A child has respiratory infection with membrane over Peritonsillar area. Swab was taken from the local area. The appropriate media for culture is –
**Core Concept**
The question is testing the knowledge of the appropriate culture medium for a specific pathogen, which is likely to be *Streptococcus pyogenes* given the clinical presentation. The peritonsillar area is commonly affected by this bacterium, leading to peritonsillar abscess or cellulitis.
**Why the Correct Answer is Right**
The culture medium of choice for *S. pyogenes* is the Thayer-Martin medium, but since it is not listed, it is likely that the correct answer is Blood agar. Blood agar is a rich medium that supports the growth of *S. pyogenes*, which is a beta-hemolytic streptococcus. The bacteria produce beta-hemolysis, which appears as a clear zone around the colonies. This medium is suitable for the isolation and identification of *S. pyogenes* from clinical specimens.
**Why Each Wrong Option is Incorrect**
- **Option A:** MacConkey agar is a selective medium for gram-negative bacteria, particularly *Escherichia coli* and other enteric pathogens. It is not the medium of choice for *S. pyogenes*.
- **Option B:** Mannitol salt agar is a selective medium for *Staphylococcus aureus*, which is a gram-positive coccus that produces golden colonies on this medium. It is not suitable for *S. pyogenes*.
- **Option C:** Chocolate agar is a medium enriched with V factor (nicotinamide adenine dinucleotide) and is used to culture *Haemophilus influenzae*. It is not the medium of choice for *S. pyogenes*.
**Clinical Pearl / High-Yield Fact**
When culturing *S. pyogenes*, it is essential to note that this bacterium is a beta-hemolytic streptococcus, which means it produces a clear zone around the colonies on blood agar. This characteristic is a key identifying feature of *S. pyogenes*.
**Correct Answer:** D. Blood agar.