How do I order a urine culture for Corynebacterium (C.) urealyticum?

How to Order Urine Culture for Corynebacterium urealyticum

When suspecting C. urealyticum infection, you must specifically request the laboratory to use prolonged incubation (48-72 hours) on selective media and alert them to look for this slow-growing organism, as routine urine culture protocols will miss it.

When to Suspect C. urealyticum Infection

You should consider testing for C. urealyticum when patients present with:

• Alkaline urine pH (>7.0) with struvite crystals, leukocytes, and erythrocytes on urinalysis 1
• Chronic or recurrent UTI symptoms despite previous antibiotic treatment 2
• Underlying urinary tract disease (stones, obstruction, anatomic abnormalities) 2
• Recent urological manipulation or prolonged catheterization 2
• Prolonged hospitalization with previous antibiotic exposure 2

Specimen Collection

Collect urine using the most reliable method available:

• For catheterized patients: Aspirate urine from the catheter sampling port after cleaning with 70-90% alcohol 3
• For non-catheterized patients: Obtain a clean-catch midstream specimen 3
• Never collect from drainage bags as bacterial multiplication occurs and leads to misdiagnosis 3

Critical Laboratory Communication

You must communicate directly with the microbiology laboratory and specify:

1. Request prolonged incubation for 48-72 hours (standard 24-hour protocols will miss C. urealyticum) 1
2. Request selective media such as CBU agar, which facilitates detection by reducing competing flora 4
3. Alert them to the clinical suspicion of C. urealyticum, as routine protocols rarely detect this organism 1
4. Note the alkaline urine pH if present, as this is a key clinical clue 1

Specimen Transport and Processing

• Transport specimens promptly to the laboratory and process immediately 3
• If transport delayed >1 hour: Refrigerate the specimen at 5°C 3
• For remote laboratory sites: Use a urine preservative device containing boric acid 3

Interpretation Considerations

C. urealyticum has unique characteristics that affect interpretation:

• The organism is slow-growing and may require 48-72 hours for visible colonies 1, 4
• Low colony counts (<10⁴ CFU/ml) may still be clinically significant when C. urealyticum is isolated, especially with alkaline urine and symptoms 4
• Multidrug resistance is common (97.5% of isolates), particularly to ampicillin (100%), erythromycin (95%), and levofloxacin (95%) 5
• Vancomycin shows universal susceptibility, while linezolid and rifampicin demonstrate good activity 5

Common Pitfalls to Avoid

• Do not rely on routine urine culture protocols without specific laboratory notification, as C. urealyticum will be missed 1
• Do not dismiss alkaline urine as insignificant - this is a critical clue for C. urealyticum infection 1
• Do not assume contamination when Corynebacterium species are isolated from alkaline urine with pyuria 1, 2
• Do not use empiric beta-lactam therapy as all C. urealyticum strains are ampicillin-resistant 5

Clinical Urgency

Early identification is critical because chronic C. urealyticum infection leads to serious complications including alkaline-encrusted cystitis, rapid struvite stone formation, luminal and parenchymal calcification, and progressive renal failure 6. Aggressive management with appropriate antimicrobials and test of cure are essential to prevent these sequelae 6.