A child presents with infective skin lesion of the leg. Culture showed hemolytic colonies which were gram + ve cocci in chains. The test to confirm the organism is
**Core Concept**
The child's presentation of an infective skin lesion with gram-positive cocci in chains is suggestive of a Streptococcal infection. The presence of hemolytic colonies indicates that the organism is capable of breaking down red blood cells, which is a characteristic of certain Streptococcus species.
**Why the Correct Answer is Right**
The test to confirm the organism is a CAMP test, which is used to differentiate between Group A beta-hemolytic Streptococcus (GABHS) and other beta-hemolytic streptococci. The CAMP test is a radial streak test that detects the production of a hemolysin called streptolysin O, which is produced by GABHS. The test is performed by streaking a sample of the organism on a blood agar plate and then streaking a known source of staphylococcal hemolysin (e.g., Staphylococcus aureus) in a perpendicular direction. If the streptococcal isolate produces streptolysin O, a zone of enhanced hemolysis will appear at the intersection of the two streaks.
**Why Each Wrong Option is Incorrect**
**Option A:** The Coagulase test is used to identify Staphylococcus aureus, which is not the organism described in this scenario.
**Option B:** The Bacitracin sensitivity test is used to identify Group A beta-hemolytic Streptococcus (GABHS), but it is not the most specific test for this purpose.
**Option C:** The Optochin sensitivity test is used to identify Streptococcus pneumoniae, which is not the organism described in this scenario.
**Clinical Pearl / High-Yield Fact**
Remember that the CAMP test is a key diagnostic tool for differentiating between Group A beta-hemolytic Streptococcus (GABHS) and other beta-hemolytic streptococci. This is particularly important in cases of skin and soft tissue infections, where GABHS is a common cause of disease.
**Correct Answer:** C.