What does Lactobacillus growth in an otherwise normal culture result mean and how should it be managed?

Lactobacillus in Urine Culture: Interpretation and Management

Lactobacillus growth in an otherwise normal urine culture typically represents vaginal flora contamination and does not require antimicrobial treatment in most cases. This finding should be interpreted in the context of clinical symptoms and urinalysis results.

Clinical Significance of Lactobacillus in Urine

Lactobacillus species are:

• Normal inhabitants of the vaginal flora in women
• Rarely pathogenic organisms
• Usually considered contaminants when found in urine cultures

Key Considerations for Interpretation

1. Urinalysis Results:

   • Presence of pyuria (>250 PMN/mm³) suggests true infection 1
   • Normal urinalysis with Lactobacillus alone typically indicates contamination

2. Clinical Symptoms:

   • Asymptomatic patients: No treatment needed
   • Symptomatic patients: Consider other causes or rare true infection

3. Collection Method:

   • Voided specimens: Higher likelihood of contamination
   • Catheterized specimens: Lower, but still possible contamination

Management Algorithm

For Asymptomatic Patients with Lactobacillus Growth:

• No treatment required
• Document as likely contamination
• Consider improved collection technique for future specimens

For Symptomatic Patients:

1. If urinalysis is normal (no pyuria):

   • Lactobacillus is likely contamination
   • Investigate other causes of symptoms
   • Consider repeat culture with proper collection technique

2. If urinalysis shows pyuria (>250 PMN/mm³):

   • Consider possibility of rare true Lactobacillus UTI 2
   • Consider empiric treatment only if:
     • Symptoms are severe
     • Patient is immunocompromised
     • No other explanation for symptoms exists

3. For immunocompromised patients:

   • Higher vigilance warranted as Lactobacillus can rarely cause true infection in this population 3
   • Consider treatment if symptomatic with pyuria

Antibiotic Selection (If Treatment Deemed Necessary)

If treatment is determined to be necessary (rare cases):

• Erythromycin or clindamycin are typically most effective 4
• Lactobacillus species are generally resistant to:
  • Metronidazole
  • Aminoglycosides
  • Ciprofloxacin
  • Vancomycin (except L. acidophilus) 5

Important Caveats

• Lactobacillus bacteremia is extremely rare but has been associated with 31% mortality at 28 days 3
• Lactobacillus is generally non-pathogenic across all age groups, including immunocompromised individuals 6
• The presence of Lactobacillus in urine may sometimes indicate altered vaginal flora or bacterial vaginosis rather than UTI 1
• In pediatric guidelines, organisms such as Lactobacillus are explicitly noted as "not considered clinically relevant urine isolates for otherwise healthy children" 1

Proper Collection Technique for Future Specimens

To minimize contamination in future specimens:

• Clean-catch midstream collection
• Proper perineal cleansing before collection
• Consider catheterized specimen if contamination is recurrent

Remember that the finding of Lactobacillus in urine culture should prompt consideration of specimen collection quality rather than immediate antibiotic treatment in most cases.