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Journal of Clinical Microbiology, September 2006, p. 3263-3267, Vol. 44, No. 9
0095-1137/06/$08.00+0     doi:10.1128/JCM.00299-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Use of the Phoenix Automated System for Identification of Streptococcus and Enterococcus spp.

Laboratory of Medical Microbiology, Ospedale di Circolo and University of Insubria, Varese,¹ Department of Molecular Biology, University of Siena, Siena,² Department of Microbiological Sciences, University of Catania, Catania, Italy³

Received 10 February 2006/ Returned for modification 3 April 2006/ Accepted 10 July 2006

The Phoenix system (Becton Dickinson Diagnostic Systems, Sparks, MD) was evaluated for identification (ID) to the species level of streptococci and enterococci. Two hundred clinical isolates were investigated: beta-hemolytic streptococci (n = 50), Streptococcus pneumoniae organisms (n = 46), viridans group streptococci (n = 31), Enterococcus faecium (n = 36), Enterococcus faecalis (n = 25), and other catalase-negative cocci (n = 12). The API system (bioMérieux, Marcy l'Étoile, France) was used as a comparator. Molecular methods (sequencing of 16S rRNA and zwf and gki genes and ddl gene amplification) were used to investigate discordant results. Upon resolution of discrepancies, correct species ID was achieved by the Phoenix system for 121/129 (93.8%) streptococci and 63/70 (90.0%) enterococci. Excellent results were obtained for S. pneumoniae (45/45) and beta-hemolytic streptococci (49/50). With regard to viridans streptococci, the accuracy of the Phoenix system was 83.9%. Among the latter organisms, the best performance was obtained with isolates of the Streptococcus sanguinis group and Streptococcus anginosus group; problems were instead encountered with the Streptococcus mitis group. Four E. faecium and three E. faecalis isolates were misidentified as Enterococcus casseliflavus/Enterococcus gallinarum or Enterococcus durans. Thus, these isolates were identified only at the genus level. Compared with commercially available systems, the Phoenix system appears a reliable diagnostic tool for identifying clinically relevant streptococci and enterococci. The SMIC/ID-2 panel proved particularly effective for beta-hemolytic streptococci and pneumococci.

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