What is the first-line treatment for a patient with an Escherichia coli (E. coli) infection?

Treatment of E. coli Infections

For pan-sensitive E. coli, use ciprofloxacin as first-line for systemic infections, or ampicillin plus gentamicin for severe infections like endocarditis, avoiding broad-spectrum agents to preserve them for resistant organisms. 1, 2

Treatment Selection Based on Clinical Context

Systemic Infections and Bacteremia

• Ciprofloxacin is the preferred first-line agent for susceptible E. coli systemic infections including bacteremia 1, 2
• For severe systemic infections or endocarditis with susceptible E. coli, use ampicillin 2 g IV every 4 hours plus gentamicin 1.7 mg/kg every 8 hours 1
• Treat bacteremia for 7-14 days 1, 2
• In severe sepsis, initial combination therapy (beta-lactam plus aminoglycoside) may be considered until susceptibilities confirm pan-sensitivity, then de-escalate to monotherapy 1

Urinary Tract Infections

• Aminoglycosides (gentamicin 5-7 mg/kg/day) are appropriate for complicated UTIs 1
• Treat uncomplicated UTI for 3-7 days and complicated UTI for 5-7 days 1, 2

Intra-Abdominal Infections

For non-critically ill patients with community-acquired infections:

• Amoxicillin/clavulanate 1.2-2.2 g every 6 hours 3
• OR Ceftriaxone 2 g every 24 hours plus metronidazole 500 mg every 6 hours 3
• OR Cefotaxime 2 g every 8 hours plus metronidazole 500 mg every 6 hours 3
• For beta-lactam allergy: Ciprofloxacin 400 mg every 8 hours plus metronidazole 500 mg every 6 hours (only if local E. coli susceptibility to quinolones is ≥90%) 3
• Treat for 5-7 days 1, 2

For critically ill patients with community-acquired infections:

• Piperacillin/tazobactam 4.5 g every 6 hours 3, 1, 2
• OR Cefepime 2 g every 8 hours plus metronidazole 500 mg every 6 hours 3

For healthcare-associated intra-abdominal infections (non-critically ill):

• Piperacillin/tazobactam 4.5 g every 6 hours 3
• For higher risk patients (recent antibiotics, nursing home residents, post-operative): Meropenem 1 g every 8 hours plus ampicillin 2 g every 6 hours 3

For healthcare-associated intra-abdominal infections (critically ill):

• Meropenem 1 g every 8 hours 3
• OR Imipenem/cilastatin 1 g every 8 hours 3
• Add vancomycin 25-30 mg/kg loading dose then 15-20 mg/kg every 8 hours for enterococcal coverage 3

Biliary Infections

• For mild community-acquired biliary infections: oral aminopenicillin/beta-lactamase inhibitor 2
• For severe cases: IV piperacillin/tazobactam or third-generation cephalosporins 3, 2
• Anaerobic coverage is NOT needed unless a biliary-enteric anastomosis is present 3
• Discontinue antibiotics within 24 hours after cholecystectomy for acute cholecystitis unless infection extends beyond the gallbladder wall 3

Critical Antimicrobial Stewardship Principles

Avoid unnecessary broad-spectrum agents:

• Do NOT routinely use carbapenems, piperacillin-tazobactam, or fourth-generation cephalosporins for pan-sensitive organisms to preserve these agents for resistant pathogens 1
• Once susceptibilities confirm pan-sensitivity, de-escalate to narrow-spectrum monotherapy for most infections 1

Enterococcal coverage considerations:

• Empiric enterococcal coverage is NOT necessary for community-acquired intra-abdominal E. coli infections 1
• Enterococcal coverage IS recommended for healthcare-associated infections, particularly post-operative infections, immunocompromised patients, or those with prior cephalosporin exposure 3

Quinolone resistance warning:

• Quinolones should NOT be used unless local E. coli susceptibility is ≥90% due to increasing resistance 3
• Review local population susceptibility profiles before prescribing fluoroquinolones 3

Common Pitfalls to Avoid

• Verify actual susceptibility testing to confirm "pan-sensitive" status (susceptible to ampicillin, first-generation cephalosporins, and fluoroquinolones) 1
• Aminoglycosides should NOT be used as monotherapy except for urinary tract infections due to toxicity concerns 1
• Consider the infection source: biliary and intra-abdominal sources may require anaerobic coverage in addition to E. coli coverage 1
• For bloody diarrhea caused by enterohemorrhagic E. coli (EHEC), avoid antibiotics due to increased risk of hemolytic uremic syndrome 4
• Combination therapy (beta-lactam plus aminoglycoside) demonstrates synergy and is particularly important for endocarditis 1