[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/) › Stenotrophomonas maltophilia

# Stenotrophomonas maltophilia

- Bacterium

## Gram-negative?

Thin wall with an outer membrane: stains pink.

## Contact?

Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

- Exam priority: medium

A water bacterium that infects very sick hospital patients and resists most antibiotics, including carbapenems.

Updated Nov 13, 2026

Also called: Steno

## Quick facts

**Type**
Bacterium · [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

**Gram / shape**
Gram-negative · Straight rod

**Spread**
Hospital water

**Causes**
Hospital-acquired · Chronic airway colonisation

**Treatment**
Trimethoprim-sulfamethoxazole is the first-line drug

On this page

- The basics Key points
- At a glance
- Morphology
- Transmission
- Memory aid
- What the colours mean

- Clinical Virulence factors
- Diseases it causes
- Clinical picture
- Diagnosis

- Treatment Treatment
- Prevention

- Study Test yourself

- Connections Connections

## Key points

- Non-fermenting Gram-negative rod in the ICU that grows during carbapenem treatment: Stenotrophomonas.
- Intrinsic resistance to carbapenems (L1 metallo-beta-lactamase) and aminoglycosides.
- Drug of choice: trimethoprim-sulfamethoxazole.
- Risk: ventilation, central lines, cancer, neutropenia, cystic fibrosis.

## At a glance

**Gram**
Gram-negative

**Shape**
Straight rod

**Oxygen**
Obligate aerobe; does not ferment glucose

**Family**
Lysobacteraceae (formerly Xanthomonadaceae)

## Morphology

- Motile Gram-negative rod with polar flagella
- Usually oxidase-negative, unlike Pseudomonas aeruginosa
- Forms biofilm on plastic, glass and catheters

## Transmission

- Hospital water: taps, sink drains, ice machines, nebulisers and respiratory equipment
- Colonised devices such as central lines and endotracheal tubes
- Hands of health workers can carry it between patients

**Reservoir:** Water, soil and plant roots; moist hospital surfaces

### Isolation precautions

What the care team adds to standard precautions.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

## Virulence factors

- Biofilm on catheters and airway tissue protects it from drugs and immune cells
- L1 metallo-beta-lactamase destroys carbapenems; L2 cephalosporinase adds resistance to cephalosporins
- Efflux pumps and low membrane permeability give intrinsic multidrug resistance, including to aminoglycosides

## Diseases it causes

- Hospital-acquired and ventilator-associated pneumonia [Hospital-acquired and ventilator-associated pneumonia →](https://durgical.com/en/conditions/hospital-acquired-and-ventilator-associated-pneumonia/)
- Catheter-related bloodstream infection and other device infections [Healthcare-associated infections (CLABSI, CAUTI, VAP) →](https://durgical.com/en/conditions/healthcare-associated-infections/)
- Chronic airway colonisation in cystic fibrosis [Cystic fibrosis →](https://durgical.com/en/conditions/cystic-fibrosis/)
- Severe, sometimes haemorrhagic pneumonia in patients with neutropenia or blood cancers [Febrile neutropenia →](https://durgical.com/en/conditions/febrile-neutropenia/)
- A typical multidrug-resistant hospital pathogen [MRSA and other multidrug-resistant organism infections →](https://durgical.com/en/conditions/mrsa-and-other-multidrug-resistant-organism-infections/)

## Clinical picture

- Typical patient: ICU stay, mechanical ventilation, central line, cancer and prior broad-spectrum antibiotics
- Often appears as a breakthrough infection during carbapenem therapy
- Sputum isolates often reflect colonisation; judge by the clinical picture

## Diagnosis

- Grows on standard media; non-fermenting, usually oxidase-negative Gram-negative rod
- Identification by MALDI-TOF mass spectrometry
- Susceptibility testing is essential; separate infection from colonisation

