Suspend 63g per liter, boil, autoclave (121°C, 15 min), cool to 50°C, then add egg yolk emulsion (50 mL) and potassium tellurite (3 mL).
Can Baird Parker Agar be stored?
Yes, store at 4-8°C (shelf life: 6 weeks for prepared plates).
What supplements can be added to Baird Parker Agar?
Egg Yolk Tellurite Emulsion, Sulfamethazine (for Proteus inhibition), or RPF Supplement (for coagulase detection).
How much sample should be plated?
Typically 0.1 mL is spread on the agar surface.
What incubation conditions are required?
35-37°C for 24-48 hours, aerobically.
How do you interpret results after 24 hours?
Look for black, shiny, convex colonies (1-1.5 mm) with a clear zone (presumptive S. aureus).
What if no colonies appear after 24 hours?
Re-incubate for another 24 hours before final interpretation.
Can Baird Parker Agar be used for MPN (Most Probable Number) testing?
Yes, in combination with Giolitti Cantoni Broth for low-level detection.
How does RPF Supplement improve detection?
It contains fibrinogen and plasma, allowing coagulase-positive colonies to form halos.
What is the alternative to Egg Yolk Tellurite Emulsion?
Fibrinogen Plasma Trypsin Inhibitor Supplement can be used for coagulase detection.
What do typical S. aureus colonies look like?
Black/gray, shiny, convex, with a clear halo (sometimes an opaque ring).
What do atypical S. aureus colonies look like?
Similar but without a clear zone (common in dairy products).
What does Staphylococcus epidermidis look like on Baird Parker Agar?
Black colonies, no halo (coagulase-negative).
How does Micrococcus luteus appear?
Small brown-black colonies, no lecithinase activity.
What indicates Proteus mirabilis growth?
Brown-black colonies, no lecithinase reaction.
Can E. coli grow on Baird Parker Agar?
Rarely, but if it does, it forms large brown-black colonies without a halo.
What does Bacillus subtilis look like?
Dark brown, matt colonies, no lecithinase activity.
Do yeasts grow on Baird Parker Agar?
Yes, but they appear as white colonies, no halo.
What if colonies have an opaque zone but no clearing?
Could be lipolytic staphylococci (e.g., S. saprophyticus).
Why must coagulase testing be done for confirmation?
Some non-S. aureus strains may produce similar-looking colonies.
What are the limitations of Baird Parker Agar?
Some non-staphylococci may grow, and coagulase testing is needed for confirmation.
Can Proteus interfere with results?
Yes, but sulfamethazine supplement can inhibit it.
What if background flora obscures colonies?
Use RPF Supplement for better differentiation.
Why do some S. aureus strains not produce clear zones?
Some strains may have weak lecithinase activity.
Can damaged S. aureus cells still grow?
Yes, sodium pyruvate helps recover stressed cells.
What if colonies are too crowded?
Only count plates with 15-300 colonies for accurate enumeration.
Why are some colonies brown instead of black?
Some coagulase-negative staphylococci may only partially reduce tellurite.
Can Baird Parker Agar detect MRSA?
No, additional antibiotic testing is required for MRSA detection.
What if the medium appears too dry?
Ensure proper storage (4-8°C) and avoid excessive drying before use.
Why is autoclaving necessary?
To sterilize the medium and ensure no contaminants interfere.
What QC strains are used for Baird Parker Agar?
S. aureus (ATCC 25923), S. epidermidis (ATCC 14990), E. coli (ATCC 25922).
What is the shelf life of dehydrated Baird Parker Agar?
4 years if stored properly (dry, 10-30°C).
How should prepared plates be stored?
Upside down at 4-8°C to prevent condensation.
Can expired Baird Parker Agar be used?
No, performance may be compromised.
How do you check sterility of the medium?
Incubate a sample plate at 35°C for 24 hours before use.
Is Baird Parker Agar ISO-compliant?
Yes, it follows ISO 6888-1, -2, -3 for staphylococcal enumeration.
Is it used in clinical labs?
Primarily for food testing, but can be adapted for clinical samples.
What is the difference between Baird Parker Agar and Mannitol Salt Agar?
Baird Parker is more selective and detects lecithinase, while MSA detects mannitol fermentation.
Can it be used for water testing?
Yes, for enumeration of S. aureus in water samples.
What is the best confirmatory test after Baird Parker Agar?
Coagulase test (tube or slide) or DNase test for S. aureus confirmation.
Baird Parker Agar 30 MCQs:
- What is the primary purpose of Baird Parker Agar?
a) Isolation of E. coli
b) Enumeration of coagulase-positive staphylococci
c) Detection of Salmonella
d) Culturing fungi - Who developed Baird Parker Agar?
a) Robert Koch
b) Louis Pasteur
c) Baird-Parker
d) Joseph Lister - Which component in Baird Parker Agar helps recover damaged S. aureus cells?
a) Lithium chloride
b) Sodium pyruvate
c) Potassium tellurite
d) Glycine - What is the role of potassium tellurite in Baird Parker Agar?
a) Provides nutrients for bacterial growth
b) Inhibits most bacteria and turns S. aureus colonies black
c) Acts as a pH indicator
d) Enhances fungal growth - Which enzyme activity is detected by the egg yolk in Baird Parker Agar?
a) Catalase
b) Lecithinase
c) Oxidase
d) Amylase
- What is the final pH of Baird Parker Agar?
