**Question:** Which non-diphtheria corynebacterium is used as immunomodulator?

A. Corynebacterium parvum
B. Corynebacterium glutamicum
C. Corynebacterium diptheriae
D. Propionibacterium acnes

**Correct Answer:** C. Corynebacterium parvum

**Core Concept:** Corynebacterium is a genus of Gram-positive, aerobic, rod-shaped bacteria belonging to the family Corynebacteriaceae. Corynebacteria are commonly found in human skin and mucous membranes. Non-diphtheria corynebacteria are those species that do not cause diphtheria.

**Why the Correct Answer is Right:** Corynebacterium parvum is a non-pathogenic, non-diphtheria corynebacterium known for its immunomodulatory properties. It stimulates the immune system by enhancing phagocytosis, increasing neutrophil activity, and promoting the release of cytokines from macrophages and lymphocytes. This leads to a heightened immune response, making it useful in enhancing the effectiveness of cancer immunotherapy and promoting tissue regeneration.

**Why Each Wrong Option is Incorrect:**

A. Corynebacterium glutamicum is a non-pathogenic bacterium used for industrial purposes, such as producing certain amino acids and enzymes. It does not possess immunomodulatory properties, making it an incorrect answer.

B. Corynebacterium diptheriae is the causative agent of diphtheria, a severe respiratory illness. It is a pathogenic bacterium and not suitable for immunomodulation.

C. Corynebacterium parvum is the correct answer, as mentioned above, and possesses immunomodulatory properties, making it the suitable option for this question.

D. Propionibacterium acnes is a Gram-positive, anaerobic bacterium that resides in human skin pores and contributes to skin infections. It is not known for its immunomodulatory properties, rendering it an incorrect answer.

**Clinical Pearl:** Corynebacterium parvum is an essential component in cancer immunotherapy, enhancing the immune response against cancer cells and improving the effectiveness of the therapy. Its application in regenerative medicine and tissue engineering is also being explored. This highlights the importance of understanding the correct answer and knowing the differences between the various species within the Corynebacterium genus.