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...
