Is Morganella morganii urinary tract infection (UTI) only treatable with intravenous (IV) antibiotics?

Treatment of Morganella morganii UTI: Oral vs. IV Antibiotics

Morganella morganii UTIs can be effectively treated with oral antibiotics in many cases, and IV antibiotics are not always required.

Understanding Morganella morganii

Morganella morganii is a gram-negative bacillus that can cause urinary tract infections, particularly in hospitalized patients and those with compromised immune systems. While it presents treatment challenges due to its intrinsic resistance patterns, oral treatment options are available.

Antibiotic Selection for M. morganii UTI

First-line Treatment Options:

• Oral options:
  • Trimethoprim-sulfamethoxazole (TMP-SMX): FDA-approved for UTIs caused by M. morganii 1
  • Ciprofloxacin: 500-750 mg twice daily for 7 days (if local resistance <10%) 2
  • Levofloxacin: 750 mg once daily for 5 days 2

Alternative Options (Based on Susceptibility Testing):

• Oral cephalosporins: Less reliable due to potential AmpC β-lactamase production
• IV options (for severe infections or resistance to oral agents):
  • Carbapenems: First choice for resistant strains 3
  • Aminoglycosides: Particularly amikacin 4
  • Ceftazidime: If susceptible 4

Treatment Algorithm

1. Assess severity and complications:

   • Uncomplicated UTI (no fever, flank pain, or systemic symptoms)
   • Complicated UTI/pyelonephritis (fever, flank pain, systemic symptoms)
   • Presence of urinary obstruction or structural abnormalities

2. Obtain cultures before starting antibiotics

3. Initial treatment selection:

   • For uncomplicated UTI: Start with oral TMP-SMX or fluoroquinolone (if local resistance <10%)
   • For complicated UTI/pyelonephritis:
     • Stable patient: Start with oral fluoroquinolone
     • Unstable patient or suspected resistance: Start with IV therapy (carbapenem or aminoglycoside)

4. Treatment duration:

   • Uncomplicated UTI: 7 days
   • Complicated UTI/pyelonephritis: 10-14 days

Special Considerations

• Resistance patterns: M. morganii commonly shows resistance to ampicillin, amoxicillin, first and second-generation cephalosporins, nitrofurantoin, and colistin 3, 4
• AmpC β-lactamases: M. morganii can produce inducible AmpC β-lactamases that may develop resistance during treatment with certain β-lactams 5
• Combination therapy: Consider combination therapy for severe infections or suspected resistance 4

Important Caveats

• Always obtain cultures and susceptibility testing to guide definitive therapy
• M. morganii has shown increasing resistance to multiple antibiotics, including ciprofloxacin and TMP-SMX in some regions 3
• Source control is critical if there are complicating factors like obstruction
• Consider infectious disease consultation for multidrug-resistant strains

Conclusion

While M. morganii can be challenging to treat due to its resistance patterns, oral antibiotics like TMP-SMX and fluoroquinolones remain effective first-line options for uncomplicated UTIs. IV antibiotics should be reserved for complicated infections, severe presentations, or cases with documented resistance to oral agents.