European Committee on Antimicrobial Susceptibility Testing-Recommended Rapid Antimicrobial Susceptibility Testing of Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus From Positive Blood Culture Bottles

Abstract

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.

The Use of CHROMID® Colistin R for the Detection of Colistin-Resistant Gram-Negative Bacteria in Positive Blood Cultures

“…EUCAST has developed a rapid antimicrobial susceptibility testing method for direct testing of positive blood cultures that can generate results for Enterobacterales in as little as 4 h [ 14 , 18 ]. This is extremely useful to quickly assess whether patients with bacteraemia or sepsis are receiving optimal antimicrobial therapy.…”

“…Fonseca et al described a flow cytometry assay and applied it to simulated blood cultures spiked with 204 Gram-negative bacilli (137 Enterobacterales, 35 Pseudomonas spp. and 32 Acinetobacter baumannii ) [ 14 ]. Bacteria were extracted from positive blood cultures and incubated for 1 h at 37 °C with 2 and 4 mg/L colistin and a fluorescent dye.…”

“…Consequently, only broth microdilution is recommended by EUCAST [ 13 ]. This precludes the testing of colistin as part of EUCAST’s rapid AST method for direct testing of Gram-negative bacteria in positive blood cultures, as the method relies on disc diffusion [ 14 ].…”

Evaluation of the QMAC‐dRAST System Version 2.5 for Rapid Antimicrobial Susceptibility Testing of Gram‐Negative Bacteria From Positive Blood Culture Broth and Subcultured Colony Isolates

“…Accordingly, once the causative pathogen and its antimicrobial susceptibility are known, de‐escalation of empirical broad‐spectrum antibiotics to targeted therapy is recommended [ 6 ]. However, the slow turnaround time of conventional antimicrobial susceptibility testing (AST) methods (approximately 48–72 h from the time a blood culture turns positive) is a major bottleneck that delays the de‐escalation of empirical broad‐spectrum antibiotics to targeted antibiotics [ 7 , 8 ]. To minimize such delays, rapid AST methods that provide results within a few hours of blood culture positivity have been developed, a few of which have been approved by regulatory agencies [ 9 , 10 ].…”

Rapid Direct Identification of Microbial Pathogens and Antimicrobial Resistance Genes in Positive Blood Cultures Using a Fully Automated Multiplex PCR Assay

“… 5 6 Blood cultures (BCs) are the reference standard for diagnosing BSI. 7 However, the standard practice of BCs is time consuming because an aliquot of a positive BC must be subcultured onto solid agar plates to recover microbial isolates. 8 Species identification of positive BC isolates can be performed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).…”