100. Which one of the following organisms is NOT an obligate intracellular parasite and, therefore,
can grow on bacteriological media?
A. Mycoplasma
B. Chlamydia
C. Rickettsia
D. Adenovirus

Detailed Explanation:

Understanding whether a microorganism is an obligate intracellular parasite is essential for microbiology and infectious disease studies. Obligate intracellular parasites can only reproduce inside the host cells and cannot grow on standard bacteriological media. These organisms rely on the host’s cellular machinery for replication and survival.

Let’s evaluate the organisms mentioned:

1. Mycoplasma

• Not an obligate intracellular parasite

• Unique because it lacks a cell wall, making it naturally resistant to antibiotics like penicillin.

• Despite its minimal genome, Mycoplasma can grow on specialized artificial media, making it an exception among other tiny pathogens.

2. Chlamydia

• Obligate intracellular parasite

• Requires host ATP and cellular machinery to survive and replicate.

• Cannot grow on standard bacteriological media.

3. Rickettsia

• Also an obligate intracellular parasite

• Lives and multiplies within host cells, especially endothelial cells.

• Requires host nutrients and cannot survive or grow on artificial media.

4. Adenovirus

• Not a bacterium, but a virus, and all viruses are obligate intracellular parasites by nature.

• Requires host cells to replicate since they lack metabolic machinery.

Correct Answer:

A. Mycoplasma

It stands out as the only organism in the list that is not an obligate intracellular parasite and can be cultured on specialized bacteriological media, making it significant for diagnostic microbiology and antimicrobial research.