Which organism's identification utilizes the reverse CAMP test, lecithinase production, double-zone hemolysis, and characteristic gram stain morphology?

Which organism's identification utilizes the reverse CAMP test, lecithinase production, double-zone hemolysis, and characteristic gram stain morphology?

• A. Streptococcus agalactiae
• B. Propionibacterium acnes
• C. Bacillus anthracis
• D. Clostridium perfringens

Answer: (D)

These findings point to Clostridium perfringens, an anaerobic Gram-positive rod that forms toxins. The reverse CAMP test is a distinguishing feature for this organism: unlike the classic CAMP reaction seen with Group B Streptococcus, C. perfringens shows a reversed reaction when tested with a CAMP-positive organism, helping separate it from other gram-positive rods. Lecithinase production, demonstrated by a zone of opacity around colonies on egg yolk agar, reflects the alpha toxin’s phospholipase activity that breaks down lecithin. Double-zone hemolysis on blood agar—an outer complete (beta) hemolysis with an inner zone of partial (alpha) hemolysis—is another classic clue. Finally, the Gram stain morphology matches: a large Gram-positive rod, typically anaerobic, often with spore formation. Together, these features are characteristic of Clostridium perfringens, whereas the other organisms would not consistently show this exact combination of tests and cellular appearance.

These findings point to Clostridium perfringens, an anaerobic Gram-positive rod that forms toxins. The reverse CAMP test is a distinguishing feature for this organism: unlike the classic CAMP reaction seen with Group B Streptococcus, C. perfringens shows a reversed reaction when tested with a CAMP-positive organism, helping separate it from other gram-positive rods. Lecithinase production, demonstrated by a zone of opacity around colonies on egg yolk agar, reflects the alpha toxin’s phospholipase activity that breaks down lecithin. Double-zone hemolysis on blood agar—an outer complete (beta) hemolysis with an inner zone of partial (alpha) hemolysis—is another classic clue. Finally, the Gram stain morphology matches: a large Gram-positive rod, typically anaerobic, often with spore formation. Together, these features are characteristic of Clostridium perfringens, whereas the other organisms would not consistently show this exact combination of tests and cellular appearance.