What is the treatment for a urine culture positive for Streptococcus mitis/oralis?

Treatment of Streptococcus mitis/oralis in Urine Culture

In most cases, Streptococcus mitis/oralis isolated from urine should NOT be treated, as it is typically a contaminant from normal skin and oral flora rather than a true urinary pathogen.

Initial Assessment: Contamination vs. True Infection

The critical first step is determining whether this represents true infection or contamination:

• S. mitis/oralis is normal oral and skin flora and its presence in urine is generally considered contamination rather than true infection 1
• Contamination rates are notably high for this organism in urine cultures, with studies showing contamination in 43.5% of positive cultures 2
• Do NOT treat asymptomatic bacteriuria with organisms like S. mitis/oralis, as treatment promotes antimicrobial resistance without clinical benefit 3

Evidence Supporting True UTI (When Treatment IS Indicated)

Treat only when ALL of the following are present:

• Clear urinary symptoms including dysuria, urgency, frequency, or suprapubic pain 3, 1
• Polymorphonuclear leukocyte phagocytosis observed on microscopy (strong indicator of true infection rather than contamination) 1
• Repeat positive culture with the same organism, ideally from a properly collected clean-catch or catheterized specimen 3
• Absence of other more likely uropathogens (E. coli, Klebsiella, etc.) that would suggest mixed contamination 3

Antibiotic Selection for Confirmed Infection

When true S. mitis/oralis UTI is confirmed, antibiotic selection is complicated by high rates of multidrug resistance:

First-Line Treatment Options

• Vancomycin is the most reliable choice, with 100% susceptibility in recent studies and proven clinical efficacy in documented S. mitis/oralis UTI 1, 2
• Linezolid also shows 100% susceptibility and can be used as an alternative to vancomycin 2

Important Resistance Patterns to Avoid

• Penicillin shows only 23% susceptibility and should be avoided as empiric therapy 2
• Erythromycin has only 27% susceptibility and is not recommended 2
• Multidrug resistance occurs in 21.6% of isolates, most commonly to β-lactams, erythromycin, and clindamycin 2
• Ceftriaxone susceptibility is only 74.3%, making it unreliable as monotherapy 2

Alternative Options Based on Susceptibility Testing

• Levofloxacin (86.5% susceptibility) can be considered if susceptibility is confirmed 2
• Chloramphenicol (89.2% susceptibility) is an option but rarely used due to toxicity concerns 2
• Clindamycin (67.6% susceptibility) may be considered with documented susceptibility 2

Treatment Duration

• 7-14 days for complicated UTI with systemic symptoms 4
• 7 days for uncomplicated UTI if truly confirmed 4
• 14 days in males where prostatitis cannot be excluded 4

Special Considerations and Pitfalls

High-Risk Populations Requiring Lower Threshold for Treatment

• Patients undergoing endoscopic urologic procedures with anticipated mucosal trauma should receive treatment even if asymptomatic 3
• Pregnant women with asymptomatic bacteriuria require treatment regardless of organism 3
• Patients with indwelling urinary devices may require device removal in addition to antibiotics, as S. mitis/oralis can form biofilms 3

Common Clinical Pitfalls

• Do NOT use vancomycin for routine prophylaxis or for treating presumed infections when cultures are negative 3
• Proper specimen collection is essential to minimize contamination; midstream clean-catch or catheterized specimens are preferred 3
• Pyuria alone does NOT indicate need for treatment in asymptomatic patients, as it increases odds of inappropriate treatment (OR 2.83) 5
• Female sex and gram-negative organisms are associated with overtreatment of asymptomatic bacteriuria, but these factors should not influence treatment decisions for S. mitis/oralis 5

When to Reassess

• If symptoms persist after 48-72 hours of appropriate therapy, repeat urine culture to assess for ongoing bacteriuria or consider alternative diagnoses 4
• Monitor for emergence of resistance, particularly daptomycin resistance if that agent is used for systemic infection, as S. mitis/oralis can rapidly develop high-level resistance 6