**Question:** A child presents with sepsis. Bacteria isolated showed beta hemolysis on blood agar, resistance to bacitracin, and a positive CAMP test. The most probable organism causing infection is -

A. Streptococcus pyogenes
B. Staphylococcus aureus
C. Bacillus licheniformis
D. Clostridium perfringens

**Correct Answer:** **D. Clostridium perfringens**

**Core Concept:**
Beta hemolysis on blood agar indicates the bacteria is a member of the Clostridiales order, which includes anaerobic bacteria. Resistance to bacitracin indicates it is a gram-positive bacteria, as bacitracin is a penicillinase inhibitor used to test for gram-positive bacteria. The positive CAMP test further supports the diagnosis, as it is a specific test for Clostridium species.

**Why the Correct Answer is Right:**
Clostridium perfringens is a gram-positive, anaerobic bacterium that belongs to the Clostridiales order. Its beta hemolysis on blood agar confirms its presence. Resistance to bacitracin is due to the production of a penicillinase enzyme, which is specific to gram-positive bacteria. Additionally, the positive CAMP test is a clue to the diagnosis, as this test is specific for Clostridium species.

**Why Each Wrong Option is Incorrect:**
A. Streptococcus pyogenes (Strep A) is a gram-positive bacteria but typically does not cause beta hemolysis on blood agar. It is also sensitive to bacitracin and does not have a positive CAMP test.
B. Staphylococcus aureus (Staph A) is a gram-positive bacteria, but it usually does not cause beta hemolysis on blood agar and is sensitive to bacitracin. The CAMP test is negative for Staphylococcus species.
C. Bacillus licheniformis is a gram-positive bacteria but does not cause beta hemolysis on blood agar. It is also sensitive to bacitracin and does not have a positive CAMP test.
D. Clostridium perfringens is the correct answer as mentioned above due to its beta hemolysis on blood agar, resistance to bacitracin, and positive CAMP test.

**Clinical Pearls:**
1. Beta hemolysis on blood agar is a characteristic feature of Clostridium species.
2. The CAMP test is specific for Clostridium species, and its result helps in distinguishing it from other gram-positive anaerobes.
3. Bacitracin resistance is a common feature of Clostridium species, unlike Staphylococcus or Streptococcus species.
4. The combination of beta hemolysis, bacitracin resistance, and a positive CAMP test helps to identify Clostridium perfringens as the most probable cause of the infection in this case.