RESEARCH ARTICLE


Performance of QMAC-dRASTTM (Direct Rapid Antimicrobial Susceptibility Testing) - a Newcomer in Phenotypic Automatic AST



Jens J. Christensen1, 2, *, Hanne Junker1, Connie B. Madsen1, Camilla F. Christiansen1, Tina Kristensen1, Tine K. Lund1, Majbritt Fallesen1, Rie Kjølsen1, Bodil Hansen1, Pia K. Hansen1, Ulrich S. Jensen1
1 The Regional Department of Clinical Microbiology, Zealand University Hospital, Ingemannsvej 46, 4200 Slagelse, Denmark
2 Institute of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark


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Creative Commons License
© 2021 Christensen et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at Department of Clinical Microbiology, Zealand University Hospital, Ingemannsvej 46, 4200 Slagelse, Denmark;
Tel: +4558559404; E-mail: jejc@regionsjaelland.dk.


Abstract

Objective:

QMAC-dRASTTM is a phenotypic automatized Antibiotic Susceptibility Testing (AST) system based on microfluidic chip technology enabling observation of changes in a single bacterial cell under antibiotic treatment conditions. The 96 wells plate with dried antibiotics comprises 19 and 17 antibiotics for the Gram-Negatives (GNs) and Gram-Positives (GPs), respectively. Categorical (Sensitive, Intermediate or Resistant) results were compared to results obtained by our laboratory standard susceptibility testing procedure and given as Categorical Agreement (CA).

Methods:

In a 3-month period (2019/2020), blood cultures detected positive were included. Excluded were known off-panel strains of QMAC-dRASTTM, such as Gram-positive bacilli, Streptococcus and Candida species. Percentages of CA (CA, %) between QMAC-dRASTTM and routine testing methods used in the laboratory (EUCAST disc diffusion and/or etest/Broth Micro Dilution MIC), were calculated.

Results:

255 positive blood cultures from as many patients were examined. Of the positive blood culture strains, 144 were GNs, and 111 were GPs. An overall combined CA,% of 96.3 (2410 of 2502 determinations) was obtained, and discrepancies were noted in 92 of 2502 test results (3.7%). The percentage of very major errors (VMEs) was 0.7% for GNs and 2.2% for GPs. For 87% of blood culture specimens examined, susceptibility reports were available within 6-7 hours.

Conclusion:

The high CA,% for as well GNs as GPs are promising. The presented time to report data obtained by QMAC-dRASTTM in this study being of 3-8 hours for blood culture specimens examined strongly support a further possible improvement in the workflow for handling blood stream infections.

Keywords: Quantamatrix-direct, Rapid, Antimicrobial Susceptibility Testing (QMAC-dRASTTM), Blood Stream Infection, Antibiotic Susceptibility Testing (AST), Phenotypic AST testing.