Treatment of Polymicrobial UTI with Aerococcus sanguinicola and Proteus mirabilis with Hematuria
This polymicrobial UTI should be treated as a complicated UTI with empirical intravenous combination therapy using amoxicillin plus an aminoglycoside or a second-generation cephalosporin plus an aminoglycoside for 7-14 days, then tailored based on culture susceptibilities. 1
Classification and Clinical Significance
This infection qualifies as a complicated UTI due to the presence of hematuria, which is a documented risk factor requiring more aggressive management 1. The presence of Proteus mirabilis, a urea-splitting organism, further complicates treatment as it increases stone formation risk and is associated with complicated UTIs 1.
Empirical Antibiotic Selection
Initial Intravenous Therapy
For complicated UTIs with systemic symptoms, strong recommendations support combination therapy 1:
- Amoxicillin plus an aminoglycoside (gentamicin 5 mg/kg daily or amikacin 15 mg/kg daily) 1
- Alternative: Second-generation cephalosporin plus an aminoglycoside 1
- Alternative: Intravenous third-generation cephalosporin (ceftriaxone 1-2g daily or cefotaxime 2g three times daily) 1
Organism-Specific Considerations
Aerococcus sanguinicola demonstrates:
- 100% susceptibility to benzylpenicillin, ampicillin, meropenem, vancomycin, and rifampicin 2, 3
- Intrinsic resistance to nitroxoline (MIC 64-128 mg/L) 2
- Occasional resistance to ciprofloxacin (10.9% of Aerococcus species) 2
Proteus mirabilis commonly shows:
- High resistance to trimethoprim-sulfamethoxazole (80.6%) 4
- Significant resistance to amoxicillin-clavulanate (57.3%) and third-generation cephalosporins (55.3%) 4
- ESBL production in 37.9% of isolates, particularly in complicated cases 4
- Proteus species are common in complicated UTIs alongside Enterococcus and Klebsiella 1
Treatment Duration and Monitoring
Treatment duration should be 7-14 days depending on clinical response 1:
- 7 days minimum if patient becomes hemodynamically stable and afebrile for 48 hours 1
- 14 days recommended if prostatitis cannot be excluded in males or if response is slower 1
Transition to Oral Therapy
Once culture results return and the patient is clinically stable (afebrile >48 hours), tailor therapy to susceptibility results 1:
- If susceptible to ampicillin: Continue oral ampicillin or amoxicillin
- If fluoroquinolone-susceptible and local resistance <10%: Ciprofloxacin 500-750mg twice daily 1
- Avoid ciprofloxacin empirically given 10.9% Aerococcus resistance and only use if susceptibilities confirm sensitivity 1, 2
Critical Pitfalls to Avoid
Do not use fluoroquinolones empirically in complicated UTIs from urology departments or if the patient used fluoroquinolones in the last 6 months due to resistance concerns 1.
Do not use trimethoprim-sulfamethoxazole empirically given the 80.6% resistance rate in Proteus mirabilis 4.
Do not use nitroxoline for this infection as Aerococcus sanguinicola demonstrates intrinsic resistance 2.
Ensure urine culture and susceptibility testing is performed before initiating therapy, as this is mandatory for complicated UTIs 1.
Investigation for Underlying Abnormalities
The presence of gross hematuria with infection warrants imaging evaluation to exclude structural abnormalities, stones (particularly with Proteus), or other complicating factors 1. Proteus mirabilis produces urease leading to struvite stone formation, which can perpetuate infection 1.