The performance of the BD Phoenix Automated Microbiology System (BD Diagnostic Systems) was compared to those of the Vitek 2 (bioMérieux), the MicroScan MICroSTREP plus (Siemens), and Etest (bioMérieux) for antibiotic susceptibility tests (AST) of 311 clinical isolates of Streptococcus pneumoniae. The overall essential agreement (EA) between each test system and the reference microdilution broth reference method for S. pneumoniae AST results was >95%. For Phoenix, the EAs of individual antimicrobial agents ranged from 90.4% (clindamycin) to 100% (vancomycin and gatifloxacin Streptococcus pneumoniae is the leading cause of communityacquired pneumonia in adults and serious respiratory infections in children in the United States. Globally, septicemia is a major cause of infant mortality in developing nations. Penicillin is the antimicrobial agent of choice, and macrolides are the second most common alternative. Within the last two decades, the emergence of strains of S. pneumoniae that are resistant to penicillin, macrolides, and other antimicrobial agents has become a serious health care problem (15). As of 2005, 18% of S. pneumoniae isolates in the United States were reported as penicillin resistant (9), and internationally they account for up to 60% of isolates (South Africa) (3).The rise in drug resistance of S. pneumoniae underscores the need for clinical microbiology laboratories to accurately determine its antimicrobial susceptibility profile in a timely manner. Rapid reporting of antimicrobial susceptibility test (AST) results has been shown to improve patient outcomes and to reduce hospital costs (2,10,19). To this end, automated AST systems offer the promise of shorter turnaround times to results. The literature includes reports evaluating the individual performance of each of the following AST systems for S. pneumoniae: Vitek 2, BD Phoenix, MicroScan MICroSTREP, and Etest (1,13,14,16,(20)(21)(22). However, to the best of our knowledge a cross-comparative study of all these systems has not been conducted to date. Therefore, the present study was designed to evaluate their performance and time to results (TTR).(Portions of this study were presented at the 106th General Meeting of the American Society for Microbiology, Orlando, FL, 2006, and at the 47th Interscience Conference on Antimicrobial Agents and Chemotherapy, Chicago, IL, 2007.) MATERIALS AND METHODS Test isolates.A total of 311 clinical isolates of S. pneumoniae, recovered from patients at the NewYork-Presbyterian Hospital, Columbia University Medical Center, were evaluated. All 311 strains were tested using the Phoenix, MicroScan, Etest, and PASCO reference method; 19 strains failed to grow with the Vitek 2, thus limiting the Vitek 2 evaluation to 292 clinical isolates. The specimen sources were predominately respiratory (70%), blood (12%), and eye (7%). Prior to testing, all isolates were subcultured onto BBL Columbia agar with 5% sheep blood and incubated at 35°C with 5% CO 2 for 18 to 24 h. Isolates were tested concurrently on all systems. Ma...
Rapid and accurate identification of Streptococcus pneumoniae is a critical component in the optimal management of infected patients. The performance of the BD Phoenix Automated Microbiology System (BD Diagnostic Systems, Sparks, Md.) was evaluated for identification of S. pneumoniae (n = 311) and was compared to the Vitek 2 (bioMérieux, Marcy l'Etoile, France). Strains with discordant identification between methods were resolved with 16S rRNA gene sequencing as the gold standard. The Phoenix and the Vitek 2 correctly identified 96.8% (n = 301) and 95.2% (n = 296) of S. pneumoniae strains, respectively. Overall, there was no statistically significant difference in the performance of the 2 automated systems for the identification of S. pneumoniae in this study. The Vitek 2 mean time-to-results for all streptococcal identification was 1.5 h faster than that for the Phoenix. We conclude that the automated Phoenix and the Vitek 2 systems are comparable in their ability to identify S. pneumoniae and are preferable to the use of routine biochemical assays, which have delayed time-to-results and are not dependably accurate.
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