**Core Concept**
Chlamydia is a sexually transmitted bacterium that requires a living cell for its replication, making it challenging to isolate from clinical specimens. The isolation of Chlamydia typically involves cell culture techniques that support the growth of this obligate intracellular pathogen.

**Why the Correct Answer is Right**
The correct method of isolation of Chlamydia involves the use of cell culture techniques such as HeLa cells, McCoy cells, or Hep-2 cells. These cells provide the necessary environment for Chlamydia to replicate. Another method of isolation is the use of antigen detection assays, such as enzyme immunoassay (EIA) or direct fluorescent antibody (DFA) tests. These tests detect the presence of Chlamydia antigens in clinical specimens.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a method of isolation of Chlamydia from clinical specimens. Chlamydia isolation using cell culture techniques is a common method used in clinical laboratories.

**Option B:** This option is incorrect because it is also a method of isolation of Chlamydia from clinical specimens. Antigen detection assays, such as EIA or DFA tests, are commonly used to detect Chlamydia antigens in clinical specimens.

**Option C:** This option is incorrect because it is not a method of isolation of Chlamydia from clinical specimens. Antibiotic susceptibility testing is a method used to determine the effectiveness of antibiotics against a particular bacterial pathogen.

**Clinical Pearl / High-Yield Fact**
Chlamydia is an obligate intracellular pathogen, requiring a living cell for its replication. This unique characteristic makes cell culture techniques essential for its isolation from clinical specimens.

**Correct Answer:** C. Antibiotic susceptibility testing