Identification and antimicrobial susceptibility testing of clinical isolates of nonfermenting gram-negative bacteria by the Phoenix Automated Microbiology System.

The Phoenix Automated Microbiology System (Becton Dickinson, Sparks, MD) was evaluated for its ability to identify nonfermenting gram-negative pathogens and measure their drug susceptibility. Isolates producing rare extended-spectrum β-lactamases (PER-1, IMP-2, VIM-1, and VIM-2) were included in the study. Species identification was compared to that given by the ATB System (bio-Merieux, Marcy l'Etoile, France), whereas susceptibility results were compared to those produced by a reference broth microdilution test (panels manufactured by Pasco Laboratories, Becton Dickinson). The Phoenix system consistently identified all isolates of Pseudomonas aeruginosa (n=55) and Stenotrophomonas maltophilia (n=28), while in other cases species agreement was obtained for 47/53 isolates (Acinetobacter baumannii, 29/31; Pseudomonas putida, 10/11; Burkholderia cepacia, 6/7; and Pseudomonas fluorescens, 2/4). Overall, the Phoenix and ATB systems gave equal results in 130/136 cases (95.6%). For two isolates, consistent identification was obtained at the genus level, thus bringing the cumulative agreement to 97.1%. MIC values (interpreted according to NCCLS guidelines) gave essential and categorical agreement in 94.2% and 93.1% of cases, respectively. Minor and major errors were 5.1% and 5.2%, respectively. No very major errors were produced. The mean time to results (TTR) for the Phoenix system was 14.8 ± 1.6 h (mean ± SD), with the shortest TTR being observed for A. baumannii (13.0 ± 1.8 h) and the longest one for P. aeruginosa (15.6 ± 1.2 h). In conclusion, the Phoenix system performed rapidly and correctly in the identification of clinical isolates of important opportunistic pathogens and in measuring their susceptibility to antipseudomonal drugs.