Evaluation of the Accelerate Pheno System for Identification of Acinetobacter Clinical Isolates and Minocycline Susceptibility Testing

Abstract

The Accelerate Pheno system (AXDX) is a rapid phenotypic bacterial identification and susceptibility testing system which is approved for use with positive blood cultures. Acinetobacter baumannii is a nosocomial pathogen for which the limited treatment options include minocycline in the case of multidrug resistance. Here, we studied the performance of A. baumannii identification and minocycline susceptibility testing by AXDX using 101 contemporary Acinetobacter sp. clinical isolates. Overall, the sensitivity for A. baumannii and A. baumannii complex identification was 100% (73/73) and 97.6% (82/84), respectively. Specificity for A. baumannii complex identification was 86.6% (13/15). The essential agreement of minocycline susceptibility results (±1 log2 MIC agreement) of AXDX MICs with reference broth microdilution was 98.0% (96/98). There were no very major errors or major errors. Overall, 24.5% (24/98) of results yielded minor errors. AXDX reliably identified A. baumannii and predicted minocycline susceptibility results, which should help guide treatment choices in a timely manner for infections where options are limited.

Modern Blood Culture

“…Studies using the APS assay have reported pathogen identification sensitivities ranging from 91.2% to 100% and specificities ranging from 97.3% to 100% for organisms on the panel. 45 , 48 , 49 , 50 , 51 , 52 , 53 , 54 However, 1 study reported an overall false-positive rate as high as 9.5%, of which 42.1% is mitigated by having prior negative Gram stain. 45 Therefore, confirmatory Gram stain should be performed before performing the APS assay.…”

“…Importantly, lower CA values have been observed for Pseudomonas species and Acinetobacter species. 48 , 52 , 55 Because assay performance varies depending on the pathogen, laboratories should decide on which organisms to perform the APS assay to best complement existing techniques and improve resulting times. Although this assay has high sensitivity for target organisms, in 1 study only 58.1% to 88.7% of clinical samples analyzed by this assay received any pathogen identification.…”