Treatment of Multi-Drug Resistant Morganella morganii UTI
For a urinary tract infection caused by multi-drug resistant Morganella morganii, treatment with a carbapenem (ertapenem or meropenem) is the most appropriate choice based on the susceptibility pattern shown in the urinalysis and culture results.
Interpretation of Urinalysis and Culture Results
The urinalysis shows clear evidence of a urinary tract infection:
- Cloudy urine appearance
- 3+ leukocyte esterase
- Positive nitrite
30 WBCs/hpf
- Many bacteria
The culture confirms Morganella morganii with the following susceptibility pattern:
- Resistant to: amoxicillin/clavulanic acid, ampicillin, ciprofloxacin, nitrofurantoin, tetracycline, trimethoprim/sulfa
- Susceptible to: cefoxitin, ertapenem, meropenem, piperacillin/tazobactam, tobramycin
Treatment Algorithm
First-line Treatment:
- Carbapenem therapy: Ertapenem 1g IV daily or Meropenem 1g IV q8h 1
- Carbapenems show excellent activity against this MDR organism
- Duration: 5-7 days for complicated UTI 1
Alternative Options (if carbapenems contraindicated):
- Piperacillin/tazobactam: 3.375-4.5g IV q6h 1
- Tobramycin: 5-7 mg/kg/day IV once daily 1
- Aminoglycosides are particularly effective for UTIs due to high urinary concentrations
- Monitor renal function closely
Rationale for Recommendation
The 2022 guidelines for treatment of infections due to multidrug-resistant organisms strongly recommend carbapenems as first-line therapy for complicated UTIs caused by resistant Enterobacterales 1. This recommendation is supported by the susceptibility pattern of the isolate, which shows sensitivity to ertapenem and meropenem.
Multiple studies have demonstrated that M. morganii frequently exhibits resistance to multiple antibiotics, including ampicillin, amoxicillin, first-generation cephalosporins, and many others 2, 3. A 2024 multicenter study found carbapenems to be the most effective treatment for M. morganii infections, with significantly better outcomes compared to other antibiotic classes 4.
Important Clinical Considerations
- Source control: Ensure adequate hydration and urinary flow
- Duration: 5-7 days is typically sufficient for complicated UTI 1
- Monitoring:
- Clinical response should be assessed within 48-72 hours
- Repeat urinalysis may be warranted if symptoms persist
- No need for test of cure if symptoms resolve
Common Pitfalls to Avoid
- Inappropriate empiric therapy: Many standard UTI treatments (nitrofurantoin, trimethoprim/sulfa, fluoroquinolones) are ineffective against this organism
- Prolonged treatment: Extending therapy beyond 7 days rarely provides additional benefit for UTIs and increases risk of resistance
- Failure to recognize AmpC β-lactamase potential: M. morganii can harbor AmpC β-lactamases that may be inducible during therapy with certain β-lactams 3
- Overlooking susceptibility results: Always tailor therapy based on susceptibility testing rather than empiric protocols
The high resistance profile of this M. morganii isolate underscores the importance of obtaining cultures in patients with recurrent or complicated UTIs to guide appropriate antimicrobial selection.