GPR: 2020 - Week 05

From MGH Learn Pathology

Clinical history

A 34 year-old sexually active woman presents with urinary frequency and dysuria. Urinalysis showed a pH of 7.6 positive, leukocyte esterase, and positive nitrites. “Clean catch” urine was cultured on a Urine Biplate (Tryptic soy agar with 5% sheep blood / MacConkey II agar with MUG).

GPR20-2 -Proteus mirabilis.png

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

GPR20-2 -Proteus mirabilis.png

Proteus mirabilis
  • family Enterobacteriaceae
  • Gram-negative rod, facultative anaerobe, 90% of Proteus infections are P. mirabilis
  • alkaline urine due to high urease expression, associated with kidney stones
  • polysaccharide secretion allows increased motility along surfaces, biofilm formation
  • grey swarming growth on sheep blood, “fishy odor”
  • colorless (non-lactose fermenting), non-swarming colonies on MacConkey agar
  • indole negative (P. vulgaris is indole positive)

GPR20-2 -Pseudomonas aeruginosa.jpg


Pseudomonas aeruginosa

  • family Pseudomonadaceae
  • encapsulated Gram-negative rod, facultative anaerobe
  • frequently seen in cystic fibrosis and burn patients
  • thrives on moist surfaces, creates biofilms
  • non-lactose fermenter on MacConkey, “grape odor”
  • green on solid media due to water soluble pigments pyocyanin and pyoverdin
  • ‘aeruginosa’ from Latin for copper rust

GPR20-2 -E coli O157.png


Escherichia coli

  • family Enterobacteriaceae
  • Gram-negative rod, facultative anaerobe
  • grey, nondescript colonies on sheep blood
  • pink on MacConkey (lactose-fermenter)
  • indole positive and beta-glucuronidase positive (MUG)
  • this isolate was beta-glucuronidase negative and does not ferment sorbitol
  • bright yellow-orange on Hektoen enteric agar => E. coli O157

GPR20-2 -Candida albicans.jpg


Candida albicans

  • Gram-positive yeast +/- pseudohyphae
  • GI flora (40-80% of humans) and opportunistic pathogen, forms biofilms
  • creamy, white colonies with “feet” on sheep blood
  • S. aureus colonies are white and creamy but are (usually) beta-hemolytic and lack feet
  • C. albicans is green on CHROMagar (C. tropicalis = blue, C. krusei = light pink)
Hiep Nguyen

Kay Hogle

John Branda
Jorgensen, James H. Manual of Clinical Microbiology. 11th ed. ASM Press; 2015. Mais, Daniel D. Practical Clinical Pathology. 2nd ed. ASCP Press; 2017.

This week's Gross Pathology Roundup was presented by Sarah Mueller, MD, PhD on Mon, Jan 27, 2020.