## Treatment

Trimethoprim-sulfamethoxazole is the first-line drug; levofloxacin and minocycline are alternatives, and cefiderocol or ceftazidime-avibactam combined with aztreonam are reserved for highly resistant isolates. It is intrinsically resistant to carbapenems and aminoglycosides; remove infected catheters.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Sulfamethoxazole + trimethoprim (co-trimoxazole)](https://durgical.com/en/pharmacology/sulfamethoxazole-trimethoprim/)
- [Levofloxacin](https://durgical.com/en/pharmacology/levofloxacin/)
- [Minocycline](https://durgical.com/en/pharmacology/minocycline/)
- [Cefiderocol](https://durgical.com/en/pharmacology/cefiderocol/)
- [Ceftazidime + avibactam](https://durgical.com/en/pharmacology/ceftazidime-avibactam/)
- [Aztreonam](https://durgical.com/en/pharmacology/aztreonam/)

## Prevention

- Hand hygiene and contact precautions when the isolate is multidrug-resistant
- Water-safety plans for taps, sinks and respiratory equipment
- Careful central-line care and early removal
- Antimicrobial stewardship: carbapenem use selects for it

## Memory aid

Steno «eats» carbapenems for breakfast with its L1 enzyme; the old sulfa pair (trimethoprim-sulfamethoxazole) is what still stops it.

## Test yourself

Think of the answer, then tap the question to see it.

## Which first-line drug is used for Stenotrophomonas maltophilia infection?

Trimethoprim-sulfamethoxazole.

## Why does Stenotrophomonas often appear in patients already receiving carbapenems?

Its chromosomal L1 metallo-beta-lactamase destroys carbapenems, so carbapenem use selects for it.

## Which hospital reservoirs are linked to Stenotrophomonas?

Water sources such as taps, sink drains and ice machines, and respiratory or intravascular devices.

## Which simple test helps separate Stenotrophomonas from Pseudomonas aeruginosa?

The oxidase test: Stenotrophomonas is usually oxidase-negative, Pseudomonas oxidase-positive.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/stenotrophomonas-maltophilia/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

**Contact**
Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.

**Droplet**
Surgical mask within about a metre; single room.

**Airborne**
N95 respirator and a negative-pressure room.

## Connections

## Related 4

- [Pseudomonas aeruginosa](https://durgical.com/en/microbiology/pseudomonas-aeruginosa/)
- [Acinetobacter baumannii](https://durgical.com/en/microbiology/acinetobacter-baumannii/)
- [Burkholderia cepacia complex and Burkholderia pseudomallei](https://durgical.com/en/microbiology/burkholderia-cepacia-complex-and-burkholderia-pseudomallei/)
- [Other non-fermenting Gram-negative rods](https://durgical.com/en/microbiology/other-non-fermenting-gram-negative-rods/)

## Related conditions 5

- [Hospital-acquired and ventilator-associated pneumonia](https://durgical.com/en/conditions/hospital-acquired-and-ventilator-associated-pneumonia/)
- [Healthcare-associated infections (CLABSI, CAUTI, VAP)](https://durgical.com/en/conditions/healthcare-associated-infections/)
- [Cystic fibrosis](https://durgical.com/en/conditions/cystic-fibrosis/)
- [Febrile neutropenia](https://durgical.com/en/conditions/febrile-neutropenia/)
- [MRSA and other multidrug-resistant organism infections](https://durgical.com/en/conditions/mrsa-and-other-multidrug-resistant-organism-infections/)

[← Back to the group: Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Stenotrophomonas maltophilia: an Emerging Global Opportunistic Pathogen](https://pmc.ncbi.nlm.nih.gov/articles/PMC3255966/) (Clinical Microbiology Reviews (ASM), 2012); [Antimicrobial Treatment Strategies for Stenotrophomonas maltophilia: A Focus on Novel Therapies](https://pmc.ncbi.nlm.nih.gov/articles/PMC8532924/) (Antibiotics (MDPI), 2021).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/stenotrophomonas-maltophilia/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/stenotrophomonas-maltophilia/