[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Enterobacterales](https://durgical.com/en/microbiology/groups/enterobacterales/) › Proteus mirabilis

[Microbiology](https://durgical.com/en/microbiology/) · [Enterobacterales](https://durgical.com/en/microbiology/groups/enterobacterales/)

# Proteus mirabilis

- Bacterium
- Gram-negative
- Exam priority: medium

A bacterium that causes urinary infections, especially with catheters, and builds large stones by making urine alkaline.

Updated 2026-11-01

## Key points

- Urease-positive: alkaline urine and staghorn struvite stones.
- Swarming motility over the agar plate.
- Non-lactose fermenter that makes H2S.
- Intrinsically resistant to nitrofurantoin and tetracyclines.
- Catheter-associated urinary infection with a blocked catheter.

## At a glance

**Gram**
Gram-negative

**Shape**
Rod

**Oxygen**
Facultative anaerobe

**Family**
Morganellaceae

**Stain**
Gram: red rods

## Morphology

- Highly motile Gram-negative rod
- Spreads in waves across the whole agar plate (swarming)
- Non-lactose fermenter; makes H2S; strongly urease-positive
- Indole-negative (P. vulgaris is indole-positive)

## Transmission

- Endogenous infection from gut flora
- Climbs the urethra, especially in people with long-term urinary catheters

**Reservoir:** Human gut, soil and water

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Urease: splits urea into ammonia, raises urine pH and precipitates struvite (magnesium ammonium phosphate) stones
- Crystalline biofilm that blocks catheters
- Flagella and swarming motility: ascent up the urinary tract
- Fimbriae, hemolysin and proteases

## Diseases it causes

- Complicated urinary tract infection, mainly catheter-associated [Urinary tract infection (acute cystitis) →](https://durgical.com/en/conditions/urinary-tract-infection/)
- Struvite stones, sometimes staghorn calculi filling the renal pelvis [Kidney stones (urolithiasis) →](https://durgical.com/en/conditions/kidney-stones/)

## Diagnosis

- Alkaline urine pH with struvite ("coffin lid") crystals
- Urine culture: colonies that swarm over the plate, with a typical smell
- Imaging to look for staghorn stones

## Treatment

By antibiogram: usually susceptible to ampicillin, cephalosporins, trimethoprim-sulfamethoxazole and fluoroquinolones. It is intrinsically resistant to nitrofurantoin, tetracyclines and polymyxins. Infected stones are removed, because the bacteria persist inside them.

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

In Pharmacology:

- [Beta-lactams](https://durgical.com/en/pharmacology/classes/beta-lactams/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)

## Prevention

- Avoiding unneeded catheters and changing or removing them on time
- Treatment of recurrent urinary infections

## Memory aid

"Proteus lays the stone": its urease turns urine alkaline and builds a coral reef inside the kidney.

## Test yourself

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

## Which Proteus mirabilis enzyme explains struvite stones?

Urease, which turns urea into ammonia and makes urine alkaline.

## What does Proteus look like on an agar plate?

It spreads in waves over the whole plate because of swarming motility.

## Which cystitis drug does not work against Proteus because of intrinsic resistance?

Nitrofurantoin.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/microbiology/proteus-mirabilis/)

## Related

- [Escherichia coli](https://durgical.com/en/microbiology/escherichia-coli/)
- [Klebsiella pneumoniae](https://durgical.com/en/microbiology/klebsiella-pneumoniae/)

## Related conditions

- [Urinary tract infection (acute cystitis)](https://durgical.com/en/conditions/urinary-tract-infection/)
- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)

## 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.

[← Back to the group: Enterobacterales](https://durgical.com/en/microbiology/groups/enterobacterales/)

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

Sources: [Proteeae Infections](https://www.msdmanuals.com/professional/infectious-diseases/gram-negative-bacilli/proteeae-infections) (MSD Manual Professional Edition, 2024); [Kidney stones](https://medlineplus.gov/ency/article/000458.htm) (MedlinePlus, 2026).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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