Vancomycin-Resistant Enterococcus (VRE)

Enterococci commonly live in the gastrointestinal tract without causing illness. VRE are Enterococcus species that have acquired vanA or vanB resistance genes. These genes alter the bacterial cell-wall target so vancomycin can no longer bind effectively; the result is high-level resistance, with a vancomycin minimum inhibitory concentration (MIC) of at least 32.0 mg/L. Vancomycin is therefore ineffective against a confirmed VRE infection. The organism may remain in the bowel or appear in a specimen without invading tissue. That state is colonization. Antibiotic exposure, especially prolonged broad-spectrum therapy or vancomycin use, can suppress competing bacteria and allow VRE to persist. Hospitalization, invasive devices, wounds, urinary catheters, and reduced host defenses increase the chance that carriage will progress to infection. The first clinical question is not simply, “Is VRE present?” It is, “Is this patient ill from VRE?” The answer depends on the specimen, the patient’s symptoms, objective findings, and the presence of another explanation for the result. A resistant culture can be clinically significant, but it can also represent harmless carriage.