How to treat Staphylococcus cohnii (coagulase-negative staphylococcus) infection in urine?

Treatment of Staphylococcus cohnii in Urine

Staphylococcus cohnii in urine should be treated with a 7-14 day course of antibiotics only when symptomatic urinary tract infection is present, as this coagulase-negative staphylococcus is not considered a clinically relevant urinary isolate in asymptomatic individuals.

Diagnosis Considerations

When evaluating S. cohnii in urine, consider:

• S. cohnii is a coagulase-negative staphylococcus (CoNS) that is typically considered part of normal skin flora 1
• According to IDSA guidelines, CoNS are not considered clinically relevant urine isolates for otherwise healthy individuals 1
• A proper diagnosis of UTI requires both:
  • Positive urine culture with ≥50,000 CFU/mL of a uropathogen
  • Presence of urinary symptoms 1, 2

Treatment Algorithm

1. Asymptomatic bacteriuria with S. cohnii:

   • Do not treat asymptomatic bacteriuria, even with positive cultures 1
   • Exception: Consider treatment before urologic procedures with mucosal trauma 1

2. Symptomatic UTI with S. cohnii:

   • Remove any urinary catheter if present 2
   • Treat with appropriate antibiotics for 7-14 days 1, 2
   • Base antibiotic selection on susceptibility testing due to high resistance rates 3

3. Special considerations:

   • For catheter-associated UTI: 7-day course for prompt symptom resolution, 10-14 days for delayed response 2
   • Consider shorter course (5 days) for mild cases treated with fluoroquinolones 2

Antibiotic Selection

Based on susceptibility patterns reported for S. cohnii 3:

• First-line options (pending susceptibility):

  • Vancomycin (S. cohnii typically susceptible)
  • Linezolid (S. cohnii typically susceptible)

• Second-line options (high resistance reported):

  • Fluoroquinolones
  • Cephalosporins
  • Ampicillin/amoxicillin

• Always adjust therapy based on culture and sensitivity results

Clinical Pearls and Pitfalls

1. Distinguish colonization from infection:

   • S. cohnii is often a contaminant or colonizer rather than a true pathogen
   • Multiple positive cultures with the same organism increase likelihood of true infection 1

2. Consider complications:

   • S. cohnii has been associated with recurrent staghorn stones 4
   • Evaluate for upper tract involvement if symptoms persist

3. Resistance patterns:

   • S. cohnii isolates show high resistance (>66%) to multiple antibiotics including ampicillin, levofloxacin, erythromycin, and ceftriaxone 3
   • Majority of clinical isolates are methicillin-resistant 3
   • Vancomycin and linezolid resistance is rare 3

4. Biofilm formation:

   • About 60% of S. cohnii isolates are weak biofilm producers 3
   • This may contribute to persistence in catheterized patients

Special Populations

1. Catheterized patients:

   • S. cohnii is more commonly isolated from catheterized patients
   • Remove catheter when possible before initiating treatment 2
   • Do not routinely screen for or treat asymptomatic bacteriuria in patients with long-term indwelling catheters 1

2. Patients undergoing urologic procedures:

   • Screen for and treat bacteriuria prior to procedures with mucosal trauma 1
   • Short course (1-2 doses) of targeted antimicrobial therapy is recommended 1

3. Elderly patients:

   • Consider renal function when dosing antibiotics 2
   • Do not treat asymptomatic bacteriuria in elderly patients 1

Remember that while S. cohnii is generally considered a skin commensal, it has been implicated in various infections including bacteremia, endocarditis, and urinary tract infections 5. Treatment should be reserved for symptomatic cases with evidence of true infection rather than colonization or contamination.