Treatment of Streptococcus agalactiae UTI
For Streptococcus agalactiae (Group B Streptococcus) urinary tract infections, ampicillin or amoxicillin is the drug of choice, with excellent in vitro susceptibility (>95%) and proven clinical efficacy. 1, 2, 3
First-Line Treatment Recommendations
For Adults and Non-Pregnant Women
Ampicillin 500 mg four times daily for 7-14 days is the preferred regimen. 1, 2 The FDA-approved dosing for genitourinary tract infections is 500 mg every 6 hours in equally spaced doses, with severe or chronic infections potentially requiring larger doses 1.
- Amoxicillin 500 mg three times daily is an equally effective alternative, demonstrating 2.5 times greater in vitro activity than ampicillin (MIC 0.03-0.5 mg/L vs 0.1->1 mg/L) 4.
- Treatment duration should be 7-14 days minimum, with therapy continued for at least 48-72 hours after symptom resolution 1.
- Administer ampicillin at least 30 minutes before or 2 hours after meals for maximal absorption 1.
For Men
Ampicillin 500 mg four times daily for 7-14 days, with consideration for 14-day duration when prostatitis cannot be excluded 5, 1.
- Men with S. agalactiae UTI often have underlying chronic diseases or urinary tract abnormalities requiring thorough evaluation 2, 3.
- Prolonged intensive therapy is needed for complications such as prostatitis and epididymitis 1.
Alternative Antibiotic Options
When ampicillin/amoxicillin cannot be used, the following alternatives demonstrate high susceptibility:
- Cephalothin (100% susceptibility) 6
- Nitrofurantoin 100 mg twice daily for 5 days (95.5% susceptibility) 6, 5 - appropriate for uncomplicated lower UTI only
- Norfloxacin (96.9% susceptibility) 6
- Vancomycin (95% susceptibility) 6 - reserved for serious infections
Avoid trimethoprim-sulfamethoxazole despite in vitro synergy with sulphadiazine, as sulphadiazine alone shows complete resistance (MIC >500 mg/L) 4. Clinical resistance to co-trimoxazole reaches 68.9% 6.
Avoid tetracycline due to high resistance rates (81.6%) 6.
Critical Management Considerations
Identify and Treat Reservoirs
Success requires identifying all infection reservoirs beyond the urinary tract 2:
- In women: perform vaginal and rectal cultures to detect colonization 2, 3
- In men: obtain urethral specimens if recurrent infection occurs 3
- Gastrointestinal tract colonization should be considered 2
For women with concurrent vaginal colonization, add topical treatment with 2% chlorhexidine vaginal lavages to systemic antibiotics 3.
Special Populations
Pregnant women with S. agalactiae bacteriuria:
- 53% present with asymptomatic bacteriuria 7
- 35.3% have vaginal/urethral colonization requiring treatment 7
- Ampicillin remains the drug of choice 1, 2
Elderly patients (>60 years):
- Higher prevalence of S. agalactiae UTI, particularly in women over 40 years 7
- 42.2% of non-complicated cystitis cases occur in patients >60 years 7
- Often have underlying chronic diseases requiring longer treatment courses 2, 7
Clinical Pitfalls to Avoid
Do not use single-dose therapy - S. agalactiae requires minimum 7-14 day treatment courses unlike typical E. coli cystitis 1, 2.
Do not assume treatment success without follow-up cultures - obtain cultures 7-14 days after therapy completion from original infection site 1. In women, obtain both endocervical and anal canal cultures 1.
Do not overlook complicated infections - 19.1% of non-pregnant adults with S. agalactiae UTI have complicated infections requiring extended therapy 7.
Stubborn infections may require treatment for several weeks with frequent bacteriologic and clinical appraisal during and after therapy 1, 2.
Treatment Monitoring
- Continue therapy for minimum 48-72 hours after patient becomes asymptomatic 1
- For streptococcal infections, minimum 10 days treatment is recommended to guard against rheumatic fever or glomerulonephritis risk 1
- Frequent bacteriologic assessment is necessary for chronic urinary infections, potentially for several months after treatment 1