**Question:** A child presents with infective skin lesion of the leg. A culture was done which showed gram+ve cocci in chains which were hemolytic colonies. The test to confirm the organism is

A. Coagulase test
B. Voges-Proskauer test
C. Capsule production test
D. Arthritis

**Correct Answer:** .

**Core Concept:**
Gram-positive cocci in chains, with hemolysis on culture, suggest the presence of Staphylococcus species. These organisms are commonly associated with skin infections, particularly in immunocompromised children. The key tests to confirm the identity of these organisms are those that specifically test for the presence of coagulase enzyme.

**Why the Correct Answer is Right:**
The correct answer is the Coagulase test (Option A). The coagulase test is essential to confirm the presence of Staphylococcus aureus, a common causative agent of skin infections. Staphylococci are gram-positive cocci that form chains and exhibit beta-hemolysis on blood agar plates. The coagulase test is a crucial step in confirming the identity of the organism because:

1. Coagulase is an enzyme produced by Staphylococcus aureus that converts fibrinogen into fibrin.
2. The test involves mixing the organism with plasma and observing clot formation.
3. If the organism is positive for coagulase, it will cause clot formation, indicating the presence of Staphylococcus aureus.

**Why Each Wrong Option is Incorrect:**

A. The Voges-Proskauer test (Option B) is used to identify Clostridium perfringens, which is not the causative agent of the described skin infection.

C. Capsule production test (Option C) is used to differentiate between different serotypes of Streptococcus pneumoniae, not Staphylococcus aureus, which is the organism in question.

D. Arthritis (Option D) is a clinical manifestation of staphylococcal infections, not a test for the identification of the causative organism.

**Clinical Pearl:**

Staphylococcus aureus is a significant pathogen causing skin infections in children, particularly in immunocompromised individuals. Early identification of Staphylococcus aureus is crucial for appropriate antibiotic therapy and patient management. The coagulase test is the gold standard for confirming the presence of Staphylococcus species and differentiating them from other gram-positive organisms.