Emery Haley, PhD, Scientific Writing Specialist
Proteus mirabilis
Clinical Summary
- P. mirabilis is recognized as a classical, urease-positive, gram-negative, biofilm-forming, motile uropathogen.
- P. mirabilis is primarily associated with complicated and persistent catheter-associated UTIs.
- In symptomatic UTI patients, P. mirabilis:
- Is not a contaminant (is found in catheter-collected urine specimens).
- Is viable (can grow out on culture).
- Is pathogenic (associated with elevated urine biomarkers of infection).
- Reported severe complications of P. mirabilis UTI include catheter encrustation/blockage, bladder or kidney stones, pyelonephritis, bacteremia, urosepsis, and death.
- Multidrug-resistant P. mirabilis is a significant global health threat.
Bacterial Characteristics
Gram-stain
Gram-negative
Morphology
Bacillus
Growth Requirements
Non-fastidious (grows well in standard urine culture conditions)
Facultative anaerobe
Nitrate Reduction
Yes
Urease
Positive
Biofilm Formation
Yes
Pathogenicity
Colonizer or Pathobiont
Clinical Relevance in UTI
P. mirabilis is a urease-positive,[1]gram-negative, biofilm-forming, motile bacillus classically recognized as a uropathogen. P. mirabilis is particularly well-known both for its swarming motility behavior, which is visible on culture plates and for forming crystalline biofilms on indwelling catheters.[2]
P. mirabilis is infamous for forming multidrug-resistant, polymicrobial, biofilms on indwelling urinary catheters, resulting in catheter-associated UTIs (CAUTIs).[3–5] In preclinical studies, P. mirabilis demonstrated synergism with both Enterococcus species and P. stuartii, including increased urease activity, urolithiasis, cell/tissue damage, and bacteremia.[5,6] In contrast, P. mirabilis exhibits antagonism with E. coli and M. morganii.[5]
This organism’s tendency to form biofilms on urinary catheters and to travel up the urinary tract toward the kidney, as well as its intrinsic and acquired resistance to several classes of antibiotics makes this uropathogen particularly challenging to treat.[2,4,7] In a study of older adult males and females with clinically suspected complicated UTI, P. mirabilis was detected in both midstream voided and in-and-out-catheter collected specimens indicating that it was truly present in the bladder, not simply a contaminant picked up during voiding.[8] Furthermore, elevated markers of immune system activation in the urinary tract have been measured from the same clinical urine specimens in which P. mirabilis was detected, indicating that the presence of P. mirabilis was associated with an immune response to urinary tract infection.[9–11]
Although not considered one of the six highest priority “ESKAPE” pathogens, The World Health Organization (WHO) has included this organism in the 2024 Bacterial Priority Pathogens List (BPPL).[12] Reported severe complications of P. mirabilis UTI include catheter encrustation/blockage, bladder or kidney stones, pyelonephritis, bacteremia, urosepsis, and death.[4,13,14]
Together, these findings indicate that P. mirabilis should be seriously considered as a uropathogen and demonstrate the value of detecting this organism, particularly in individuals with indwelling catheters or other risk factors for complicated UTI.
Treatment
Evidence of Efficacy (Checkmarks): Amoxicillin/Clavulanate, Ampicillin, Ampicillin/Sulbactam, Cefaclor, Cefazolin, Cefepime, Ceftazidime, Ceftriaxone, Ciprofloxacin, Gentamicin, Levofloxacin, Meropenem, Piperacillin/Tazobactam, Sulfamethoxazole/Trimethoprim, and Trimethoprim.