Treatment of Urinary Tract Infection Caused by Streptococcus agalactiae
For patients with symptomatic UTI caused by Streptococcus agalactiae (Group B streptococcus), ampicillin 500 mg four times daily for 7 days is the recommended first-line treatment based on high susceptibility patterns.
Antibiotic Selection for S. agalactiae UTI
First-line options:
- Ampicillin: 500 mg orally four times daily for 7 days 1
- Studies show >95% sensitivity of S. agalactiae to ampicillin
- Dosing should be spaced equally throughout the day
- Should be taken at least 30 minutes before or 2 hours after meals for optimal absorption 2
Alternative options (if penicillin allergy or resistance):
- Cephalexin: 500 mg orally four times daily for 7 days 3
- Amoxicillin with clavulanate: 500/125 mg orally three times daily for 7 days 3
- Nitrofurantoin: 100 mg orally twice daily for 5-7 days (only for uncomplicated lower UTI) 4
Treatment Duration
- 7 days is the recommended duration for patients with prompt symptom resolution 3
- 10-14 days is recommended for patients with delayed response or complicated infection 3
Special Considerations
Diagnostic Approach
- Obtain urine culture prior to initiating antibiotics to confirm the causative organism and susceptibility 3
- Do not rely solely on dipstick testing as it has limited predictive value 3
- Ensure proper collection technique to minimize contamination
Treatment Modifications
- For complicated UTI or pyelonephritis: Consider broader coverage initially while awaiting culture results, then narrow therapy based on susceptibility
- For patients with indwelling catheters: Replace catheter before collecting urine culture and starting antibiotics if the catheter has been in place for >2 weeks 3
- For elderly patients: Monitor for adverse effects and drug interactions more closely
Monitoring and Follow-up
- Clinical improvement should be expected within 48-72 hours of starting appropriate therapy 4
- Follow-up cultures are generally not necessary for uncomplicated infections with complete symptom resolution
- For complicated or recurrent infections, consider investigating potential reservoirs (vaginal, urethral, gastrointestinal) 1
Important Caveats
- S. agalactiae UTIs are increasingly recognized in non-pregnant adults, particularly in women over 40 years of age 5
- High resistance to tetracycline (81.6%) and co-trimoxazole (68.9%) has been reported, making these poor empiric choices 6
- S. agalactiae can cause invasive infections including meningitis and endocarditis, especially in patients with diabetes or other comorbidities 7
- For pregnant women with S. agalactiae in urine, different management protocols apply (not covered in this response)
Remember that S. agalactiae UTIs may require thorough examination to identify all potential infection foci, including those outside the urinary system, to prevent recurrence 1.