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

Abstract

Objective: QMAC-dRAST™ 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-dRAST™, such as Gram-positive bacilli, Streptococcus and Candida species. Percentages of CA (CA, %) between QMAC-dRAST™ 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-dRAST™ 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.