In an otherwise healthy adult with an uncomplicated Enterococcus faecalis urinary tract infection (25‑50 ×10³ CFU/mL) susceptible to nitrofurantoin, what is the appropriate antibiotic regimen and follow‑up?

Appropriate Antibiotic Regimen for Uncomplicated Enterococcus faecalis UTI Susceptible to Nitrofurantoin

Nitrofurantoin 100 mg orally twice daily for 5 days is the recommended first‑line therapy for this uncomplicated Enterococcus faecalis urinary tract infection, achieving approximately 88–93 % clinical cure with excellent activity against enterococci. 1

Rationale for Nitrofurantoin Selection

• Nitrofurantoin demonstrates 80–88 % susceptibility against Enterococcus faecalis isolates, including vancomycin‑resistant strains, making it highly effective for enterococcal UTIs. 2, 3
• The drug retains antimicrobial efficacy against enterococci despite decades of use, with in‑vitro susceptibility rates of 88 % in large surveillance studies. 3
• Nitrofurantoin is specifically FDA‑approved for treatment of UTI caused by E. faecalis and maintains good in‑vitro activity against vancomycin‑resistant enterococci (VRE). 4
• The 5‑day regimen balances optimal efficacy with minimal adverse effects and is the standard duration recommended by the Infectious Diseases Society of America for uncomplicated cystitis. 5

Alternative First‑Line Option

• Fosfomycin 3 g as a single oral dose is an acceptable alternative, as it is FDA‑approved for UTI caused by E. faecalis and shows promising results in retrospective studies of uncomplicated enterococcal UTIs. 4
• Fosfomycin provides the convenience of single‑dose administration while maintaining therapeutic urinary concentrations for 24–48 hours. 1

Penicillin‑Based Therapy (When Susceptibility Confirmed)

• Amoxicillin 500 mg orally every 8 hours for 5–7 days can be used when the isolate is confirmed susceptible to penicillin, as the culture report indicates. 4
• High urinary concentrations of ampicillin or amoxicillin may overcome elevated MICs in ampicillin‑resistant VRE and achieve bactericidal activity in urinary tract infections. 4
• One retrospective study reported 88.1 % clinical eradication and 86 % microbiological eradication in patients with UTI due to ampicillin‑resistant VRE treated with ampicillin, suggesting efficacy even when in‑vitro resistance is present. 4

Reserve Agents (Second‑Line Options)

• Fluoroquinolones (levofloxacin or ciprofloxacin) should be reserved for treatment failures or when first‑line agents are contraindicated, as ciprofloxacin resistance in E. faecalis from complicated UTIs approaches 47 % in some regions. 6, 7
• The culture shows susceptibility to both ciprofloxacin and levofloxacin, but these agents should not be used empirically due to rising resistance and serious adverse effects. 6
• Parenteral agents (daptomycin, linezolid, quinupristin‑dalfopristin) are reserved for pyelonephritis or complicated UTIs and are not indicated for this uncomplicated lower‑tract infection. 8

Follow‑Up Recommendations

• Routine post‑treatment urine culture is not required if symptoms resolve completely by the end of therapy. 1
• Obtain urine culture and susceptibility testing if any of the following occur:
  • Symptoms persist after completing the 5‑day course. 1
  • Symptoms recur within 2 weeks of treatment completion. 1
  • Development of fever > 38 °C, flank pain, or costovertebral angle tenderness suggesting upper‑tract involvement. 1

Critical Contraindications and Pitfalls

• Do not use nitrofurantoin if pyelonephritis is suspected (fever, flank pain, systemic symptoms), as the drug does not achieve adequate renal tissue concentrations. 5
• Avoid nitrofurantoin when creatinine clearance is < 30 mL/min/1.73 m² due to reduced efficacy and increased risk of peripheral neuropathy. 5
• Do not treat asymptomatic bacteriuria in non‑pregnant patients, as this promotes resistance without clinical benefit. 8
• Removal of indwelling urinary catheters should be considered if present, as catheter‑associated bacteriuria often resolves without antimicrobial therapy. 8

Colony Count Interpretation

• The culture shows 25,000–50,000 CFU/mL, which is below the traditional 100,000 CFU/mL threshold but is clinically significant in the presence of symptoms. 1
• The laboratory note indicates the specimen was submitted in a sterile cup requiring refrigeration, which may have affected bacterial growth; a urine culture transport device is recommended for future collections. 1

Clinical Decision Algorithm

1. Confirm uncomplicated lower UTI: No fever, flank pain, pregnancy, catheter, or immunosuppression. 1
2. Verify normal renal function (eGFR ≥ 30 mL/min/1.73 m²). 5
3. Prescribe nitrofurantoin 100 mg PO BID for 5 days as first‑line therapy. 5
4. If symptoms persist after 2–3 days, consider switching to amoxicillin 500 mg PO every 8 hours for 5–7 days (given documented penicillin susceptibility). 4
5. If symptoms recur within 2 weeks, obtain repeat urine culture and consider fosfomycin 3 g single dose or a 7‑day course of an alternative agent. 1