Treatment of Serratia Infections with Suspected Resistance to Piperacillin-Tazobactam
For Serratia infections with suspected resistance to piperacillin-tazobactam, carbapenems (particularly meropenem) are the recommended first-line treatment option due to their reliable efficacy and low resistance rates.
First-Line Treatment Options
Carbapenems
Meropenem: 1g IV every 8 hours 1
- Preferred carbapenem for severe Serratia infections
- Extended infusion time (>3 hours) recommended for optimal efficacy
- Strong activity against AmpC-producing organisms like Serratia
Ertapenem: 1g IV daily 2
- Appropriate for less severe infections or outpatient therapy
- Carbapenem-sparing approach to reserve meropenem for more critical cases
- Not active against Pseudomonas (not a concern for Serratia infections)
Second-Line Treatment Options (Based on Susceptibility)
Cephalosporins
Cefotaxime: 2g IV every 8 hours 3
- Low resistance rates reported in Serratia isolates (0.6%)
- Consider for non-severe infections if susceptibility confirmed
Ceftriaxone: 1-2g IV daily 4
- Effective option if susceptibility confirmed
- Higher resistance rates compared to cefotaxime (22.7% vs 0.6%)
Aminoglycosides
- Gentamicin: 5-7.5 mg/kg IV daily 3
- Very low resistance rates reported in Serratia isolates (0.6%)
- Consider for UTIs or as part of combination therapy
- Monitor renal function and drug levels
Fluoroquinolones
- Levofloxacin: 750 mg IV/PO daily 1, 4
- Consider if susceptibility confirmed
- Good option for step-down therapy
Treatment Algorithm
Initial Assessment:
- Determine infection severity (mild, moderate, severe/septic)
- Collect appropriate cultures before starting antibiotics
- Review patient's risk factors for multidrug resistance
Empiric Therapy Selection:
- Severe infection/sepsis: Meropenem 1g IV q8h
- Moderate infection: Ertapenem 1g IV daily or meropenem if concern for concurrent Pseudomonas
- Mild infection: Based on susceptibility - consider cefotaxime, gentamicin, or fluoroquinolones if susceptible
Targeted Therapy (After Susceptibility Results):
- Continue carbapenem if resistant to other options
- De-escalate to narrower spectrum agent if susceptible (cefotaxime, gentamicin, or fluoroquinolone)
Treatment Duration:
- Bloodstream infections: 10-14 days
- Pneumonia: 7-14 days
- UTI: 7-10 days (uncomplicated), 10-14 days (complicated)
- Skin/soft tissue: 7-14 days
Important Considerations
Resistance Mechanisms
Serratia marcescens possesses chromosomal AmpC β-lactamases that can be induced during treatment with certain β-lactams, including piperacillin-tazobactam 5. This inducible resistance mechanism explains why piperacillin-tazobactam may fail despite initial in vitro susceptibility.
Clinical Evidence
The MERINO-2 trial demonstrated higher rates of microbiological failure with piperacillin-tazobactam compared to meropenem (13% vs 0%) for bloodstream infections caused by AmpC-producing organisms including Serratia 5. This supports the recommendation for carbapenem therapy.
Antimicrobial Stewardship
- Reserve broader-spectrum carbapenems (meropenem) for severe infections
- Use ertapenem when possible to spare anti-pseudomonal carbapenems
- De-escalate therapy based on susceptibility results when clinically appropriate
Special Situations
Peritoneal Dialysis-Related Peritonitis
For Serratia peritonitis in peritoneal dialysis patients, catheter removal may be necessary for clinical cure. Piperacillin-tazobactam has shown poor outcomes despite in vitro susceptibility 6.
Neutropenic Fever
For patients with neutropenic fever and suspected Serratia infection, combination therapy with an anti-pseudomonal β-lactam plus an aminoglycoside may be considered initially, with de-escalation once susceptibility results are available 1.
Pediatric Considerations
Dosing adjustments are required for pediatric patients. Meropenem dosing for children is 20-40 mg/kg/dose IV every 8 hours (maximum 2g per dose) 1.