**Question:** Non gonococcal urethritis is mostly caused by:

A. Chlamydia trachomatis
B. Ureaplasma urealyticum
C. Mycoplasma genitalium
D. Neisseria gonorrhoeae

**Core Concept:** Non-gonococcal urethritis (NGU) is a condition characterized by inflammation of the urethra (the tube that carries urine from the bladder to the outside) caused by various pathogens, primarily bacteria and sexually transmitted infections (STIs). NGU is different from gonococcal urethritis, which is caused by Neisseria gonorrhoeae.

**Why the Correct Answer is Right:** Non-gonococcal urethritis is mainly caused by Chlamydia trachomatis, Ureaplasma urealyticum, and Mycoplasma genitalium. These microorganisms are small, obligate intracellular bacteria that can evade the immune system and cause inflammation in the urethral tissues without causing visible signs of infection.

**Why Each Wrong Option is Incorrect:**

A. Neisseria gonorrhoeae (D) is responsible for gonococcal urethritis, not non-gonococcal urethritis. Gonorrhea is caused by Neisseria gonorrhoeae, which is large and extracellular, leading to more obvious symptoms and signs of urethritis.

B. Unlike N. gonorrhoeae, Chlamydia trachomatis, Ureaplasma urealyticum, and Mycoplasma genitalium are small, obligate intracellular bacteria that can cause inflammation without causing visible signs of infection.

C. While Mycoplasma genitalium can cause NGU, it is less common compared to C. trachomatis and Ureaplasma urealyticum.

**Clinical Pearl:** Understanding the distinction between gonococcal and non-gonococcal urethritis is crucial for proper diagnosis and treatment. NGU is often asymptomatic, making diagnosis challenging. Treatment typically involves a combination of antibiotics targeting Chlamydia, Ureaplasma, and Mycoplasma species.

**Correct Answer:** C. Mycoplasma genitalium

**Why This is the Correct Answer:** Mycoplasma genitalium is a less common cause of non-gonococcal urethritis, often associated with other STIs, or coinfection with Chlamydia trachomatis or Ureaplasma urealyticum. The correct answer is 'C' Mycoplasma genitalium, as it is one of the common causes of non-gonococcal urethritis. Treatment typically involves a combination of antibiotics targeting Chlamydia, Ureaplasma, and Mycoplasma species.