Microbiology · MU Sofia

82. Genus Mycoplasma. Ureaplasma urealyticum

Covers the general features of the genus Mycoplasma, including its lack of a cell wall, sterol-containing membrane and resistance to beta-lactams, then its morphology and virulence factors. It goes on to epidemiology, clinical disease caused by M. pneumoniae and by Ureaplasma urealyticum and M. hominis, laboratory diagnosis, treatment and prevention. A summary table of morphology and a table of diagnostic tests are included, along with a list of complications of M. pneumoniae.

Inside: 9 sections · 5 labelled pictures · 2 tables · 14 flashcards · 3 min

Topic 82 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 9 sections, about 324 words (3 min of reading), with 14 flashcards.

In this note

  1. Genus Mycoplasma. Ureaplasma urealyticum
  2. I. General Characteristics
  3. II. Morphology and Structural Features
  4. III. Virulence Factors
  5. IV. Epidemiology
  6. V. Clinical Manifestations
  7. VI. Laboratory Diagnosis
  8. VII. Treatment
  9. VIII. Prevention

I. General Characteristics

  • Smallest free-living bacteria (0.1–0.3 μm).
  • Lack a cell wall: not visible on Gram stain, pleomorphic (variable shape).
  • Triple-layered membrane contains sterols (unusual for bacteria — taken from host).
  • Resistant to β-lactam antibiotics (penicillins, cephalosporins).
  • Facultative anaerobes or aerobes.
  • Fastidious: grow slowly on enriched media with sterols (e.g. SP4 medium).
  • Includes:
  • Mycoplasma pneumoniae – respiratory pathogen.
  • Mycoplasma hominis, Mycoplasma genitalium – urogenital infections.
  • Ureaplasma urealyticum – part of normal flora; causes genital and perinatal infections.

III. Virulence Factors

  • Adhesins: e.g., P1 protein in M. pneumoniae — binds to respiratory epithelium (sialic acid).
  • Hydrogen peroxide production: damages host cell membranes.
  • Ciliostasis: interferes with mucociliary clearance.
  • Urease activity (in Ureaplasma): hydrolyzes urea → ammonia → cytotoxic effects on uroepithelium.
  • Surface antigen variation: immune evasion.
  • Induces autoimmune responses due to antigen mimicry (e.g., cold agglutinins in M. pneumoniae).

IV. Epidemiology

  • Reservoir: Humans — respiratory and genitourinary tract.
  • Transmission:
  • M. pneumoniae: respiratory droplets (crowded environments, schools, military).
  • Ureaplasma / M. hominis: sexual contact, vertical transmission during delivery.
  • Common in young adults and adolescents.
  • Normal flora: Ureaplasma and M. hominis are found in ~40–80% of sexually active women.

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