What is the preferred treatment for an elderly male patient with a urinary tract infection (UTI) caused by Morganella morganii, which has potential resistance to trimethoprim (TMP) and sulfamethoxazole (SMX), and a history of benign prostatic hyperplasia (BPH), presenting with chills but no fever?

Treatment of Morganella morganii UTI with Potential TMP-SMX Resistance in Elderly Male with BPH

This patient requires immediate empiric parenteral antibiotic therapy with either an aminoglycoside (gentamicin 5 mg/kg daily or amikacin 15 mg/kg daily) combined with ampicillin, or a third-generation cephalosporin (ceftriaxone 1-2g daily or cefotaxime 2g three times daily), followed by culture-directed therapy once susceptibilities are available. 1, 2

Why This is a Complicated UTI Requiring Aggressive Treatment

This case represents a complicated UTI based on multiple factors that mandate a different approach than simple cystitis:

• Male sex automatically classifies this as complicated 1
• Enlarged prostate (BPH) creates anatomic obstruction, a key complicating factor 1
• Chills without documented fever suggest systemic involvement, potentially indicating early pyelonephritis or prostatic involvement 3, 4
• Morganella morganii is an opportunistic pathogen with high resistance potential and requires targeted therapy 5, 2

Immediate Empiric Antibiotic Selection

First-Line Parenteral Options

Aminoglycoside-based regimen (preferred for Morganella morganii):

• Gentamicin 5 mg/kg once daily PLUS ampicillin 1, 2
• OR Amikacin 15 mg/kg once daily 1, 2
• Rationale: Morganella morganii shows high susceptibility to aminoglycosides (gentamicin and amikacin) in systematic reviews, with gentamicin being the most frequently successful antibiotic 2

Alternative cephalosporin regimen:

• Ceftriaxone 2g once daily 1
• OR Ceftazidime (if available), which shows excellent activity against Morganella morganii 2
• Rationale: Third-generation cephalosporins demonstrate good efficacy, though must test for AmpC β-lactamase production 2

Why NOT to Use TMP-SMX or Fluoroquinolones Empirically

• TMP-SMX resistance is documented in Morganella morganii isolates 5, and you already suspect resistance
• Fluoroquinolones should be avoided in elderly patients due to increased risk of tendon rupture, CNS effects, and QT prolongation 3, 6, 7
• Ciprofloxacin resistance is common in Morganella morganii 5

Critical Diagnostic Steps Required Immediately

Obtain urine culture with susceptibility testing before starting antibiotics 3, 7

• This is mandatory given the resistant organism and need for targeted therapy 7
• Culture results will guide definitive antibiotic selection 2

Obtain blood cultures if systemic signs worsen 3

• Chills suggest possible bacteremia, which occurs with Morganella morganii in 41% mortality rate if untreated 5
• Morganella morganii can cause septic shock, particularly in patients with prostatic involvement 4

Assess renal function immediately using Cockcroft-Gault equation 7

• Elderly patients have approximately 40% decline in renal function by age 70 3
• Aminoglycoside dosing requires adjustment based on creatinine clearance 1

Prostatic Involvement Considerations

Given the BPH history and systemic symptoms (chills), prostatic involvement must be considered:

• If prostatitis is suspected, extend treatment duration to 4-6 weeks minimum 8
• Chronic bacterial prostatitis requires prolonged therapy (6-12 weeks) 8
• Once culture results return, consider transition to oral therapy with agents that penetrate prostatic tissue 8

Oral Options After Culture Results (if susceptible):

• Fosfomycin 3g every other day for extended duration if susceptible—case reports show success in chronic prostatitis 9
• Fluoroquinolone only if susceptible and no other options (levofloxacin 750mg daily), despite elderly concerns 8
• Avoid TMP-SMX given suspected resistance 5

Treatment Duration Algorithm

Initial parenteral therapy: 48-72 hours minimum until clinical improvement 3, 7

Total duration depends on infection site:

• Complicated UTI without prostatic involvement: 7-14 days 7
• Acute bacterial prostatitis: 4 weeks 8
• Chronic bacterial prostatitis: 6-12 weeks 8

Monitoring and Follow-Up

Reassess at 48-72 hours for:

• Clinical improvement (resolution of chills, improved voiding symptoms) 3, 7
• Recheck renal function after hydration and antibiotic initiation 3
• Adjust antibiotics based on culture susceptibilities 2

If no improvement by 72 hours:

• Consider imaging (ultrasound or CT) to evaluate for prostatic abscess or urinary obstruction 1
• Broaden coverage or switch to carbapenem (imipenem 0.5g three times daily or meropenem 1g three times daily) 1

Critical Pitfalls to Avoid

• Do not use nitrofurantoin—ineffective against Morganella morganii and contraindicated in potential pyelonephritis/prostatitis 3, 5
• Do not use amoxicillin-clavulanate empirically—not recommended for UTI in elderly and Morganella morganii shows resistance 3, 5
• Do not undertreated duration—male UTIs with BPH require minimum 7-14 days, longer if prostatic involvement 7, 8
• Do not ignore the 15% mortality risk—Morganella morganii carries significant mortality in elderly patients with comorbidities 5