What should I do for a patient with Urinary Tract Infection (UTI) symptoms, who is positive for tet B and tet M, and has been diagnosed with Enterococcus faecalis and Enterococcus faecium?

Treatment of UTI with Enterococcus faecalis and faecium (tet B and tet M positive)

For this patient with UTI symptoms and both E. faecalis and E. faecium isolated with tetracycline resistance genes (tet B and tet M), you should obtain formal antibiotic susceptibility testing immediately and initiate empiric therapy with high-dose amoxicillin 1000 mg orally three times daily if the patient can take oral medications and has uncomplicated cystitis, or ampicillin 2 g IV every 4-6 hours if hospitalized or has complicated UTI/pyelonephritis. 1, 2

Immediate Diagnostic Steps

• Obtain formal susceptibility testing for ampicillin, vancomycin, and high-level aminoglycoside resistance (gentamicin 120 μg and streptomycin 300 μg) to guide definitive therapy 1, 3
• The presence of tet B and tet M genes indicates tetracycline resistance, which is irrelevant since tetracyclines are not first-line agents for enterococcal UTI 3
• Determine if this is E. faecalis-predominant or E. faecium-predominant infection, as E. faecium exhibits significantly higher antibiotic resistance rates and worse outcomes 4

Risk Stratification

This patient has both E. faecalis and E. faecium, which is concerning because:

• E. faecium demonstrates higher rates of ampicillin resistance (68% resistant vs. 4% for E. faecalis) 1, 3
• E. faecium infections are associated with significantly higher mortality (23% vs. 10.1%), higher CRP levels, and longer hospital stays compared to E. faecalis 4
• Only 3% of E. faecalis strains are multidrug-resistant, while E. faecium resistance is substantially higher 1, 5

Empiric Treatment Algorithm

For Uncomplicated Cystitis (Outpatient)

First-line empiric therapy:

• High-dose amoxicillin 1000 mg orally three times daily for 7-14 days 1, 2
• This achieves MICs two to four times lower than penicillin G against enterococci 1, 2

Alternative oral agents if ampicillin resistance is suspected or confirmed:

• Nitrofurantoin 100 mg orally every 6 hours for 7-14 days (effective for both E. faecalis and E. faecium in uncomplicated UTI) 2, 6, 3
• Fosfomycin 3 g orally as a single dose (particularly for E. faecium) 2, 5, 6

For Complicated UTI or Pyelonephritis (Hospitalized)

First-line empiric therapy:

• Ampicillin 2 g IV every 4-6 hours (gold standard for susceptible E. faecalis) 1
• If ampicillin-resistant or severe penicillin allergy: Vancomycin 30 mg/kg/day IV in 2 divided doses (target trough 10-20 μg/mL) 1

For vancomycin-resistant enterococci (VRE) or if VRE suspected:

• Linezolid 600 mg IV/PO every 12 hours is the preferred agent 1, 5, 7
• Linezolid demonstrates 86.4% microbiological cure rate and 81.4% clinical cure rate for enterococcal infections 2
• Treatment duration: minimum 8 weeks for serious VRE infections 1
• A recent multicenter study showed only 2.5% treatment failure rate with linezolid for enterococcal UTI 8

Alternative for VRE if linezolid contraindicated:

• High-dose daptomycin 10-12 mg/kg/day IV plus ampicillin 18-30 g IV daily (for bacteremia or serious infections) 5
• Standard daptomycin doses (6 mg/kg/day) are inadequate for E. faecium 5

Critical Management Considerations

Source Control

• Remove urinary catheter if present (59.3% of enterococcal UTI patients have catheters) 6, 4
• Failure to remove infected devices will result in treatment failure regardless of antibiotic choice 5, 7
• Evaluate for urinary tract obstruction or stones (as these require intervention) 9

Monitoring Requirements

If using linezolid:

• Monitor complete blood counts weekly due to bone marrow suppression risk, particularly with courses >14-21 days 5, 7
• Watch for peripheral neuropathy with prolonged use 2
• Linezolid is bacteriostatic against enterococci, not bactericidal 7

If using daptomycin:

• Monitor CPK levels at least weekly due to skeletal muscle toxicity risk 5
• Obtain repeat cultures if clinical response is inadequate, as daptomycin resistance can develop during therapy 5

If using vancomycin:

• Target trough concentrations of 10-20 μg/mL 10

Common Pitfalls to Avoid

• Never use cephalosporins alone for enterococcal coverage - they have no intrinsic activity against enterococci despite in vitro synergy when combined with ampicillin 1, 2
• Do not prescribe vancomycin empirically when ampicillin/amoxicillin is superior unless there is documented beta-lactam allergy or confirmed resistance 1, 2
• Do not treat asymptomatic bacteriuria with multidrug-resistant Enterococcus 6
• Avoid fluoroquinolones unless susceptibility is confirmed, as resistance is common 6, 3
• Do not use aminoglycosides as monotherapy - they require combination with cell wall-active agents for synergy 10

Definitive Therapy Adjustment

Once susceptibility results return:

If ampicillin-susceptible E. faecalis predominates:

• Continue or switch to amoxicillin 500 mg orally every 8 hours (for uncomplicated UTI) or ampicillin 2 g IV every 4-6 hours (for complicated UTI) 1, 2

If ampicillin-resistant E. faecium predominates:

• Continue linezolid 600 mg every 12 hours for minimum 8 weeks if VRE 1, 5
• Consider nitrofurantoin or fosfomycin for uncomplicated cystitis 2, 5, 6

If vancomycin-susceptible but ampicillin-resistant:

• Vancomycin 30 mg/kg/day IV in 2 divided doses 1, 5