Treatment of Polymicrobial UTI with Klebsiella oxytoca, Raoultella ornithinolytica, and Proteus mirabilis
For this polymicrobial urinary tract infection, empiric treatment with a fluoroquinolone (ciprofloxacin 500 mg twice daily or levofloxacin 750 mg once daily) for 7-14 days is the recommended first-line approach, provided local fluoroquinolone resistance is ≤10%. 1, 2, 3
Initial Assessment and Culture-Guided Therapy
Obtain urine culture and susceptibility testing immediately to guide definitive antibiotic selection, as this is critical for polymicrobial infections where resistance patterns may vary between organisms 1, 2
Determine if this represents a complicated UTI by assessing for structural abnormalities, recent instrumentation, indwelling catheters, immunosuppression, or prostatic involvement in males 1, 2
All three organisms (K. oxytoca, R. ornithinolytica, and P. mirabilis) are covered by ciprofloxacin according to FDA labeling 4, making fluoroquinolones an excellent empiric choice for this specific combination
First-Line Empiric Treatment Options
Ciprofloxacin 500 mg orally twice daily for 7-14 days is the preferred regimen when local resistance is ≤10% 1, 2, 4
Levofloxacin 750 mg orally once daily for 5-7 days offers equivalent efficacy with improved adherence due to once-daily dosing 1, 2, 3
If local fluoroquinolone resistance exceeds 10%, administer an initial IV dose of ceftriaxone 1g before starting oral fluoroquinolone therapy 1, 2
Treatment duration should be 7 days for uncomplicated cases, extending to 14 days if prostatic involvement cannot be excluded (particularly relevant in males) 2, 3
Alternative Regimens When Fluoroquinolones Are Contraindicated
Third-generation cephalosporins (ceftriaxone 1-2g IV daily or cefixime orally) combined with an aminoglycoside provide broad coverage against all three organisms 1
Ampicillin 1-2g IV every 6 hours plus gentamicin 5 mg/kg IV once daily is effective against susceptible P. mirabilis and K. oxytoca 1, 5
Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 14 days should only be used if susceptibility is confirmed, and requires an initial IV dose of ceftriaxone 1g if used empirically 1, 2
Special Considerations for Raoultella ornithinolytica
R. ornithinolytica is an emerging pathogen with concerning resistance rates: 4% resistant to ceftriaxone, 6% to quinolones, and 13% to trimethoprim-sulfamethoxazole 6
This organism should never be dismissed as a contaminant, as it causes genuine invasive infections including UTIs, bacteremia, and respiratory infections with a 5% mortality rate 6
Broad-spectrum coverage is essential before susceptibility results are available due to the high antimicrobial resistance rates of R. ornithinolytica 6
Critical Pitfalls to Avoid
Never use ampicillin or amoxicillin monotherapy empirically due to high worldwide resistance rates, particularly in K. oxytoca and R. ornithinolytica 1, 2, 6
Do not use β-lactam monotherapy as it has inferior efficacy compared to fluoroquinolones for UTIs 1, 2
Avoid treating asymptomatic bacteriuria, as this fosters antimicrobial resistance and increases recurrent UTI episodes 1, 7
Do not use fluoroquinolones empirically if the patient has recent fluoroquinolone exposure or if local resistance exceeds 10% without an initial parenteral dose 1, 2
Never assume all three organisms have identical susceptibility patterns—tailor therapy once culture results return 7
Reassessment and Follow-Up
Reassess clinical response at 48-72 hours and adjust antibiotics based on culture and susceptibility results 2, 7
If symptoms persist despite treatment, repeat urine culture to assess for ongoing bacteriuria before prescribing additional antibiotics 1
Consider imaging (ultrasound or CT) if there is concern for obstruction, stones, or anatomic abnormalities, particularly in elderly males or those with recurrent infections 2