Regarding the microbiology and laboratory diagnosis of Neisseria gonorrhoeae and Chlamydia trachomatis, all of the following statements are correct EXCEPT:

Explanation

## Microbiology and Diagnosis of Gonorrhea and Chlamydia ### Correct Statements **Key Point:** Neisseria gonorrhoeae is a gram-negative diplococcus with kidney-bean morphology that grows on selective media (Thayer-Martin, Modified Thayer-Martin) containing antibiotics (vancomycin, colistin, nystatin, amphotericin B) to suppress normal flora [cite:Park 26e Ch 26]. **Key Point:** Nucleic acid amplification tests (NAATs) — including PCR, TMA, and SDA — are the gold standard for diagnosis of both gonorrhea and chlamydia, with sensitivity >95% and specificity >99% on urethral, cervical, and urine specimens [cite:Harrison 21e Ch 137]. **Key Point:** Neisseria gonorrhoeae produces oxidase-positive colonies (purple-black color with oxidase reagent), a key identification feature that distinguishes it from other Neisseria species and gram-negative diplococci [cite:Robbins 10e Ch 8]. ### Why Option 1 (Chlamydia on Standard Blood Agar) Is Wrong **High-Yield:** Chlamydia trachomatis is an obligate intracellular bacterium that **cannot** be cultured on standard blood agar or routine bacterial media. It requires cell culture (HeLa cells, McCoy cells, or L-929 cells) or molecular methods (NAATs) for diagnosis. It is not a typical bacterium and lacks peptidoglycan in its cell wall, making it resistant to beta-lactam antibiotics and unable to grow on conventional agar plates [cite:Harrison 21e Ch 137]. **Clinical Pearl:** In clinical practice, culture of Chlamydia is rarely performed; NAATs are preferred because they are more sensitive, faster, and do not require viable organisms. ### Comparison Table: Gonorrhea vs. Chlamydia | Feature | N. gonorrhoeae | C. trachomatis | | --- | --- | --- | | **Gram stain** | Gram-negative diplococcus | Cannot be Gram-stained reliably | | **Culture medium** | Thayer-Martin (selective) | Cell culture or NAATs only | | **Oxidase test** | Positive (purple) | Not applicable | | **Diagnosis** | Culture, NAATs, Gram stain (urethral) | NAATs (gold standard), cell culture (research) | | **Cell wall** | Contains peptidoglycan | Lacks peptidoglycan | **Warning:** Do not confuse culture capability — gonorrhea CAN be cultured on selective media; chlamydia CANNOT be cultured on routine media and requires either cell culture or molecular testing.