Background: Early diagnosis and treatment are important for a good prognosis of bloodstream infections. The European Committee on Antimicrobial Susceptibility Testing (EU-CAST) recommends rapid antimicrobial susceptibility testing (RAST) based on the disk diffusion methodology for 4, 6, and 8 hours of incubation. We evaluated EUCAST-RAST of Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus from positive blood culture bottles.Methods: Twenty strains of E. coli, K. pneumoniae, and S. aureus were tested using EU-CAST-RAST. Ten antimicrobial agents against E. coli and K. pneumoniae and four agents against S. aureus were tested. The diameter of the inhibition zone (mm) was compared with the minimal inhibitory concentration (μg/mL) obtained using the Sensititre AST system (TREK Diagnostic Systems, East Grinstead, UK).Results: For E. coli, the percentage of total categorical agreement (CA) was 69.5% at 4 hours, and 87% at 8 hours. For K. pneumoniae, the total CA was 89% at 4 hours, and 95.5% at 6 hours. For S. aureus, the total CA was 100% after 4 hours. Discrepancies were observed mainly for E. coli with β-lactam antimicrobial agents, and the numbers of errors decreased over time.Conclusions: EUCAST-RAST for K. pneumoniae and S. aureus met the United States Food and Drug Administration criteria at 6 and 4 hours, respectively, whereas that for E. coli did not meet the criteria for up to 8 hours. RAST can shorten the turn-around testing time by more than one day; therefore, if applied accurately according to laboratory conditions, antimicrobial agent results can be reported faster.
tients who receive inadequate antimicrobial treatment [1]. The case fatality rate for bacteremia is 30-40% [2]. In Korea, bacteremia caused by major antimicrobial-resistant pathogens, especially among patients hospitalized in intensive care units, has a high incidence [3, 4]. Furthermore, extended-spectrum β-lactamase-producing Escherichia coli and Klebsiella pneumoniae, vancomycin-resistant Enterococcus faecium, and imipenem-resistant Acinetobacter baumannii have been on the rise [5-7]. Rapid antimicrobial susceptibility testing (AST) results are important for the selection of suitable anti-bacterial treatments for bacteremia. The main problem with current AST methods is the long turnaround time (TAT). In most cases, conducting AST requires overnight incubation and usually requires 48-72 hours to complete, depending on the drug-organism combination [8].
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