[Comparison of GeneXpert® vanA/vanB PCR system and culture methods in the surveillance of vancomycin-resistant enterococci]

Vancomycin-resistant enterococci (VRE) are important agents of hospital infections worldwide. Early recognition of VRE colonization is important in the control of hospital infections. The aim of this study was to compare a real-time PCR (Rt-PCR) system and culture methods in the detection of VRE colonization. A total of 210 perirectal swab samples obtained from the patients (142 were in internal and 68 were in surgical intensive care units) hospitalized at Ankara Training and Research Hospital, Turkey between January-September 2013 were included in the study. The samples were simultaneously evaluated with both Rt-PCR (GeneXpert®vanA/vanB, Cepheid, USA) and the culture methods. The samples were cultivated in enterococcosel agar and incubated at 370C for culture. Culture plates were evaluated for three days on a daily basis. Bacterial identification was done by conventional methods and automated Vitek 2.0 system (BioMérieux, France). Antibiotic susceptibility testing was performed by the E-test. VRE was detected in 76 (36.1%) of the samples by the Rt-PCR method; of them 70 were positive for vanA, two for vanB, and four for vanA + vanB. On the other hand, VRE was detected in 71 (33.8%) of the samples by the culture method. Out of 71 samples, colony growth was observed on the first day in 39 cases, on the second day in 29 cases, and on the third day in three cases. The two strains identified as vancomycin-sensitive enterococci by the Vitek 2 Compact system were determined as vanB positive by PCR. These samples were also confirmed as VRE by E-test. The PCR result of a sample which was found to be invalid, also yielded negative result by culture. Five out of the seven culture-negative samples were positive for vanA, and two for vanB by the GeneXpert® system. In our study, the sensitivity, specificity, positive and negative predictive values of the GeneXpert vanA/vanB PCR system were determined as 97.4%, 98.4%, 97.4%, and 97.4%, respectively. Although the GeneXpert® vanA/vanB RT-PCR method seems to be more attractive regarding the turn around time, it has a higher cost than the culture method. Thus, it was concluded that all laboratories should choose the most appropriate method for screening VRE in the hospital setting according to their own capacities.