GPR: 2020 - Week 33

From MGH Learn Pathology

Clinical history

A two year-old boy w/ PMH of recurrent respiratory infections presents with 1-wk hx of cough, sputum, fever, and dyspnea. Plating of a BAL specimen on Mueller-Hinton agar resulted in the appearance below.

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P. aeruginosa
  • P. aeruginosa belongs to the fluorescent group of pseudomonas spp. They all produce the diffsubile pigment pyoverdin, a siderophore implicated in virulence and biofilm formation. It has a yellow-green to yellow-brown hue.
  • P. aeruginosa is the only member of the group that also produces the blue pigment pyocyanin.
  • When pyoverdin and pyocyanin are combined the bright (lime/apple) green color of P. aeruginosa is produced.

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P. fluorescens

  • All members of the fluorescent Pseudomonas group fluoresce under short UV-light, due to pyoverdin.
  • Both P. aeruginosa (shown) and P. fluorescens fluoresce and can have green color.
  • They can be differentiated by growth at 42 °C (pos. for P. aeruginosa/ neg. for P. fluorescens).

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P. putida

  • P. putida is also a member of the fluorescent group.
  • It lacks distinct colony morphology (similar to P. fluorescens).
  • It can be differentiated from P. fluorescens by its inability to grow at 4 C or hydrolyze gelatin.
  • Bonus: P. aeruginosa (images shown) besides bright green, can also be red (due to pyorubin; shown) or brown-black (pyomelanin).
  • Primary sites of infection can be colored due to pigment deposition (e.g. green nail syndrome/chromonychia; shown).

  • Dr. John Branda
  • Dr. Melis Anahtar
  • Lisa Desrosiers
Manual of Clinical Microbiology, 11th ed. (2015). ASM Press. Bae, Y., et al. (2014) Green nail syndrome treated with the application of tobramycin eye drop. Ann. Dermatology. PMID: 25143684.

This week's Gross Pathology Roundup was presented by Tasos Gogakos, MD on Mon, Aug 10, 2020.