Question

Gram positive bacteria given below are
(A) Actinomycetes
(B) Clostridium
(C) Mycobacterium
(D) Nocardia
Choose the appropriate answer from the options below:

• A. (A), (B) and (D) only
• B. (A), (B) and (C) only
• C. (A), (B), (C) and (D)
• D. (B), (C) and (D) only

Hint:

Remember that high G+C content bacterial lineages (such as Actinomyces, Streptomyces, Mycobacterium, and Nocardia) are all grouped evolutionary within the Gram-positive bacterial branch.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Bacteria are historically classified into Gram-positive and Gram-negative groups based on the chemical and structural properties of their cell walls.
Gram-positive bacteria possess a thick peptidoglycan layer that retains the crystal violet dye during the Gram-staining protocol.

Step 2: Detailed Explanation:
Let us review each of the listed bacteria:
(A) Actinomycetes:
Actinomycetes are filamentous, branching bacteria.
They are phylogenetically classified under the phylum Actinobacteria, which consists of high G+C Gram-positive bacteria.
(B) Clostridium:
Clostridium is a genus of anaerobic, spore-forming, rod-shaped bacteria.
They are classic low G+C Gram-positive bacteria.
(C) Mycobacterium:
Mycobacterium species possess a unique, lipid-rich cell wall containing mycolic acid.
Because of this waxy wall, they do not stain well with a standard Gram stain and require Acid-Fast staining.
However, from a phylogenetic, biochemical, and evolutionary perspective, they are classified as Gram-positive bacteria within the Actinobacteria phylum.
(D) Nocardia:
Nocardia is a genus of weakly acid-fast, catalase-positive, rod-shaped bacteria that form filamentous branches.
They are structurally and phylogenetically Gram-positive.
Since all four groups are Gram-positive, the correct option is (3).

Step 3: Final Answer:
Actinomycetes, Clostridium, Mycobacterium, and Nocardia are all classified as Gram-positive bacteria.
Thus, the correct choice is option 3.