Microbiology & parasitology
M. genitalium


Topic Completed: 29 July 2020

Minor changes: 4 August 2020

Copyright: 2019-2020, PathologyOutlines.com, Inc.

PubMed Search: M. genitalium[TIAB] review[ptyp][TI]

Arthur H. Totten, Ph.D
Sixto M. Leal, Jr., M.D., Ph.D.
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Cite this page: Totten AH, Farr GA, Leal SM. M. genitalium. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/microbiologymgenitalium.html. Accessed October 24th, 2020.
Definition / general
  • Atypical bacterial pathogen, stained poorly by the dyes used in Gram stain due to the absence of a cell wall
  • Causative agent of nongonococcal urethritis in men and cervicovaginal infections in women
  • Taxonomy: class Mollicutes, order Mycoplasmatales, family Mycoplasmataceae
Essential features
  • Etiologic agent of nongonococcal urethritis
  • Requires specialized media conditions and is not visible on Gram stain
  • Rare extraurogenital infections in immunocompromised patients
  • Increasingly antibiotic resistant (> 80% macrolide resistant, ~ 10 - 20% quinolone resistant) and clinical cure rate of tetracyclines < 30% (Clin Infect Dis 2018;66:796)
Epidemiology
  • Emerging sexually transmitted infection with very high resistance rates
  • Leading cause of nongonococcal urethritis in men and cervicovaginal disease (Clin Microbiol Rev 2011;24:498)
  • Predominantly affects sexually active 18 - 30 year olds but found in all age groups (J Clin Microbiol 2019;57:e01125)
  • Sexually transmitted; asymptomatic carriage is common
  • Rare disseminated infections in immunocompromised individuals
  • Common coinfection with HIV and other STIs (Neisseria gonorrhoeae, Trichomonas vaginalis, ~ 20%)
Sites
Pathophysiology
  • Adhesin / attachment to host cell vital for pathogenesis / initiation of infection (Clin Microbiol Rev 2011;24:498)
  • Lacks cell wall, therefore not susceptible to beta lactams
  • Lipoproteins are main immunogens for immunologic responses during infection
  • Macrolide resistance and fluoroquinolone resistance are common (60 - 80% and 11 - 20%, respectively) and are increasing worldwide
Clinical features
  • Slow growth and high resistance development combine to make eradication difficult
Laboratory
  • Does not stain on a Gram stain due to the lack of a cell wall
  • Does not grow on media typically used in clinical microbiology laboratories
  • Laboratory adapted strains form small, colorless, punctate colonies (dissection scope needed) on SP4 agar within 14 - 30 days when cultured aerobically at 37°C when laboratory adapted (Clin Microbiol Rev 2011;24:498)
  • Color change in liquid media due to glucose metabolism (red to yellow) is characteristic
  • PCR testing required to differentiate from other glucose utilizing mycoplasmas
Case reports
Treatment
  • Common treatment with macrolides, quinolones and tetracyclines
  • Clinical cure rate for tetracyclines is low (< 30%) so combinatorial therapy is common
  • Empiric treatment is common but rates of macrolide resistance are high (60 - 80% in some cases) and fluoroquinolone resistance is increasing (11 - 20%)
  • Compassionate care treatment with minocycline or spectinomycin has been reported (J Antimicrob Chemother 2017;72:624)
Clinical images

Contributed by Sixto M. Leal Jr., M.D., Ph.D.

SP4 broth for culture of lab adapted M. genitalium

SP4 agar photo of M. genitalium colonies

Microscopic (histologic) description
  • Not known
  • Organism not detected on H&E; expect an acute inflammatory background
Molecular / cytogenetics description
Differential diagnosis
  • Neisseria gonorrhea:
    • Gram negative diplococci, oxidase positive, NAAT recommended
  • Chlamydia trachomatis:
    • Not identified on Gram stain, Giemsa stain required, NAAT recommended
Board review style question #1
    A man presents to a sexual health clinic with persistent pain during urination despite empiric treatment with 1g azithromycin. Urine culture, Gram stain and first line molecular tests for urethritis are negative. What organism is the most likely culprit?

  1. Chlamydia trachomatis
  2. Mycoplasma genitalium
  3. Mycoplasma pneumoniae
  4. Neisseria gonorrhea
Board review answer #1
B. Mycoplasma genitalium is the most likely pathogen, as other urogenital pathogens such as C. trachomatis and N. gonorrhea have been ruled out by routine testing. M. pneumoniae is a pulmonary pathogen and is not known to cause infection in the urogenital tract.

Reference: M. genitalium

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Board review style question #2
    Mycoplasma genitalium is best visualized by what microbiology laboratory staining procedure?

  1. Gram stain
  2. Hematoxylin and eosin stain
  3. Methylene blue / Gentian violet stain
  4. No stains reliably stain this organism
Board review answer #2
D. No stains reliably identify this organism. M. genitalium utilizes cholesterol in its membrane and does not have a layer of peptidoglycan, outer membrane or cell wall to stain.

Reference: M. genitalium

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