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BACKGROUND: Rapid antimicrobial susceptibility testing (AST) for bloodstream infections (BSIs) facilitates the optimization of antimicrobial therapy, preventing antimicrobial resistance and improving patient outcomes. QMAC-dRAST (QuantaMatrix Inc., Korea) is a rapid AST platform based on microfluidic chip technology that performs AST directly using positive blood culture broth (PBCB). This study evaluated the performance of QMAC-dRAST for Gram-negative bacteria using PBCB and subcultured colony isolates, comparing it with that of VITEK 2 (bioMérieux, France) using broth microdilution (BMD) as the reference method. METHODS: We included 141 Gram-negative blood culture isolates from patients with BSI and 12 carbapenemase-producing clinical isolates of Enterobacterales spiked into blood culture bottles. QMAC-dRAST performance was evaluated using PBCB and colony isolates, whereas VITEK 2 and BMD were tested only on colony isolates. RESULTS: For PBCB, QMAC-dRAST achieved 92.1% categorical agreement (CA), 95.3% essential agreement (EA), with 1.8% very major errors (VMEs), 3.5% major errors (MEs), and 5.2% minor errors (mEs). With colony isolates, it exhibited 92.5% CA and 95.1% EA, with 2.0% VMEs, 3.2% MEs, and 4.8% mEs. VITEK 2 showed 94.1% CA and 96.0% EA, with 4.3% VMEs, 0.4% MEs, and 4.3% mEs. QMAC-dRAST yielded elevated error rates for specific antimicrobial agents, with high VMEs for carbapenems and aminoglycosides. The median time to result for QMAC-dRAST was 5.9 h for PBCB samples and 6.1 h for subcultured colony isolates. CONCLUSIONS: The QMAC-dRAST system demonstrated considerable strengths and comparable performance to the VITEK 2 system; however, challenges were discerned with specific antimicrobial agents, underlining a necessity for improvement.

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BACKGROUND: Rapid and accurate identification of nontuberculous mycobacteria (NTM) species is essential for the diagnosis and treatment of NTM disease. MolecuTech REBA Myco-ID (YD Diagnostics, Yongin, Korea) is a line probe assay for identification of NTM species and can be performed using HybREAD480, an instrument for automating the post-PCR steps. In this study, we assessed the performance of MolecuTech REBA Myco-ID using HybREAD480. METHODS: Seventy-four reference strains, including 65 Mycobacterium strains and nine non-Mycobacterium strains within the order Mycobacteriales, were used to determine the analytical specificity of MolecuTech REBA Myco-ID. The clinical performance of this assay was evaluated with 192 clinical Mycobacterium strains, and the assay results were compared to those of multigene sequencing-based typing. RESULTS: The accuracy of MolecuTech REBA Myco-ID for the 74 reference strains and 192 clinical strains was 77.0% (57/74; 95% confidence interval [CI], 65.8 - 86.0%) and 94.3% (181/192; 95% CI, 90.0 - 97.1%), respectively. Although some rarely isolated NTM species are misidentified, the most commonly isolated NTM species, including M. avium complex, M. abscessus subsp. abscessus, M. abscessus subsp. massiliense, and M. fortuitum com-plex, were all correctly identified. Of note, all M. lentiflavum strains tested (reference strain, n = 1; clinical strain, n = 10) were misidentified as M. gordonae. CONCLUSIONS: MolecuTech REBA Myco-ID using HybREAD480 was accurate for identifying commonly isolated NTM species and for discriminating between M. abscessus subsp. abscessus and M. abscessus subsp. massiliense. However, the main limitations of this assay, including misidentification of some rarely isolated NTM species and cross-reactivity between M. lentiflavum and M. gordonae, should be considered.

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We evaluated the GenoType NTM-DR (NTM-DR) line probe assay for identifying Mycobacterium avium complex (MAC) species and Mycobacterium abscessus subspecies and for determining clarithromycin and amikacin resistance. Thirty-eight reference strains and 145 clinical isolates (58 MAC and 87 M. abscessus isolates), including 54 clarithromycin- and/or amikacin-resistant strains, were involved. The performance of the NTM-DR assay in rapid identification was evaluated by comparison with results of multigene sequence-based typing, whereas performance in rapid detection of clarithromycin and amikacin resistance was evaluated by comparison with sequencing of the erm(41), rrl, and rrs genes and drug susceptibility testing (DST). The accuracies of MAC and M. abscessus (sub)species identification were 92.1% (35/38) and 100% (145/145) for the 38 reference strains and 145 clinical isolates, respectively. Three MAC strains other than M. intracellulare were found to cross-react with the M. intracellulare probe in the assay. Regarding clarithromycin resistance, NTM-DR detected rrl mutations in 52 isolates and yielded 99.3% (144/145) and 98.6% (143/145) concordant results with sequencing and DST, respectively. NTM-DR sensitivity and specificity in the detection of clarithromycin resistance were 96.3% (52/54) and 100% (91/91), respectively. The NTM-DR yielded accurate erm(41) genotype results for all 87 M. abscessus isolates. Regarding amikacin resistance, NTM-DR detected rrs mutations in five isolates and yielded 99.3% (144/145) and 97.9% (142/145) concordant results with sequencing and DST, respectively. Our results indicate that the NTM-DR assay is a straightforward and accurate approach for discriminating MAC and M. abscessus (sub)species and for detecting clarithromycin and amikacin resistance mutations and that it is a useful tool in the clinical setting.

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BACKGROUND: The AdvanSure MDR-TB GenoBlot Assay detects isoniazid- and rifampin-resistant tuberculosis using mutation-specific probes, including probes to disputed rpoB mutations. The aim of this study was to evaluate the clinical usefulness of molecular drug susceptibility testing (DST) using the AdvanSure assay with weekly batch testing in routine clinical laboratory settings in a country with an intermediate tuberculosis burden. METHODS: The AdvanSure assay was evaluated against an absolute concentration (AC) method and the Mycobacterial Growth Indicator Tube (MGIT) 960 System, which are phenotypic DST methods, using 496 Mycobacterium tuberculosis (MTB) isolates. We retrospectively reviewed and compared DST results and turnaround times (TATs), the time intervals from MTB culture identification to final reporting, for these methods. RESULTS: For rifampin, the AdvanSure assay showed 99.2% (492/496) concordance with both the AC and MGIT methods. AdvanSure also detected an rpoB mutation (D516Y) conferring low-level resistance in three isolates categorized as rifampin-susceptible by both phenotypic DST methods. For isoniazid, AdvanSure concordance rates with the AC method and MGIT DST were 96.6% (479/496) and 95.4% (473/496), respectively. The median TAT of AdvanSure in weekly batch testing was 5.8 days, shorter than the times for the phenotypic DST methods, which were 35.1 days for the AC method and 8.9 days for MGIT DST. CONCLUSIONS: AdvanSure shows promising clinical usefulness for rapid detection of rifampin- and/or isoniazid-resistant tuberculosis when used as a complementary method to phenotypic DST assays in weekly batch testing. Furthermore, MTB isolates with disputed mutations for rifampin resistance were detectable by the AdvanSure assay.

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