Chocolate Agar in Pakistan

Here are the key specifications for Chocolate Agar (CHOC) — the enriched agar medium often used in microbiology labs.

🍫 Description & Purpose

• Chocolate Agar is a variant of blood agar in which red blood cells have been lysed (by heating) to release intracellular nutrients (e.g., hemin = “X factor”, and NAD = “V factor”).
• Because those factors are now freely available, CHOC supports the growth of fastidious bacteria such as Haemophilus influenzae and Neisseria gonorrhoeae.
• It is non-selective in its basic form (i.e., it allows many organisms to grow) unless further antibiotics or supplements are added.

🧪 Composition (typical formulation)

Here are typical ingredient values (may vary by manufacturer).

• Casein / animal tissue digest: ~15.0 g/L
• Cornstarch: ~1.0 g/L
• Sodium chloride (NaCl): ~5.0 g/L
• Dipotassium phosphate (K₂HPO₄): ~4.0 g/L
• Monopotassium phosphate (KH₂PO₄): ~1.0 g/L
• Agar: ~10.0 g/L (in some formulations)
• Hemoglobin solution (or “chocolatised blood”): e.g., 500 mL of 2% hemoglobin / L.
• Supplement(s) (e.g., NAD, hemin) may be added.
• pH: ~7.2 ± 0.2 at 25 °C for many recipes.

Example specification from a commercial product:

• Special Peptone 23.0 g/L
• Starch 1.0 g/L
• Sodium chloride 5.0 g/L
• Agar No.1 10.0 g/L
• Cocarboxylase 0.01 g/L
• Glucose 5.0 g/L
• Chocolate supplement ~6.6 mL/L
• Horse blood (chocolatised) ~80 mL/L
• Final pH 7.4 ± 0.2.

🔬 Preparation / Incubation Notes

• The red blood cells are added (or hemoglobin solution) and then heated to lyse the cells and liberate the growth factors.
• After pouring plates, typical incubation conditions for fastidious organisms: ~35-37 °C, often with 5 % CO₂ atmosphere.
• Storage of prepared plates: e.g., store at 2-8 °C, protected from light, until use.

✅ Uses & Limitations

Uses:

• Isolation and cultivation of fastidious organisms (e.g., Haemophilus spp., Neisseria spp.).
• Non-selective enrichment medium: good for general recovery of fastidious bacteria when you don’t want to suppress background flora.

Limitations:

• Because it is enriched and non-selective, background/commensal organisms may overgrow target pathogens.
• For selective isolation (e.g., of Neisseria gonorrhoeae), one often uses a modified medium (e.g., Thayer‑Martin Agar) that suppresses non-target organisms.
• Appearance of dark spots (precipitated hemoglobin) may occur but do not affect performance.

📋 Quick‐Specs Summary Table

If you like, I can pull in manufacturer-specific specs (for several brands) so you can compare exact formulations for your lab. Would you like that?