a) 5.5 ± 0.2
b) 6.0 ± 0.2
c) 7.0 ± 0.2
d) 8.0 ± 0.2 - Which of the following is NOT a component of Baird Parker Agar?
a) Tryptone
b) Sodium pyruvate
c) Mannitol
d) Lithium chloride - How is Baird Parker Agar sterilized?
a) Filtration
b) Autoclaving at 121°C for 15 minutes
c) UV radiation
d) Boiling for 10 minutes - What supplement is added to detect coagulase-positive staphylococci without egg yolk?
a) RPF Supplement
b) Sulfamethazine
c) DNase reagent
d) Oxidase reagent - How much egg yolk emulsion is added per liter of Baird Parker Agar?
a) 5 mL
b) 50 mL
c) 100 mL
d) 200 mL
- What is the typical appearance of S. aureus on Baird Parker Agar?
a) White, fuzzy colonies
b) Black, shiny colonies with a clear halo
c) Green, metallic sheen colonies
d) Red, mucoid colonies - Which organism grows as black colonies but does NOT produce a clear zone?
a) Staphylococcus aureus
b) Staphylococcus epidermidis
c) Proteus mirabilis
d) Escherichia coli - What does an opaque zone around S. aureus colonies indicate?
a) Protease activity - b) Lipolytic activity
c) Hemolysis
d) Urease production - Which organism is completely inhibited on Baird Parker Agar?
a) Staphylococcus aureus
b) Escherichia coli
c) Micrococcus luteus
d) Bacillus subtilis - What should be done if colonies resemble S. aureus but lack a clear zone?
a) Discard the result
b) Perform a coagulase test for confirmation
c) Incubate for another 72 hours
d) Add more potassium tellurite
- Which regulatory body recommends Baird Parker Agar for food testing?
a) WHO
b) CDC
c) AOAC International
d) NIH - What is the main limitation of Baird Parker Agar?
a) It cannot detect S. aureus
b) Some non-staphylococci may grow
c) It requires anaerobic incubation
d) It turns all bacteria black - Which supplement is used to inhibit Proteus spp. on Baird Parker Agar?
a) RPF Supplement
b) Sulfamethazine
c) Egg Yolk Emulsion
d) Sodium pyruvate - For how long should Baird Parker Agar plates be incubated?
a) 12 hours
b) 24-48 hours
c) 72 hours
d) 1 week - Which method is used for low-level detection of S. aureus using Baird Parker Agar?
a) Direct plating
b) MPN (Most Probable Number)
c) Gram staining
d) PCR
- Which component enhances the selectivity of Baird Parker Agar?
a) Glycine
b) Sodium chloride
c) Glucose
d) Phenol red - What is the shelf life of prepared Baird Parker Agar plates?
a) 1 week
b) 6 weeks
c) 6 months
d) 1 year - Which Staphylococcus species may produce an opaque zone but is coagulase-negative?
a) S. aureus
b) S. epidermidis
c) S. saprophyticus
d) S. haemolyticus - What is the purpose of lithium chloride in Baird Parker Agar?
a) Stimulates S. aureus growth
b) Inhibits Gram-negative bacteria
c) Acts as a pH buffer
d) Enhances pigment production - Which ISO standard specifies the use of Baird Parker Agar?
a) ISO 6579
b) ISO 6888
c) ISO 21528
d) ISO 4833 - What should be done if Proteus overgrowth occurs on Baird Parker Agar?
a) Repeat with higher dilution
b) Add sulfamethazine
c) Incubate at 25°C
d) Use Mannitol Salt Agar instead - Which organism appears as dark brown, matt colonies on Baird Parker Agar?
a) Bacillus subtilis
b) Escherichia coli
c) Micrococcus luteus
d) Staphylococcus aureus - What is the confirmatory test for S. aureus after isolation on Baird Parker Agar?
a) Oxidase test
b) Coagulase test
c) Indole test
d) Citrate test - Which medium is an alternative to Baird Parker Agar for S. aureus detection?
a) MacConkey Agar
b) Mannitol Salt Agar
c) Blood Agar
d) Sabouraud Dextrose Agar - What does a clear zone around colonies on Baird Parker Agar indicate?
a) Hemolysis
b) Lecithinase activity
c) Urease activity
d) Catalase activity
Baird Parker Agar is a specialized culture medium designed for the selective isolation and differentiation of Staphylococcus aureus and other coagulase-positive staphylococci. Its formulation includes a base of peptones, glycine, lithium chloride, and sodium pyruvate, supplemented with egg yolk tellurite emulsion. The tellurite acts as an inhibitory agent against most Gram-positive and Gram-negative bacteria, while the egg yolk helps differentiate S. aureus from other species based on colony morphology.
On Baird Parker Agar, Staphylococcus aureus typically forms black, shiny colonies with a clear halo due to lipase activity and an opaque zone from proteolytic reactions. In contrast, Staphylococcus epidermidis produces black colonies without a halo, and Gram-negative bacteria like E. coli are generally inhibited. The medium is widely used in food microbiology, clinical diagnostics, and environmental testing to detect pathogenic staphylococci.
Several commercial brands, including HiMedia, Oxoid, Merck, and BioKar, produce Baird Parker Agar with slight variations in composition. The medium is prepared by autoclaving the base, cooling it, and then adding sterile egg yolk tellurite before pouring into plates. Incubation is typically carried out at 35–37°C for 24–48 hours. Due to its selective and differential properties, Baird Parker Agar remains a gold standard for S. aureus detection in laboratory settings.
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