What is the recommended treatment for a urine culture positive for Morganella morganii at 99,000 Colony-Forming Units per milliliter (CFU/mL)?

Treatment of Morganella morganii Urinary Tract Infection

For a urine culture positive for Morganella morganii at 99,000 CFU/mL, treatment with trimethoprim-sulfamethoxazole is recommended based on susceptibility testing, or carbapenems if resistance is present.

Diagnosis Confirmation

Before initiating treatment, it's important to confirm whether this represents a true urinary tract infection (UTI) or asymptomatic bacteriuria:

• A colony count of 99,000 CFU/mL (≥50,000 CFU/mL) of a single organism meets the threshold for significant bacteriuria 1
• Presence of pyuria (leukocytes in urine) is essential to distinguish true UTI from asymptomatic bacteriuria 1
• Symptoms of UTI (dysuria, frequency, urgency) should be present to diagnose symptomatic infection 1

Treatment Approach

First-line Treatment Options:

• Trimethoprim-sulfamethoxazole is indicated for urinary tract infections caused by Morganella morganii according to FDA labeling 2
• Treatment duration:
  • 3-5 days for uncomplicated cystitis in women 1
  • 7 days for men 1
  • 7-14 days for complicated UTIs 1

Alternative Options (based on susceptibility):

• Carbapenems are often effective and commonly used for M. morganii infections 3, 4
• Third-generation cephalosporins (such as ceftazidime) in combination with aminoglycosides (like gentamicin or amikacin) 4, 5

Antimicrobial Resistance Considerations

• M. morganii frequently shows resistance to multiple antibiotics, including:
  • Ampicillin and amoxicillin 6
  • Often resistant to nitrofurantoin 3
  • Variable resistance to ciprofloxacin and gentamicin 3
• Always adjust therapy based on antimicrobial susceptibility testing results 1, 4

Special Patient Populations

Asymptomatic Bacteriuria

• Treatment is NOT recommended for asymptomatic bacteriuria in most populations, including:

  • Premenopausal, non-pregnant women 1
  • Diabetic patients 1
  • Elderly individuals 1
  • Patients with indwelling catheters 1

• Treatment IS recommended for asymptomatic bacteriuria in:

  • Pregnant women (3-7 days of therapy) 1
  • Patients undergoing urologic procedures with mucosal trauma 1

Immunocompromised Patients

• M. morganii can cause severe infections in immunocompromised hosts 3, 7
• More aggressive treatment and monitoring may be needed in transplant recipients or other immunocompromised patients 7

Follow-up

• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients 1
• For patients whose symptoms don't resolve by the end of treatment or recur within 2 weeks:
  • Perform urine culture with susceptibility testing 1
  • Consider 7-day treatment with an alternative agent 1

Clinical Pearls

• M. morganii is an opportunistic pathogen that can cause serious infections, especially in hospitalized or immunocompromised patients 3, 4
• The mortality rate for invasive M. morganii infections can be significant (reported at 41% for bacteremia) 3
• Source control is essential when treating complicated UTIs 3
• Consider underlying structural or functional abnormalities of the urinary tract in patients with M. morganii UTIs, especially with recurrent infections 1