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

QMAC-dRAST^TM 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).

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

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.

The high CA,% for as well GNs as GPs are promising. The presented time to report data obtained by QMAC-dRAST^TM 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.