Evaluation of VITEK 2 for identification of enterococci and detection of vancomycin resistance

Abstract number: P823

Adler H., Oezcan S., Sax S., Frei R.

Objective: To evaluate the VITEK 2 (bioMerieux, Marcy l'Etoile, France) for the identification of Enterococcus faecalis, E. faecium, E. gallinarum and E. casseliflavus and for the detection of vancomycin resistance.

Methods: We examined a total of 83 enterococcal isolates. Isolates comprised 26 E. faecium and 24 E. faecalis, 26 of them with acquired vancomycin resistance (VanA, VanB). Additionally, 33 isolates with natural vancomycin resistance (22 E. gallinarum, 11 E. casseliflavus) were tested. Isolates were identifided with the VITEK 2 colorimetric GP card. For susceptibility testing the antimicrobial susceptibility testing card P 534 was used. MICs were interpreted using the breakpoints recommended by the CLSI. Identification and vancomycin resistance were molecularly confirmed with the GenoType Enterococcus test (Hain Lifescience, Nehren, Germany) as gold standard.

Results: All isolates of E. faecalis and E. faecium were correctly identified as were 20 of 22 isolates of E. gallinarum and 7 of 11 isolates of E. casseliflavus. In 6 isolates Vitek 2 could not differentiate between E. gallinarum and E. casseliflavus. Vitek 2 results of susceptibility testing are presented in table 1. Vancomycin resistance was detected in all isolates carrying a vanA or vanB gene, thus the test was 100% sensitive for acquired vancomycin resistance. Teicoplanin resistance was missed in one isolate of vanA, consequently the isolate resembled a VanB phenotype. Sensitivity for natural vancomycin resistance (VanC) was 91%. Of the isolates with vanC, 48% had a MIC of geqslant R: gt-or-equal, slanted32 mg/l (resistant), thus resembling a VanB phenotype.

Conclusions: VITEK 2 is an excellent tool for the identification of E. faecalis and E. faecium (100% correct identifications). The system was less able to differentiate between E. gallinarum and E. casseliflavus (82% correct identification, 18% low discrimination). However, since both species have natural resistance to vancomycin, the clinical significance of separating them is minimal. VITEK 2 is a useful means for the detection of vancomycin resistance in enterococci. However, both identification and susceptibility testing should be performed in order not to miss natural vancomycin resistance and to discriminate between natural and acquired vancomycin resistance.

Table 1.

Organism (no.)Susceptibilities as determined by Vitek 2
vanA VRE (12)02101011
vanB VRE (13)01121300
vanA+vanB VRE (1)001100
vanC1 VRE (22)0715000
vanC2 VRE (11)371000
VSE (24)24002400
S sensitive, I intermediate, R resistant.
VRE vancomycin resistant Enterocccus, VSE vancomycin susceptible Enterococcus.

Session Details

Date: 16/05/2009
Time: 00:00-00:00
Session name: 19th European Congress of Clinical Microbiology and Infectious Diseases
Location: Helsinki, Finland, 16 - 19 May 2009
Presentation type:
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