Pseudomonas aeruginosa vs Stenotrophomonas maltophilia
How to tell Pseudomonas aeruginosa and Stenotrophomonas maltophilia apart when a board question makes them look alike.
Pseudomonas is oxidase-positive blue-green fruity water/burn/CF pathogen; Stenotrophomonas is broad-antibiotic ICU nonfermenter classically treated with TMP-SMX.
Side by side
Pseudomonas is oxidase-positive non-lactose-fermenting gram-negative rod with blue-green pigment, fruity odor, biofilms, water exposure, burns, CF, neutropenia, and ecthyma gangrenosum.
Stenotrophomonas is a nonfermenting gram-negative rod causing opportunistic hospital infections, especially pneumonia or bacteremia after broad-spectrum antibiotics, ventilators, catheters, or immunosuppression.
Pseudomonas virulence includes exotoxin A, elastases, pyocyanin, biofilm formation, and multidrug resistance.
Stenotrophomonas has intrinsic resistance to many beta-lactams and carbapenems; trimethoprim-sulfamethoxazole is a classic treatment anchor.
Oxidase positivity, pyocyanin/pyoverdine pigment, grape-like/fruity odor, growth in water, and susceptibility to antipseudomonal agents support Pseudomonas.
Carbapenem exposure, ICU pneumonia, catheter bacteremia, nonfermenter ID, and TMP-SMX susceptibility support Stenotrophomonas.
The trap
Both are nonfermenting hospital gram-negative rods, so pigment/oxidase/exposure and antibiotic history separate them.
The repair move
For nonfermenting gram-negative rods, use oxidase, pigment, exposure, and antibiotic history.
Try a free question
CoreA burn patient develops sepsis with green-blue wound drainage, fruity odor, and oxidase-positive non-lactose-fermenting gram-negative rods. Which organism is most likely?
Show answer and explanation
Answer: A. Pseudomonas aeruginosa. Burn infection with blue-green pigment, fruity odor, oxidase positivity, and nonfermenting gram-negative rods supports Pseudomonas.
Why the other choices are tempting
- B. Stenotrophomonas is an opportunistic nonfermenter often after broad-spectrum antibiotics and classically treated with TMP-SMX.
- C. E. coli is a lactose-fermenting Enterobacterales organism.
- D. Klebsiella is a mucoid lactose-fermenting rod.
- E. Bacteroides is an anaerobe.
Flashcards
Tap a card to flip it.
What pigment clue supports Pseudomonas?
Blue-green pigment from pyocyanin/pyoverdine supports Pseudomonas.
What odor clue supports Pseudomonas?
Fruity or grape-like odor supports Pseudomonas.
Quick answers
What is the fastest way to tell Pseudomonas aeruginosa from Stenotrophomonas maltophilia?
Pseudomonas is oxidase-positive blue-green fruity water/burn/CF pathogen; Stenotrophomonas is broad-antibiotic ICU nonfermenter classically treated with TMP-SMX.
What is the key clue for Pseudomonas aeruginosa?
Pseudomonas is oxidase-positive non-lactose-fermenting gram-negative rod with blue-green pigment, fruity odor, biofilms, water exposure, burns, CF, neutropenia, and ecthyma gangrenosum.
What is the key clue for Stenotrophomonas maltophilia?
Stenotrophomonas is a nonfermenting gram-negative rod causing opportunistic hospital infections, especially pneumonia or bacteremia after broad-spectrum antibiotics, ventilators, catheters, or immunosuppression.
What is the common trap with Pseudomonas aeruginosa vs Stenotrophomonas maltophilia?
Both are nonfermenting hospital gram-negative rods, so pigment/oxidase/exposure and antibiotic history separate them.