How is Enterococcus faecalis detected in urine?

Detection of Enterococcus faecalis in Urine

Enterococcus faecalis in urine is detected through standard urine culture on primary isolation plates, with presumptive identification based on colonial morphology, Gram stain showing gram-positive cocci, and a positive pyrrolidonyl arylamidase (PYR) test. 1

Laboratory Identification Methods

Initial Detection and Presumptive Identification

• Urine culture is performed on standard media, with colonies appearing on primary isolation plates 1
• Colonial morphology provides initial clues to enterococcal presence 1
• Gram stain reveals gram-positive cocci in chains or pairs 2
• PYR test (pyrrolidonyl arylamidase) is the key rapid presumptive test that differentiates enterococci from other gram-positive cocci 1

Species-Level Identification

While presumptive identification is often sufficient for clinical management, species-level identification can be performed when needed:

• Most commercially available identification systems adequately differentiate E. faecalis from other enterococcal species 1
• Biochemical tests can distinguish E. faecalis from E. faecium (E. faecalis is generally more susceptible to penicillin) 1
• Additional testing for motility and pigment production helps differentiate other species like E. gallinarum (motile, nonpigmented) and E. casseliflavus (motile, pigmented) from E. faecium (nonmotile, nonpigmented) 1

Antimicrobial Susceptibility Testing

When to Perform Testing

• Routine susceptibility testing of urine isolates may not be performed in all laboratories, but should be considered when resources permit 1
• Testing is particularly important for determining vancomycin resistance and resistance to penicillin/ampicillin 1
• High-risk patients (ICU, oncology, transplant) should have their enterococcal isolates tested routinely 1

Testing Methods

• Disk diffusion method: Incubate plates for 24 hours and read zones of inhibition using transmitted light 1
• Minimum inhibitory concentration (MIC) can be determined by agar dilution, agar gradient dilution, broth macrodilution, or manual broth microdilution, all incubated for 24 hours 1
• Confirmatory testing for vancomycin resistance: Streak 1 µL of standard inoculum (0.5 McFarland) onto brain heart infusion agar containing 6 µg/mL vancomycin, incubate for 24 hours at 35°C, with any growth indicating resistance 1, 2

Important Clinical Caveats

Automated Testing Limitations

• Fully automated methods for testing enterococcal vancomycin resistance are unreliable and should be avoided 1, 2
• Manual methods are preferred for accurate susceptibility determination 2

Clinical Significance in Urine

• E. faecalis is the most common enterococcal species causing urinary tract infections, accounting for approximately 5% of community-acquired UTIs in children 3
• All E. faecalis strains in research studies have shown consistent susceptibility to vancomycin, nitrofurantoin, and ampicillin in community settings 4, 3
• E. faecalis shows tropism for the kidneys rather than the bladder, making pyelonephritis more common than cystitis 5
• Presence of E. faecalis in urine is highly indicative of underlying urinary tract abnormalities and warrants imaging studies 3

Infection Control Implications

• When vancomycin-resistant enterococci (VRE) are detected in urine, immediately notify infection control personnel and implement isolation precautions 1, 2
• Periodic surveillance of enterococcal isolates from urine should be performed in hospitals, especially in high-risk units 1
• After VRE colonization is detected, all enterococcal isolates including those from urine should be screened routinely for vancomycin resistance 1