Evaluation of the Alfred AST® system for rapid antimicrobial susceptibility testing directly from positive blood cultures
To assess the concordance of antimicrobial susceptibility testing results obtained by the Alfred AST® system performed directly from positive blood cultures in comparison with the standard susceptibility test results performed from isolated colonies by an automated broth microdilution method and to determine the applicability of Alfred AST® system in the routine of our blood culture laboratory. This system is based on the detection of growth by turbidimetry through a technology based on light scattering. Antimicrobial susceptibility testing was performed directly from positive bottles by the Alfred AST® system (Alifax, Padova, Italy). The broth microdilution method (MicroScan, Beckman Coulter, CA, USA) performed to the isolates was considered the standard for comparison. We evaluated 115 significant episodes of bacteremia produced by 51 Gram-negative Enterobacterales, 8 Pseudomonas spp., 2 non-fermenting Gram-negative rods, 7 Staphylococcus aureus, 23 coagulase-negative Staphylococcus, 12 Enterococcus spp., and 12 Streptococcus spp. We performed 828 susceptibility determinations with a categorical agreement with the standard method of 97.1%. Only 24 errors (2.9%) were detected. It should be pointed out that for staphylococci and glycopeptides the correlation was only 87% and for non-fermenting Gram-negative rods and piperacillin/tazobactam was only 88.9%. Time to get antibiogram results by Alfred AST® system was 5 versus 48 h for the standard microdilution method from the isolated colonies. The Alfred AST® system is a useful and rapid method to obtain antimicrobial susceptibility results within the same work shift after blood culture positivity.
KeywordsBlood cultures Rapid antimicrobial testing Sepsis Bactec FX Bacteremia Alfred 60AST
This work was presented in part at the XX Congreso de la Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica (SEIMC), May 2016, Barcelona, Spain.
Compliance with ethical standards
Conflict of interest
The authors declare that they do not have conflicts of interest.
Informed consent was obtained from all individual participants included in the study.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
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