Does isolation of Raoultella planticola from a urine culture indicate a urinary tract infection and what is the appropriate treatment?

Raoultella planticola in Urine Culture: Clinical Significance and Management

Isolation of Raoultella planticola from urine most commonly represents colonization or contamination rather than true infection, and treatment should be initiated only when both pyuria (≥10 WBC/HPF or positive leukocyte esterase) and acute urinary symptoms (dysuria, frequency, urgency, fever >38.3°C, or gross hematuria) are present.

Understanding Raoultella planticola as a Uropathogen

R. planticola is a gram-negative, aerobic bacterium of the Enterobacteriaceae family that is predominantly found in soil, water, and aquatic environments, with typical human reservoirs including the gastrointestinal and upper respiratory tracts 1, 2. This organism is an uncommon human pathogen that has been associated with urinary tract infections in fewer than 10 published adult cases and only two pediatric cases prior to 2021 3, 1.

Patient Populations at Risk

The organism appears to preferentially infect specific vulnerable populations:

• Elderly patients constitute the majority of cases, with a mean age of 77 years in the largest published cohort 1
• Immunocompromised individuals, including those with HIV infection, multiple myeloma, or on chemotherapy, show increased susceptibility 4, 5
• Patients with diabetes mellitus represent the most common comorbidity, present in 43% of cases in one series 1
• Children with congenital anomalies of kidney and urinary tract (CAKUT) may be at particular risk, as the association has been documented 3
• Patients with renal failure demonstrate higher proportions of infection compared to the general population 1

Diagnostic Criteria for True Infection vs. Colonization

Before initiating antimicrobial therapy, you must document BOTH of the following:

1. Pyuria: ≥10 WBC/HPF on microscopy OR positive leukocyte esterase 6, 7
2. Acute urinary symptoms: dysuria, frequency, urgency, suprapubic pain, fever >38.3°C, or gross hematuria 6, 7

If either criterion is absent, the finding represents asymptomatic bacteriuria and should NOT be treated 6, 7. This principle applies equally to R. planticola as to more common uropathogens—the organism's rarity does not justify deviation from standard diagnostic criteria.

Common Pitfall: Treating Based on Culture Alone

The presence of R. planticola in urine without symptoms does not warrant treatment, even in immunocompromised patients 6, 7. Treating asymptomatic bacteriuria provides no clinical benefit, promotes antimicrobial resistance, and increases the risk of Clostridioides difficile infection and reinfection with more resistant organisms 6, 7.

Clinical Spectrum of R. planticola UTI

When true infection occurs, the severity ranges widely:

• Simple cystitis was documented in 15 of 37 patients (41%) in the largest series 1
• Altered mental status was the most common presenting complaint, followed by fever 1
• Urosepsis occurred in 2 patients (5%) 1
• Septic shock developed in 2 patients (5%), though no mortalities were reported in this cohort 1

The average length of stay was 3 days, with an average antibiotic duration of 8 days 1.

Antimicrobial Susceptibility and Treatment Selection

Intrinsic Resistance Pattern

Ampicillin resistance is an intrinsic characteristic of Raoultella species, documented in 35 of 37 isolates (95%) in the largest published series 1. This resistance pattern mirrors that of Klebsiella species and should be anticipated when selecting empiric therapy.

First-Line Treatment Options

For uncomplicated cystitis caused by susceptible R. planticola:

• Ciprofloxacin 500 mg orally twice daily for 3 days was the most frequently prescribed antibiotic in published cases 1
• First-generation cephalosporins (e.g., cephalexin) have been successfully used, particularly in pediatric cases with CAKUT requiring long-term suppression 3
• Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days may be used if the organism is susceptible and local resistance is <20% 8

For complicated UTI or pyelonephritis:

• Ciprofloxacin 500-750 mg twice daily for 7-10 days or levofloxacin 750 mg daily for 5-7 days 8
• Third-generation cephalosporins (ceftriaxone 1-2 g IV daily) for 7-14 days in severe cases 8
• Duration should be 7-14 days for complicated infections 9, 8

Emerging Resistance Concerns

While most isolates remain susceptible to fluoroquinolones and cephalosporins, carbapenemase production has been documented in R. planticola, including KPC-producing strains 2. In one published case, successful treatment required ceftazidime/avibactam plus polymyxin 2. Additionally, 2 of 37 isolates in one series were multidrug-resistant, though still susceptible to ciprofloxacin 1.

