Urine Culture Analysis - Prakash Thapa (38M)

What the Report Shows

1. Citrobacter freundii - with Antimicrobial Susceptibility Test (AST) results shown
2. Acinetobacter calcoaceticus-baumannii complex - AST results cut off (not visible in image)

Citrobacter freundii Sensitivity Pattern

Antibiotic Recommendation

• Colistin is renally excreted and achieves high urinary concentrations, which can overcome intermediate MIC results in the urinary tract
• This is an important consideration - a drug showing "I" (intermediate) in serum may still be effective in urine due to concentration effect

• Colistin (Colistimethate sodium / CMS) IV or oral colistin sulphate, dosed based on renal function
• Typical IV dose: 2.5-5 mg/kg/day of colistin base activity (CBA), divided every 8-12 hours, adjusted for eGFR
• For uncomplicated UTI: oral colistin sulphate (not well absorbed systemically, but active locally in gut/urine) is sometimes used

1. Check the Acinetobacter baumannii AST - the report is cut off. If colistin is sensitive for both organisms, a single agent may suffice. This organism is known to commonly be colistin-susceptible when pan-resistant otherwise.
2. Combination therapy consideration: For XDR organisms, some authorities recommend Colistin + Fosfomycin (if susceptibility tested) or Colistin + Rifampicin for enhanced efficacy, though evidence is mixed for UTI.
3. Fosfomycin - this was NOT tested in the susceptibility panel. Request fosfomycin susceptibility testing, as it retains activity against many MDR gram-negatives and is concentrated in urine. It is an excellent oral option for XDR UTIs.
4. Nitrofurantoin - also not tested; worth requesting for lower UTI if infection is uncomplicated (not effective for upper UTI/urosepsis).

Clinical Priority Points

• This patient has a polymicrobial XDR UTI - a serious situation requiring infectious disease consultation
• Determine if this is lower UTI (cystitis) vs. upper UTI (pyelonephritis/urosepsis) - this changes management significantly
• Colistin is nephrotoxic - monitor renal function closely
• The MIC of ≤1 µg/mL for colistin is at the susceptible/intermediate border per EUCAST; CLSI often interprets MIC ≤2 as susceptible for some organisms
• Request fosfomycin susceptibility urgently - if sensitive, oral fosfomycin 3g single dose (for cystitis) or extended course is a far safer alternative

Revised Assessment: No Antibiotic Treatment Needed

The Key Clinical Point: Asymptomatic Bacteriuria (ASB)

"The presence of asymptomatic bacteriuria often leads to improper antimicrobial treatment in patients with indwelling urinary catheters. Apart from pregnant patients, most others need not undergo urine culture or treatment for asymptomatic bacteriuria."

"Antibiotic treatment of asymptomatic bacteriuria in a patient with a short-term indwelling urinary catheter is not recommended, unless the patient is pregnant or a urologic procedure is immediately pending."

What to Do Instead

When Would Antibiotics Be Justified Here?

• New onset fever (>38°C)
• Rigors / chills
• Altered mental status (with no other cause)
• Flank pain / costovertebral angle tenderness
• Pelvic discomfort
• Acute hematuria
• If a urologic procedure (e.g., cystoscopy, catheter change under infected conditions) is planned imminently

Bottom Line

• Harrison's Principles of Internal Medicine, 22E - Catheter-associated urinary tract infections
• Tintinalli's Emergency Medicine - Complications of Urinary Catheters

Revised Assessment: Active Infection - Treatment IS Required

Why This Is Now a True Infection

1. Psychosis NOS - the patient cannot reliably report subjective symptoms (dysuria, pelvic pain, malaise)
2. Immunosuppression from antipsychotic medications can blunt fever response

Treatment Plan

Step 1 - Immediate (Do Right Now)

• The catheter biofilm harbors XDR organisms protected from antibiotics
• Replacing it removes the primary source
• Do this before or simultaneously with starting antibiotics, not after

Step 2 - Send Additional Susceptibility Tests

Step 3 - Antibiotic Treatment

Regimen:

Critical note on "Intermediate" MIC: The colistin MIC was ≤1 µg/mL. For urinary infections, colistin achieves urine concentrations of 25-200 µg/mL after IV dosing - far exceeding the MIC. What appears "intermediate" systemically is effectively susceptible in the urinary tract. This makes colistin a rational choice specifically for UTI.

If fosfomycin comes back sensitive:

• Fosfomycin IV 8g q8h or oral fosfomycin trometamol 3g every 48-72h (extended course for complicated UTI)
• Fosfomycin + Colistin combination has synergistic data for XDR organisms and reduces colistin nephrotoxicity by allowing lower colistin doses

For the Acinetobacter baumannii complex (AST results were cut off in the report):

• Obtain the full AST for the Acinetobacter - it almost certainly also shows colistin as the only active agent
• If both organisms are colistin-susceptible (intermediate or better), a single agent covers both

Summary of Action Steps

1. Replace the suprapubic catheter now
2. Request fosfomycin and nitrofurantoin susceptibility urgently
3. Start IV Colistin (CMS) - loading dose then maintenance, dose-adjusted for renal function
4. Monitor renal function daily - colistin is nephrotoxic, especially in combination with antipsychotics (some of which are also nephrotoxic)
5. Obtain the full Acinetobacter AST from the lab (it was cut off in the report)
6. Infectious disease consultation - XDR polymicrobial UTI in a psychiatric patient warrants specialist input

Antibiotic to Use

Colistin (Colistimethate Sodium / CMS) IV

Practical Dosing

Why Colistin Works Here Despite "Intermediate" Result

Do Alongside Antibiotics

• Replace the suprapubic catheter (biofilm will sabotage any antibiotic otherwise)
• Request fosfomycin susceptibility - if sensitive, add it to colistin for synergy and to reduce colistin nephrotoxicity
• Monitor creatinine daily - colistin is nephrotoxic
• Get complete Acinetobacter AST (that part of the report was cut off)

Why It Won't Work

What to Do Instead

• Contact pharmacy urgently for Colistimethate Sodium (CMS)
• Consider urgent ID/urology referral while sourcing the drug
• Replace the catheter in the meantime - this alone reduces bacterial load