MICROBIOLOGY

• Aerobic, fastidious organism; easier to cultivate than M. genitalium.
  • Differs from bacteria due to smaller size, sterols in the membrane and lack of a cell wall.
  • Due to the lack of a cell wall, M. hominis:
    • Is intrinsically resistant to β-lactams
    • Cannot be detected on Gram stain
  • It differs from M. genitalium because it is intrinsically resistant to 14-member macrolides (erythromycin and clarithromycin; see discussion below).
• M. hominis grows on blood or chocolate agar plates and broth cultures.
  • Visible colonies in 2 - 5 days.
  • Colonies are very small (0.2mm) and translucent, so that they can be easily missed. They have a "fried egg" appearance on agar [Fig, denser in the center and less dense in the periphery].
  • Communicate with the micro lab if you suspect Mycoplasma hominis infection so they can use media that favors Mycoplasma hominis growth.
    • M. hominis in blood culture systems appears to be inhibited by the anticoagulant polyanethole sulfonate which can be neutralized by adding gelatin to a 1% concentration in the blood culture medium, but this is not done routinely.