Proteus mirabilis UTI is Not Sensitive to Macrobid (Nitrofurantoin)
Proteus mirabilis urinary tract infections should not be treated with nitrofurantoin (Macrobid) as this organism demonstrates intrinsic resistance to this antibiotic. 1
Antimicrobial Susceptibility of Proteus mirabilis
- Proteus mirabilis shows extremely poor susceptibility to nitrofurantoin, with studies reporting susceptibility rates as low as 3.2% 1
- This organism is naturally resistant to nitrofurantoin due to its intrinsic characteristics and resistance mechanisms 1
- Nitrofurantoin resistance in P. mirabilis is significantly associated with the presence of multiple virulence genes including hpmA, ureC1, rpoA, atfA, atfC, mrpA, and pm1 1
Recommended Antimicrobial Options for Proteus mirabilis UTI
For uncomplicated UTIs caused by P. mirabilis, the European Association of Urology recommends:
For complicated UTIs involving P. mirabilis, recommended options include:
Epidemiology and Characteristics of Proteus mirabilis in UTIs
- P. mirabilis is one of the common uropathogens found in cultures, particularly in complicated UTIs 2
- It is the third most common bacterium causing complicated UTIs, especially in catheterized patients 1
- P. mirabilis is a urease-producing bacterium that can lead to stone formation in the urinary tract 2
- If persistent growth of P. mirabilis is detected, stone formation in the urinary tract must be excluded 2
Clinical Implications and Management
- Urine culture and susceptibility testing should always be performed when P. mirabilis is suspected 2
- Initial empiric therapy should be tailored based on local resistance patterns and then adjusted according to culture results 2
- Treatment duration for P. mirabilis UTIs generally ranges from 7-14 days (14 days for men when prostatitis cannot be excluded) 2
- Appropriate management of any underlying urological abnormality or complicating factor is mandatory 2
Antibiotic Resistance Patterns
- P. mirabilis shows variable resistance to commonly used antibiotics:
- High resistance to trimethoprim-sulfamethoxazole (up to 80.6% in some regions) 3
- Moderate resistance to amoxicillin-clavulanic acid (57.3%) 3
- Increasing resistance to third-generation cephalosporins (55.3% for ceftazidime) 3
- Relatively low resistance to ciprofloxacin (30.2%) 1
- High resistance to nitrofurantoin (96.8%) 1
Important Clinical Considerations
- Multi-drug resistant (MDR) P. mirabilis isolates are increasingly reported worldwide, particularly among catheterized patients 3
- Extended-spectrum β-lactamase (ESBL) production is becoming more common in P. mirabilis, complicating treatment options 3
- P. mirabilis has a strong capacity to form biofilms, which can make antibiotic therapy more difficult 4
- Local antibiograms should guide empiric therapy choices due to regional variations in resistance patterns 5