Mycoplasma genitalium Infection

Mycoplasma genitalium is the smallest known free-living bacterium with the smallest known genome, lacking a cell wall (which makes it intrinsically resistant to beta-lactam antibiotics), first identified in 1981 from urethritis patients. It is now recognized as the second most common cause of non-gonococcal urethritis (NGU) after Chlamydia trachomatis (causing 10-35% of NGU cases), and a significant cause of persistent or recurrent urethritis after initial antibiotic therapy. Prevalence in general populations is 1-2%, higher in STI clinic populations (5-15%) and high-risk individuals.

Clinical manifestations include: in men — urethritis with dysuria and discharge, persistent or recurrent NGU after standard treatment, possible epididymitis, proctitis, and balanitis; in women — cervicitis (often asymptomatic), pelvic inflammatory disease (PID), tubal factor infertility, increased risk of preterm birth and spontaneous abortion, and possible association with bacterial vaginosis. Many infections are asymptomatic, contributing to ongoing transmission. Vertical transmission to neonates can cause respiratory and CNS disease.

Diagnosis requires nucleic acid amplification testing (NAAT) of urine, urethral, vaginal, or cervical swabs (culture is impractical due to slow growth and special media requirements). FDA-cleared NAAT assays are now available, often with simultaneous macrolide resistance mutation testing (23S rRNA gene mutations). Treatment has become increasingly challenging: standard azithromycin 1g single dose has 40-60% failure rates due to widespread macrolide resistance; current recommendations include resistance-guided therapy — for macrolide-sensitive: doxycycline 7 days followed by azithromycin 1g then 500mg daily for 3 days; for macrolide-resistant: doxycycline 7 days followed by moxifloxacin 7-10 days; pristinamycin is alternative for resistant cases. Test of cure 3-4 weeks post-treatment is recommended. Sexual partner notification and treatment is essential.