GPR: 2021 - Week 33

From MGH Learn Pathology

Clinical history

A 45yo male with poorly treated HIV and CD4 count of 10cells/mm^3 presented to the ED with a fever and cough productive of yellow sputum. An expectorated sputum was collected. Mycobacterial culture grown at low temperature on a Lowenstein-Jensen slant in the DARK was positive on day 12.


Registered users must be logged in to access the interactive quiz.


M. gordonae
  • Runyon II, slow scotochromogens (= yellow pigment in light or dark)
  • prefers 28-30degC
  • smooth yellow-orange colonies
  • “tap-water bacillus”
  • most likely a contaminant even in immunocompromised patients
  • risk of respiratory specimen contamination higher if expectorated and if the patient had PO fluids within 2 days
  • BUT infection of ventriculoatrial shunt, endocarditis in prosthetic aortic valve, synovitis, and cutaneous lesions of the hand and face have been reported
  • we have a chemiluminescent DNA probe for M. gordonae targeting ribosomal RNA (GEN-PROBE)

other scotochromogens:

  • M. xenopi - respiratory infections in patienst with underlying lung disease (42degC)
  • M. scrofulaceum - scrofula in normal patients (37degC)



M. kansasii

  • Runyon I, slow photochromogens (= yellow pigment only when exposed to light)
  • prefers 37degC
  • colonies are smooth or rough with “wavy edges” on Middlebrook agar
  • prolonged light exposure forms red crystals of beta-carotene
  • natural source unclear unlike many other NTM which are found broadly in the environment
  • second most common cause of NTM lung disease (#1 = MAC)

other photochromogens:

  • M. marinum - “fish tank granuloma” (28degC)



M. avium

  • Runyon III, slow nonchromogenic
  • M. avium complex (MAC) = avium and intracellulare
  • prefers 37degC
  • smooth tan/white colonies
  • found in soil, water, house dust
  • opportunistic pathogen with a clinical picture similar to MTB
  • most common NTM lung infection

Other slow nonchromogenics:

  • M. ulcerans - common worldwide but rare in the US, trauma -> painless subQ nodule -> shallow ulcer, very slow growing (6+ weeks), 28degC



M. abscessus

  • Runyon IV, fast nonchromogenic
  • grows well at 28 and 37degC,
  • smooth or rough, tan/white to grey colonies
  • common soil and water contaminants
  • skin and soft tissue infections, chronic bronchiectatic pulmonary disease similar to MAC

Other fast nonchromogenics:

  • M. chelonae and M. fortuitum group - variety of infections but known for cutaneous/line/wound/injection sites, both prefer 37degC, M. chelonae more frequently drug resistant
Elvina Lawrence
  • Arnow PM, Bakir M, Thompson K, Bova JL. Endemic contamination of clinical specimens by Mycobacterium gordonae. Clin Infect Dis. 2000 Aug;31(2):472-6. PMID: 10987707.
  • Staropoli JF, Branda JA. Cord formation in a clinical isolate of Mycobacterium marinum. J Clin Microbiol. 2008 Aug;46(8):2814-6. PMID: 18579723; PMCID: PMC2519507.
  • Mahon, C. R., Lehman, D. C., & Manuselis, G. (2014). Textbook of diagnostic microbiology (5th ed.). Saunders.

This week's Gross Pathology Roundup was presented by Sarah Mueller MD, PhD on 2021-08-16.