Evaluation of a Rapid Enrichment-PCR Method for the Detection of vanA Vancomycin-resistant Enterococci in Fecal Specimens

Kim, Sollip; Sung, Heungsup; Jeon, Hong Sun; Park, Suk Ja; Park, Sang Hyuk; Kim, Mi Na

Abstract

BACKGROUND: Rapid and accurate surveillance is crucial in controlling vancomycin-resistant enterococci (VRE). Culture-based surveillance takes more than 4 days and direct polymerase chain reaction (PCR) is rapid but compromised by a low sensitivity. In this study, we evaluated the performance of an enrichment-PCR method for vanA VRE surveillance.
METHODS
In July 2006, 100 fecal specimens were inoculated to Enterococcosel agar (EA) and Enterococcosel broth (EB) containing 6 microgram/mL vancomycin. After 1 or 2 day-incubation bacterial pellets were obtained from 1 mL of blackened EB and VanA PCR were performed with DNA extract of the pellets (EB+PCR). Blackened EB were also subcultured on EA (EB+EA). Black colonies on EA were submitted to identification and antimicrobial susceptibility test and, if necessary, they were confirmed with vanA PCR. The electronic medical records were reviewed for previous history of colonization or infection of VRE.
RESULTS
A total of 59 specimens were positive for VRE by at least one method. VanA VRE was detected from 43, 54, and 53 specimens by EA, EB+ PCR, and EB+EA, respectively; 54 EB+PCR positive specimens comprised 43 EA-positive, 7 EA-negative/ EA+EB-positive and 4 EB+PCR-only-positive, and 11 EA-negative/EB+PCR-positive specimens were from the previous VRE-colonizers. The five EB+PCR-negative specimens were EB+EA-positive, suggesting false negativity, probably due to PCR inhibitors. The average turn-around time for EA was 88+/-35 h, whereas 98% of EB+PCR positive results were obtained at day 1.
CONCLUSION
Enrichment in EB followed by PCR (EB+ PCR) appears to be a rapid and sensitive method for the detection of vanA VRE in stool specimens. Internal control would be required to detect false negative results.