Treatment of Group B Streptococcus (GBS) Urinary Tract Infection
For urinary tract infections caused by Group B Streptococcus (beta-hemolytic streptococcus group B), treat with ampicillin or penicillin as first-line therapy, with treatment duration of 10 days minimum to ensure complete bacterial eradication. 1, 2, 3
First-Line Antibiotic Selection
Penicillins are the drugs of choice for GBS UTI:
- Ampicillin 500 mg orally four times daily is the preferred agent for genitourinary tract infections 2
- Penicillin V potassium is an alternative oral option, though ampicillin achieves better urinary concentrations 3
- All GBS isolates demonstrate 100% susceptibility to penicillin and ampicillin in vitro 4, 5
- Beta-lactam antibiotics remain the cornerstone of therapy for all invasive beta-hemolytic streptococcal infections 6
Treatment Duration and Monitoring
Minimum 10-day treatment course is mandatory:
- Treatment must continue for at least 10 days to eliminate the organism and prevent sequelae 7, 3
- Obtain follow-up urine cultures 7-14 days after completing therapy to confirm bacterial eradication 2
- In chronic or stubborn infections, treatment for several weeks may be necessary with frequent bacteriologic monitoring 2
Alternative Agents for Penicillin Allergy
If penicillin-allergic, consider these alternatives based on susceptibility:
- Clindamycin 150-300 mg orally every 6 hours for serious infections; must continue for at least 10 days for beta-hemolytic streptococcal infections 7
- Erythromycin or clarithromycin (resistance rates <5% for GBS) 5
- Cephalosporins if no history of severe penicillin allergy 5
Special Considerations for GBS Bacteriuria
GBS bacteriuria requires specific management approach:
- Any quantity of GBS bacteriuria (even asymptomatic) in pregnant women warrants treatment at diagnosis plus intrapartum prophylaxis 1
- In non-pregnant adults, GBS bacteriuria signals need for screening for underlying urinary tract abnormalities (present in 60% of cases) 8
- GBS UTI in non-pregnant adults is associated with chronic renal failure (27% of cases) and community acquisition (65% of cases) 8
- Identify and treat potential reservoirs outside the urinary system (vagina, urethra, gastrointestinal tract) for successful eradication 4
Antibiotics to Avoid
Do not use the following agents for GBS UTI:
- Cotrimoxazole (TMP-SMX): 100% resistance in GBS isolates 5
- Fusidic acid: 100% resistance in GBS isolates 5
- Fosfomycin: Only 69% susceptibility in GBS 5
- Gentamicin and aminoglycosides: GBS demonstrates resistance 8
- Tetracyclines: High resistance rates (74.5% for tetracycline, 72.4% for doxycycline) 5
Clinical Pitfalls
Key considerations to ensure treatment success:
- Do not rely on oral therapy in severely ill patients with nausea, vomiting, or gastrointestinal hypermotility 3
- Ampicillin should be administered at least 30 minutes before or 2 hours after meals for maximal absorption 2
- Poor clinical outcome occurs in 18% of GBS UTI cases despite treatment, emphasizing importance of identifying underlying urinary tract abnormalities 8
- GBS accounts for only 2% of positive urine cultures but represents a significant pathogen requiring thorough evaluation 8