What antibiotic (abx) regimen is recommended for a patient with a suspected or confirmed E coli or Enterobacteriales group infection?

Antibiotic Treatment for E. coli and Enterobacteriales Infections

For community-acquired infections of mild-to-moderate severity, use amoxicillin-clavulanate as first-line therapy, reserving fluoroquinolones and third-generation cephalosporins for severe infections or when local resistance patterns demand broader coverage. 1

Community-Acquired Infections

Mild-to-Moderate Severity

• Amoxicillin-clavulanate is the preferred first-line agent for non-severe community-acquired infections caused by E. coli and Enterobacteriales 1
• Alternative regimens include:
  • Cefotaxime or ceftriaxone plus metronidazole (for intra-abdominal sources) 1
  • Ampicillin plus gentamicin plus metronidazole (particularly in children) 1
  • Ciprofloxacin plus metronidazole as second-choice (though fluoroquinolone resistance in E. coli is increasing) 1

Critical caveat: Ampicillin-sulbactam should NOT be used due to high E. coli resistance rates 1

Severe Community-Acquired Infections

• Cefotaxime or ceftriaxone plus metronidazole for severe infections 1
• Piperacillin-tazobactam as an alternative broad-spectrum option 1
• Meropenem reserved for carbapenem-requiring situations 1
• Imipenem-cilastatin, doripenem are additional carbapenem options for high-risk patients 1

Healthcare-Associated Infections

Risk Stratification is Essential

Healthcare-associated infections require broader empiric coverage due to increased likelihood of resistant organisms, particularly ESBL-producing Enterobacteriales 1

Empiric Therapy Based on Local Resistance Patterns

When ESBL prevalence is ≥20%:

• Carbapenems (imipenem-cilastatin, meropenem, or doripenem) are recommended 1
• These should be combined with metronidazole for intra-abdominal sources 1

When ESBL-producing organisms are suspected but prevalence <20%:

• Piperacillin-tazobactam plus metronidazole 1
• Ceftazidime or cefepime plus metronidazole 1
• Note: Cephalosporins should be discouraged for routine use due to selective pressure for ESBL emergence 1

For multidrug-resistant Pseudomonas (>20% ceftazidime resistance):

• Add an aminoglycoside to the regimen 1

Fluoroquinolone Considerations

Fluoroquinolones (ciprofloxacin, levofloxacin) should be used cautiously due to increasing E. coli resistance globally 1, 2

• Review local susceptibility profiles before empiric use 1
• Reserve for patients with beta-lactam allergies 1
• For uncomplicated UTIs, resistance rates may be lower (15.2% for trimethoprim) than surveillance data suggests 3
• Do NOT use if bloody diarrhea is present (risk of hemolytic uremic syndrome with STEC) 2

Urinary Tract Infections Specifically

Uncomplicated Cystitis (E. coli)

• Nitrofurantoin (5-day course) - highly effective with 83-87% sensitivity 4, 5
• Fosfomycin (3g single dose) 4
• Pivmecillinam (5-day course) 4
• Trimethoprim-sulfamethoxazole only if local resistance <20% 4, 3

ESBL-Producing E. coli UTIs

Oral options:

• Nitrofurantoin (83.2% effective) 5
• Mecillinam (87.92% effective against E. coli) 5
• Fosfomycin 4
• Amoxicillin-clavulanate (for ESBL E. coli only, not Klebsiella) 4

Parenteral options:

• Piperacillin-tazobactam (for ESBL E. coli only) 4
• Carbapenems (meropenem, imipenem-cilastatin) - highly effective (95.5-100% sensitivity) 4, 6
• Ceftazidime-avibactam or ceftolozane-tazobactam 4
• Aminoglycosides (amikacin 87-95.5% sensitive) 6

De-escalation Strategy

Narrow therapy once culture results are available - this is critical for antimicrobial stewardship 1

• Tailor antibiotics based on susceptibility testing for Pseudomonas, Proteus, Acinetobacter, Staphylococcus aureus, and predominant Enterobacteriaceae 1
• Reduce spectrum and number of agents when possible 1
• Shorter treatment durations reduce resistance development 7

Key Resistance Patterns to Remember

• E. coli resistance to ampicillin: 85-97% 6
• E. coli resistance to cotrimoxazole: 70-81% 6
• Fluoroquinolone resistance: Variable but increasing globally 1
• ESBL prevalence: Rising worldwide, particularly in healthcare settings 1

Common Pitfalls to Avoid

• Do not use cephalosporins routinely - they drive ESBL selection 1
• Do not use aminoglycosides for routine community-acquired infections in adults due to toxicity 1
• Do not use fluoroquinolones empirically without checking local resistance patterns 1
• Do not use carbapenems unnecessarily - preserve them for true resistant organisms to prevent carbapenem-resistant Enterobacteriales 1
• Avoid antibiotics entirely if enterohemorrhagic E. coli (STEC) is suspected 2