MICROBIOLOGY

• Mycobacterial species
• Slow grower (2-6 weeks for positive with liquid media), photochromogen.
  • AFB staining may show beaded characteristics [Fig].
• DNA analysis suggests there may be 5-7 subspecies.
  
  • Subtype I appears to be responsible for most human infection.
  • M. tuberculosis and M. kansasii can occur together: cultures positive for M. kansasii should be incubated for prolonged periods to exclude M. tuberculosis, which grows slightly slower than M. kansasii.
• Reservoir appears to be water (tap water, standing water, saltwater) with likely infection via aerosol.
• No human-to-human or animal-to-human transmission (with the exception of unusual case reports)