Is E. coli susceptible to Zosyn (piperacillin/tazobactam)?

From the Guidelines

Yes, E. coli is generally susceptible to Zosyn (piperacillin/tazobactam), but its effectiveness can be limited by the presence of extended-spectrum beta-lactamase (ESBL)-producing strains.

Key Points to Consider

• Zosyn is a broad-spectrum antibiotic that combines piperacillin, a penicillin-type antibiotic, with tazobactam, a beta-lactamase inhibitor, which helps to overcome resistance in some bacteria, including some strains of E. coli 1.
• The typical adult dosage of Zosyn is 3.375g (3g piperacillin/0.375g tazobactam) administered intravenously every 6 hours, or 4.5g (4g piperacillin/0.5g tazobactam) every 6-8 hours for more severe infections, with dosage adjustments needed for patients with renal impairment.
• However, the use of Zosyn in patients with ESBL-producing E. coli infections is still controversial, as these strains may exhibit resistance to piperacillin/tazobactam 1.
• In cases where E. coli is suspected or confirmed to be an ESBL-producer, alternative antibiotics such as carbapenems or newer agents like ceftolozane/tazobactam or ceftazidime/avibactam may be more effective 1.
• It's crucial to note that antibiotic resistance patterns can vary significantly by region and over time, making local epidemiology and susceptibility testing essential for guiding treatment decisions 1.

Clinical Considerations

• The choice of empiric antibiotic therapy for intra-abdominal infections, where E. coli is a common pathogen, should be based on the clinical condition of the patient, individual risk factors for resistant pathogens, and local resistance epidemiology 1.
• In critically ill patients, timely and effective administration of antibiotics is critical, and the selection of an agent with appropriate penetration to the site of infection, considering the patient's pathophysiological status and the pharmacokinetic properties of the drug, is essential 1.
• Given the potential for resistance and the importance of appropriate antibiotic use to minimize the development of further resistance, susceptibility testing should be performed whenever possible to confirm the effectiveness of Zosyn or any other chosen antibiotic against the specific E. coli isolate 1.

From the FDA Drug Label

Piperacillin and tazobactam for injection, USP is indicated in adults and pediatric patients (2 months of age and older) for the treatment of appendicitis (complicated by rupture or abscess) and peritonitis caused by beta-lactamase producing isolates of Escherichia coli Piperacillin and tazobactam for injection, USP is indicated in adults for the treatment of postpartum endometritis or pelvic inflammatory disease caused by beta-lactamase producing isolates of Escherichia coli. Aerobic bacteria Gram-negative bacteria Escherichia coli

E. coli is covered by Zosyn (piperacillin/tazobactam), as it is indicated for the treatment of infections caused by beta-lactamase producing isolates of Escherichia coli, including intra-abdominal infections and female pelvic infections 2.

• Key points:
  • Zosyn is effective against beta-lactamase producing E. coli
  • It is used to treat various infections, including intra-abdominal and female pelvic infections caused by E. coli
  • The drug label provides specific information on the susceptibility of E. coli to piperacillin/tazobactam 2

From the Research

Susceptibility of E. coli to Zosyn (Piperacillin/Tazobactam)

• E. coli susceptibility to piperacillin/tazobactam has been studied in various research papers 3, 4, 5, 6, 7.
• According to a study published in 2008, piperacillin/tazobactam exhibited good in vitro susceptibility against ESBL-producing E. coli, with 95.8% sensitivity 3.
• Another study from 1998 found that 75% of all isolates, including E. coli, were sensitive to piperacillin/tazobactam 4.
• A French multicentre study in 2010 reported a cumulative susceptibility rate of 90% for piperacillin/tazobactam against E. coli 5.
• The activity of piperacillin/tazobactam against clinical isolates, including E. coli, was also evaluated in a UK study in 1993, which found that tazobactam enhanced the activity of piperacillin against Enterobacteriaceae, including E. coli 6.
• A recent study in 2025 assessed the reliability of various antimicrobial susceptibility testing methods for piperacillin/tazobactam in challenging E. coli isolates, finding that most methods were generally reproducible, but certain isolates may present inconsistent MIC results 7.

Key Findings

• Piperacillin/tazobactam has been shown to be effective against E. coli, including ESBL-producing strains 3, 5.
• The susceptibility of E. coli to piperacillin/tazobactam can vary depending on the testing method and the specific isolate being tested 4, 6, 7.
• Overall, the available evidence suggests that piperacillin/tazobactam is a viable treatment option for E. coli infections, but susceptibility testing should be performed to confirm effectiveness 3, 4, 5, 6, 7.