Résumé
Background@#Rapid antimicrobial susceptibility testing (RAST) is important for the appropriate treatment of bloodstream infections. The QMAC-dRAST system (QuantaMatrix Inc., Korea) can directly perform RAST using positive blood culture samples with microscopic imaging. This study aimed to evaluate the performance of the QMAC-dRAST system for AmpCβ-lactamase-producing Enterobacterales. @*Methods@#Eighty isolates (20 Morganella morganii, 20 Serratia marcescens, 10 Klebsiella aerogenes, 10 Enterobacter cloacae, and 20 Citrobacter freundii) and 14 antimicrobial agents were included in the antimicrobial susceptibility testing (AST). The performance of the QMAC-dRAST system was evaluated by simulating the clinical blood culturing process. We conducted a comparative evaluation of the QMAC-dRAST and Vitek 2 systems (bioMérieux Inc., France). Broth microdilution tests were performed as the reference method to resolve any discrepancies in the AST results between the two systems. @*Results@#For 20 M. morganii and 20 S. marcescens, the categorical agreement (CA) between the QMAC-dRAST and Vitek 2 systems increased from 55.4% to 83.8% after AST algorithm optimization. Moreover, the discrepancy rates decreased as follows: from 19.1% to 5.4% very major errors (VME), from 38.3% to 4.3% major errors (ME), and from 14.6% to 12.1% minor errors (mE) for the QMAC-dRAST system compared to the Vitek 2 system. For all 80 tested isolates, the QMAC-dRAST system showed 93.0% CA, 1.7% VME, 2.3% ME, and 4.9% mE. @*Conclusion@#The QMAC-dRAST system was comparable to the Vitek 2 system after AST algorithm optimization for AmpC β-lactamase-producers, which are major pathogens and require time to express the enzyme. However, further modifications of the AST algorithm are still warranted.
Résumé
Background@#The rapid antimicrobial susceptibility testing (AST) performed on urine samples would guide the adequate choice of antibiotics for obtaining better treatment outcomes in patients. Our study aimed to evaluate the performance of the modified-EUCAST (European Committee on Antimicrobial Susceptibility Testing) rapid direct AST on urine samples. @*Methods@#From >2,000 urine samples, a total of 128 urine samples containing bacterial counts of ≥2 × 10 4 CFU/mL with a uniform bacterial shape were initially included based on flow cytometry (Sysmex UF-1000i, Japan) and Gram staining, respectively. A total of 103 samples showing the presence of Enterobacteriaceae were finally selected in this study. The urine samples were directly inoculated on Mueller-Hinton agar, which was used in the current EUCAST rapid direct AST on blood samples. The size of the growth inhibition zones around antimicrobial disks was measured using a digital scanner (BIOMIC vision analyzer, Giles scientific, USA) and further confirmed by visualization with naked eyes after incubation for 4, 6, and 8 hours. The AST interpretations were compared to those of the conventional VITEK 2 AST system (bioMérieux, France) and the discrepancies between both tests were confirmed with the E-test. @*Results@#The antibiotics, namely ampicillin, cefazolin, aztreonam, ceftazidime, cefotaxime, cefoxitin, cefepime, gentamicin, ciprofloxacin, and cotrimoxazole showed excellent correlations with modified-EUCAST rapid direct test and conventional ASTs with >0.75 weighted kappa values. The categorical agreement of the rapid direct AST was 1,442 (93.3%), with 76 (4.9%) minor error, 9 (0.6%) major error and 18 (1.2%) very major error, implicating the reliability of this method for clinical application. @*Conclusion@#Performing the modified-EUCAST rapid direct AST on urine samples can predict reliable AST results within 8 hours. The rapid direct AST can help the physicians to initiate adequate antimicrobial treatment for urinary tract infections.