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

Abstract

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.Catalase-negative, gram-positive cocci are a heterogeneous group of 17 genera that include streptococci, enterococci, and nonstreptococcal, nonenterococcal species (9, 10). Over 70 streptococcal and enterococcal species have been implicated in human disease (10,27). Of these, only a few are known to cause important infections (e.g., Streptococcus pneumoniae, Streptococcus pyogenes, Streptococcus agalactiae, Enterococcus faecalis, Enterococcus faecium, and viridans group streptococci).A number of manual, semiautomated, and automated systems are reported to produce acceptable identification (ID) results for S. pneumoniae, beta-hemolytic streptococci, and enterococcal species (26,27). These systems, however, were shown not to be sufficiently accurate in identifying streptococci of the viridans group (13, 20), organisms of complex taxonomy (2, 10, 26). The performance of some automated systems has been evaluated with regard to catalase-negative, gram-positive cocci (7,13,14,17,24). Reproducibility and accuracy of results, turnaround time, availability of data for epidemiological monitoring, and cost-effectiveness constitute the main reasons supporting the choice of automated systems.Becton Dickinson (BD Diagnostic Systems, Sparks, MD) has introduced the Phoenix automated microbiology system for ID and antimicrobial susceptibility testing (AST) of human pathogen...

It's Not Easy Being Green: the Viridans Group Streptococci, with a Focus on Pediatric Clinical Manifestations

“…Of 22 S. anginosus group isolates, 18 were correctly identified and 4 were discordant. A second study evaluated the Phoenix SMIC/ID-2 panel using the API 20 Strep system as a comparator method (resolving discrepant results via 16S rRNA gene sequencing and amplification and sequencing of housekeeping genes) (5). For the VGS, 31 isolates were assayed, with only 53% concordance between the Phoenix and reference methods for S. mitis group organisms, 100% concordance for the S. anginosus group, and 75% concordance for S. sanguinis group organisms (5).…”

Identification of Clinical Isolates of α-Hemolytic Streptococci by 16S rRNA Gene Sequencing, Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry Using MALDI Biotyper, and Conventional Phenotypic Methods: a Comparison

“…Taxonomy and nomenclature followed that outlined by Facklam at the CDC's Streptococcal Laboratory, Atlanta, GA (15), and subsequently cited and expanded upon by others (11, 24). Unlike previous studies of phenotypic methods (5,6,12,16,19,20), this was a direct comparison of phenotypic methods versus the gold standard.Bacterial isolates. Forty-nine clinically relevant isolates (40 blood culture, 2 cerebrospinal fluid (CSF), 3 urine, 1 each from ascitic fluid, joint fluid, and an infected wound, and 1 from an unspecified site but referred as clinically significant) of ␣-hemolytic streptococci (except Streptococcus pneumoniae) were collected prospectively from sterile sites cultured in three clinical laboratories.…”

“…Taxonomy and nomenclature followed that outlined by Facklam at the CDC's Streptococcal Laboratory, Atlanta, GA (15), and subsequently cited and expanded upon by others (11,24). Unlike previous studies of phenotypic methods (5,6,12,16,19,20), this was a direct comparison of phenotypic methods versus the gold standard.…”

Rapid Identification of Viridans Streptococci by Mass Spectrometric Discrimination

“…Phenotypic test systems do not always allow the accurate identification of some species in this heterogeneous group of bacteria (3,10). Several molecular methods for the identification of VS to the species level have been developed.…”