GPR: 2020 - Week 45

GPR Quiz
Answer
DDx1
DDx2
Acknowledgments
Reference(s)

Clinical history

A 72 year-old woman with mixed connective tissue disease (SLE and Sjogren's, on mycophenolate and prednisone) presents with acute abdominal pain and vomiting. Laboratory testing reveals a slight leukocytosis (WBC 14) and eosinophilia. A routine stool culture is performed.

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Strongyloides

Intestinal nematode, 180-380 um long, infects ~30-100 million people worldwide.
Autoinfective life cycle: skin - lungs (via the blood) - intestine - penetrates the intestinal mucosa to re-enter bloodstream.
More severe presentations, higher organism burden in immunosuppressed patients
Tracking phenomenon
- Motile Strongyloides larvae crawl along the agar, dragging normal gut bacteria behind with them.
- Same bacterial hitchhiking occurs in patients, who can present with recurrent gram-negative bacteremia when larvae penetrate gut mucosa.

Salmonella

Salmonella is a gram-negative rod that looks like typical gut flora on a blood agar plate.
Most common food-borne pathogen in the U.S.
Presents most commonly with abdominal pain and fever in adults.
Can be preliminarily identified in stool using the selective and differential Hektoen-Enteric agar, where Salmonella colonies grow as blue-green colonies with black center due to H2S production.

Clostridioides difficile

Obligate anaerobe, would not grow on a routine stool culture.
Important cause of antibiotic-associated pseudomembranous colitis and hospital-acquired diarrhea.
Usually diagnosed with a rapid antigen test, which detects the C. difficile antigen and toxin.
In rare cases when it’s cultured, it can be identified grossly by its very strong horsebarn-like smell and unique greenish/chartreuse fluorescence under UV light.

Denise Bernier and the Microbiology Technologists
George Eng, MD, PhD (C. difficile image)
Will Rothwell, MD, PhD (Salmonella image)

Panosian KJ, Marone P, and Edberg SC. “Elucidation of Strongyloides stercoralis by Bacterial-Colony Displacement.” Journal of Clinical Microbiology, 1986.

This week's Gross Pathology Roundup was presented by Melis Anahtar, MD, PhD on Mon, Nov 02, 2020.