What is the recommended treatment for infectious Morganella morganii?

Treatment of Infectious Morganella morganii

Carbapenems (such as meropenem or imipenem) are the first-line treatment for Morganella morganii infections, with aminoglycosides (particularly gentamicin or amikacin) as effective alternatives or combination agents. 1, 2, 3

Antimicrobial Options for M. morganii

First-Line Treatments

• Carbapenems: Most effective against M. morganii
  • Meropenem (preferred)
  • Imipenem
  • Ertapenem

Second-Line Options

• Aminoglycosides:
  • Gentamicin (most frequently used aminoglycoside for M. morganii)
  • Amikacin (high susceptibility rates)
• Third-generation cephalosporins:
  • Ceftazidime (good susceptibility profile)

Other Options (Based on Susceptibility)

• Fluoroquinolones:
  • Ciprofloxacin (FDA-approved for M. morganii urinary tract infections) 4
  • Note: Resistance to ciprofloxacin has been reported 3
• Beta-lactam/beta-lactamase inhibitor combinations:
  • Piperacillin-tazobactam
  • Ticarcillin-clavulanate

Treatment Algorithm

1. Initial empiric therapy:

   • Carbapenem (meropenem or imipenem) ± aminoglycoside (gentamicin or amikacin)

2. Once susceptibility results available:

   • Tailor therapy based on susceptibility patterns
   • Consider de-escalation to targeted monotherapy if possible

3. For severe infections or immunocompromised patients:

   • Combination therapy with carbapenem plus aminoglycoside is recommended

4. Duration of therapy:

   • Bloodstream infections: 10-14 days
   • Complicated infections (osteomyelitis, prosthetic joint): 4-6 weeks
   • Urinary tract infections: 7-14 days depending on severity

Special Considerations

Resistance Patterns

M. morganii possesses chromosomal AmpC β-lactamases that can be induced during treatment, leading to resistance to many β-lactam antibiotics 2. Therefore:

• Avoid ampicillin, amoxicillin, and first/second-generation cephalosporins
• Be cautious with third-generation cephalosporins as resistance may develop during treatment
• Monitor for development of resistance during therapy

Polymicrobial Infections

M. morganii is often part of polymicrobial infections (58% of cases in one study) 5. In these cases:

• Ensure coverage for all isolated pathogens
• Consider combination therapy with anaerobic coverage (e.g., metronidazole) for intra-abdominal infections

Source Control

Source control measures (drainage of abscesses, removal of infected devices, debridement of necrotic tissue) are critical components of management, particularly for complicated infections 3.

Clinical Outcomes

• Mortality rates range from 8% in general hospital settings 5 to 41% in patients with bacteremia 3
• Risk factors for poor outcomes include:
  • ICU admission
  • Age >65 years
  • Presence of comorbidities
  • Polymicrobial infections, particularly with Klebsiella pneumoniae

Common Pitfalls to Avoid

• Underestimating the virulence of M. morganii, particularly in immunocompromised patients
• Failing to recognize the potential for inducible resistance to β-lactams during therapy
• Not obtaining adequate source control in complicated infections
• Using antibiotics with poor activity against M. morganii (colistin, nitrofurantoin, trimethoprim/sulfamethoxazole) as these often have high resistance rates 3

In summary, carbapenems remain the cornerstone of therapy for M. morganii infections, with aminoglycosides as valuable alternatives or adjunctive agents. Treatment should be guided by susceptibility testing, with careful attention to potential resistance development during therapy.