Vancomycin-Resistant Enterococcus, Molecular Detection, PCR
Identifying carriers of vancomycin-resistant enterococci
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Vancomycin-resistant enterococci (VRE) are major nosocomial pathogens. Patients who are particularly vulnerable to fatal disease from VRE include those with hematologic malignancies and liver transplants. Nosocomial spread of VRE occurs as the result of fecal carriage. Risks for both colonization and infection include prolonged hospitalization, intensive care unit stay, transplantation, hematologic malignancies, and prolonged exposure to antibiotics.
The Centers for Disease Control and Prevention provides recommendations to prevent the spread of VRE in institutional settings. These recommendations include isolation of patients experiencing active VRE infection, screening of patients by perianal swab or fecal testing to identify carriers of VRE, and subsequent isolation or cohorting of VRE carriers. Identification and isolation of VRE carriers has been shown to be cost-effective.
In Enterococcus faecalis or E faecium, vancomycin resistance is usually associated with the presence of the vanA or vanB genes. The presence of these genes is detected by a molecular method in this assay.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Positive test results indicate the presence of either the vanA or vanB gene, which confers vancomycin resistance in Enterococcus faecalis and Enterococcus faecium (and occasionally other organisms). Patients with a positive test result should be placed in isolation or cohorted with other vancomycin-resistant enterococci (VRE) carriers according to the institution's infection control practices.
A negative result indicates the absence of detectable vanA or vanB DNA in the specimen but does not rule-out carrier status as false-negative results may occur due to inhibition of PCR, sequence variability underlying primers or probes, or the presence of VRE in quantities less than the limit of detection of the assay. In the rare event that PCR testing appears to be negative but there is evidence of PCR inhibition, the result will read "PCR inhibition present," in such a case, a new specimen should be submitted for repeat testing.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
A positive result does not imply the presence of vancomycin-resistant enterococci (VRE) disease; the presence of vanA or vanB genes correlates with colonization by VRE. Colonization with VRE is not associated with any signs or symptoms.
vanA or vanB genes may occasionally be found in organisms other than enterococci.
Perianal swabs (894) were evaluated for the presence of vanA or vanB DNA by the vancomycin-resistant enterococci (VRE) PCR assay and compared to culture using selective and differential media. Compared to culture the VRE PCR assay was 98% sensitive and 98% specific. The VRE PCR assay detected 35 more positive specimens than the culture method. No cross-reactivity was seen when tested on a panel of pathogenic and normal flora bacteria of the gastrointestinal tract. Enterococcus species containing the vanC gene were not detected with the VRE PCR assay.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Sloan LM, Uhl JR, Vetter EA, et al: Comparison of the Roche LightCycler vanA/vanB detection assay and culture for detection of vancomycin-resistant enterococci from perianal swabs. J Clin Microbiol 2004;42:2636-2643
2. Mayo Medical Laboratories Communique: Vancomycin-resistant enterococci: Colonization, infection, detection, and treatment. Vol 32, No. 11, November 2007
3. Zirakzadeh A, Patel R: Epidemiology and mechanisms of glycopeptide resistance in enterococci. Curr Opin Infect Dis 2005;18:507-512
4. Zirakzadeh A, Patel R: Vancomycin-resistant enterococci colonization, infection detection and treatment. Mayo Clinic Proc 2006;81:529-536
5. Patel R: Enterococcal-type glycopeptide resistance genes in non-enterococcal organisms. FEMS Microbiol Lett 2000 Apr 1;185(1):1-7