Accuracy of the VITEK 2 system to identify coagulase-negative staphylococci

Abstract number: 1733_1218

Sáez A., Ruiz del Castillo B., Agüero J., Martínez-Martínez L.

Objective: We have determined the reliability of the identification of coagulase-negative staphylococci (CoNS) with the VITEK 2 system at species level, considering as a reference the results of molecular identification.

Methods: One hundred and sixty-six clinical isolates of CoNS (Oct. 2003-May 2005) and 7 ATCC type strains were evaluated. Bacteria were identified with the VITEK 2 system using ID GP cards. Absence of coagulase was determined with a latex assay (Pastorex® staph-plus, Bio-Rad). Reference identification was established by 16S rDNA sequence analysis; when identification with VITEK 2 and 16S rDNA disagreed, definitive identification was defined after sequencing of the sodA and tuf genes, as previously described (Drancourt et al. JCM 2000; 38: 3623–30 and Heikens el al. JCM 2005; 43: 2286–90). For species assignation, the sequences of 16S rDNA, sodA and tuf were compared with those in GenBank. Homology values above 97% were considered reliable.

Results: All 7 ATCC strains were correctly identified by 16S rDNA sequencing. Among the 166 clinical isolates, the molecular method identified the following species (number): S. hominis (39), S. haemolyticus (35), S. saprophyticus (30), S. epidermidis (25), S. lugdunensis (12), S. schleiferi (7), S. capitis (7), S. simulans (4), S. pasteuri (2), S. warneri (2), S. intermedius (2) and S. equorum (1). VITEK 2 correctly identified 6 out of the 7 ATCC strains and 151/166 (91%) clinical isolates, including 38/39 S. hominis, 11/12 S. lugdunensis, 5/7 S. capitis, 3/4 S. simulans. Most misidentifications occurred with S. epidermidis (4/25: 3 as S. hominis and 1 as S. intermedius/S. chromogenes), S. saprophyticus (3/30: 1 as S. hominis, 1 as S. warneri and 1 as S. cohnii) and S. haemolyticus (3/32: 1 as S. hominis, 1 as S. warneri and 1 as S. warneri/S. haemolyticus). All isolates of S. schleiferi, S. intermedius, S. pasteuri, S. warneri and S. equorum were correctly identified by the VITEK 2 system.

Conclusions: The VITEK 2 system allows reliable identification of CoNS at species level, but additional improvement would be necessary for identifying S. epidermidis, S. saprophyticus and S. haemolyticus.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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