Always obtain urine culture with susceptibility testing before finalizing therapy to detect resistance patterns 8.

Special Clinical Scenarios

Pediatric Patients with CAKUT

Children with UTI caused by R. planticola may have underlying congenital anomalies of kidney and urinary tract 3. Actively screen for CAKUT with renal ultrasound and consider voiding cystourethrogram or magnetic resonance urography if hydronephrosis or obstruction is suspected 3.

For children with confirmed CAKUT and recurrent UTI risk:

• Long-term prophylaxis with first-generation cephalosporins (cephalexin 10 mg/kg daily) can prevent recurrence 3
• Avoid unnecessary broad-spectrum antibiotics to prevent antimicrobial resistance 3
• Use sufficiently strong antibiotics for appropriate duration during acute infection, as R. planticola can be life-threatening 3

Immunocompromised Patients

In patients with HIV, multiple myeloma, or other immunosuppressive conditions, R. planticola represents a potential emerging pathogen 4, 5. However, the same diagnostic criteria apply—do not treat asymptomatic bacteriuria even in immunocompromised hosts 6, 7.

For confirmed infection in immunocompromised patients:

• Obtain blood cultures if fever, rigors, or hemodynamic instability is present 7
• Consider longer treatment duration (10-14 days) given the potential for more severe disease 9, 8
• Reassess at 48-72 hours; if fever persists or clinical deterioration occurs, obtain imaging to exclude complications 9

Catheterized Patients

Do not screen for or treat asymptomatic bacteriuria in catheterized patients, as bacteriuria and pyuria are nearly universal in this population 6, 7. Reserve testing for patients with fever, hypotension, rigors, or suspected urosepsis 7.

Practical Management Algorithm

Step 1: Assess for acute urinary symptoms

• Dysuria, frequency, urgency, suprapubic pain, fever >38.3°C, or gross hematuria present? 6, 7
  • NO → Do not treat; this is asymptomatic bacteriuria 6, 7
  • YES → Proceed to Step 2

Step 2: Confirm pyuria

• ≥10 WBC/HPF on microscopy OR positive leukocyte esterase? 6, 7
  • NO → UTI unlikely; consider alternative diagnoses 7
  • YES → Proceed to Step 3

Step 3: Classify infection severity

• Systemic signs (fever >38.3°C, rigors, hypotension, altered mental status)? 7, 1
  • NO → Treat as uncomplicated cystitis (3-7 days) 8
  • YES → Treat as complicated UTI/pyelonephritis (7-14 days) 9, 8

Step 4: Select empiric therapy

• Uncomplicated: Ciprofloxacin 500 mg PO BID × 3 days OR first-generation cephalosporin 3, 1
• Complicated: Ciprofloxacin 500-750 mg PO BID × 7-10 days OR ceftriaxone 1-2 g IV daily × 7-14 days 8
• Avoid ampicillin due to intrinsic resistance 1

Step 5: Adjust based on susceptibilities

• Narrow or broaden therapy according to culture results 8
• If carbapenemase-producing, consult infectious disease for ceftazidime/avibactam or alternative 2

Key Takeaways

• R. planticola in urine is most often colonization; treat only when both pyuria and acute urinary symptoms are present 6, 7, 1
• Ampicillin resistance is intrinsic; avoid β-lactam monotherapy without susceptibility data 1
• Ciprofloxacin remains the most commonly used and effective agent for susceptible isolates 1
• Screen for CAKUT in pediatric cases and consider long-term prophylaxis if structural abnormalities are found 3
• Carbapenemase production is emerging; always obtain susceptibility testing 2
• Do not treat asymptomatic bacteriuria, even in immunocompromised or elderly patients 6, 7