Comparative evaluation of the STANDARD M10 and Xpert C. difficile assays for detection of toxigenic Clostridioides difficile in stool specimens.

This study compared the performance of two commercial molecular assays, the STANDARD M10 Clostridioides difficile assay (M10) and the Xpert C. difficile assay (Xpert), for detecting toxigenic C. difficile in stool specimens. A total of 487 consecutive stool specimens submitted for routine C. difficile testing between June and November 2023 were included. Following routine testing using C. DIFF QUIK CHEK COMPLETE (QCC), M10 and Xpert were tested in parallel, alongside toxigenic culture (reference standard). Additionally, two-step algorithms, using QCC on the first step and either M10 or Xpert on the second step, were assessed. Both M10 and Xpert demonstrated a sensitivity and negative predictive value (NPV) of 100%. M10 exhibited significantly higher specificity and positive predictive value (PPV; 91.9% and 64.2%, respectively) than Xpert (90.3% and 59.8%, respectively). Both two-step algorithms showed a sensitivity and NPV of 98.4% and 99.8%, respectively. The specificity and PPV of the two-step algorithm using M10 (95.2% and 75.0%, respectively) were slightly higher than those of the one using Xpert (94.8% and 73.2%, respectively), without statistical significance. Receiver operating characteristic curve analysis, assessing the predictive ability of cycle threshold (Ct) values for the detection of free toxin, exhibited an area under the curve of 0.825 for M10 and 0.843 for Xpert. This indicates the utility of Ct values as predictors for the detection of free toxin in both assays. In conclusion, M10 proves to be an effective diagnostic tool with performance comparable to Xpert, whether utilized independently or as part of a two-step algorithm.

Evaluation of the QMAC-dRAST System Version 2.5 for Rapid Antimicrobial Susceptibility Testing of Gram-Negative Bacteria From Positive Blood Culture Broth and Subcultured Colony Isolates.

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.

Antimicrobial activity of ceftazidime-avibactam against KPC-2-producing Enterobacterales: a cross-combination and dose-escalation titration study with relebactam and vaborbactam.

With the introduction of ceftazidime-avibactam worldwide, the antimicrobial activity of new ß-lactam/ß-lactamase inhibitors (BL/BLIs) needs to be investigated. From January 2020 to June 2023, Klebsiella pneumoniae carbapenemase (KPC)-producing Enterobacterales were collected. With a broth microdilution test of new BL/BLIs, cross-activity test with nine combinations of BLs and new BLIs and dose-escalation titration test for non-susceptible isolates were conducted to investigate inhibitory activities of new BLIs. A total of 188 isolates was collected and most isolates (186/188, 98.9%) carried the KPC-2 gene exclusively, while two isolates (1.1%) co-harbored NDM-1. Among the 186 KPC-2-producing isolates, 184 (98.9%) were susceptible to ceftazidime-avibactam, 173 (93.0%) to imipenem-relebactam, and 184 (98.9%) to meropenem-vaborbactam. All isolates non-susceptible to imipenem-relebactam or meropenem-vaborbactam became susceptible when avibactam replaced relebactam or vaborbactam, with 7 of 11 (63.6%) imipenem-relebactam non-susceptible isolates and both (100.0%) of the meropenem-vaborbactam non-susceptible isolates. When the minimum inhibitory concentrations (MICs) of BLs were compared using log2 scales, combinations with avibactam showed statistically significant efficacy in lowering MICs compared to relebactam and vaborbactam (all P < 0.05). In the dose-escalation test of new BLIs, increasing dose of all new BLIs corresponded to increased susceptibility to BLs. Ceftazidime-avibactam exhibited excellent susceptibility against KPC-2-producing Enterobacterales unless co-harboring metallo-ß-lactamase. The cross-combination test against non-susceptible isolates suggests that the inhibitory activity of avibactam was superior to those of relebactam or vaborbactam. Increasing the dose of new BLIs produced increased susceptibility to BLs, suggesting that high-concentration regimen need to be developed. IMPORTANCE: This study investigated 188 Klebsiella pneumoniae carbapenemase (KPC)-2-producing Enterobacterales collected from January 2020 to June 2023 in a tertiary care hospital of Korea. Most isolates were susceptible to ceftazidime-avibactam (98.9%) and meropenem-vaborbactam (98.9%), while susceptibility to imipenem-relebactam was lower (93.0%). The cross-combination test using nine combinations of the individual ß-lactams (BLs) and new ß-lactamase inhibitors (BLIs) showed that the inhibitory activity of avibactam was significantly superior to relebactam or vaborbactam when the Log2 MIC of BLs were compared for each combination with BLIs (all P < 0.05). The dose-escalation test of new BLIs demonstrated that increasing doses of new BLIs corresponded to increased susceptibility to BLs. Taken together, this study illustrates the excellent activity of ceftazidime-avibactam against KPC-2-producing Enterobacterales and suggests further investigation into high-concentration regimens for potentially non-susceptible clinical isolates.

Communication: Evaluation of the Humasis COVID-19 Antigen Rapid Diagnostic Test for the Diagnosis of SARS-CoV-2 Infection.

OBJECTIVE: We assessed the performance of the Humasis COVID-19 AgHS Test (Humasis, Korea), a novel antigen rapid diagnostic test (Ag-RDT) based on lateral flow immunoassay. METHODS: 85 SARS-CoV-2-positive and 155 SARS-CoV-2-negative nasopharyngeal swab specimens confirmed by rRT-PCR were tested using the Humasis and PBCheck Ag-RDTs. The analytical specificity of the Humasis Ag-RDT was evaluated using 27 strains of human respiratory pathogens. RESULTS: The overall sensitivity and specificity were 72.9% and 99.4% for the Humasis Ag-RDT and 64.7% and 100% for the PBCheck Ag-RDT, respectively. The sensitivity for specimens with Ct≤25 was 100% for both Ag-RDTs. The Humasis Ag-RDT showed no cross-reactivity with other respiratory pathogens. CONCLUSION: Our data suggests that the Humasis Ag-RDT can be a useful diagnostic tool for the detection of SARS-CoV-2 infection.

Performance evaluation of the SMG HHV-6 Q Real-Time PCR Kit for quantitative detection and differentiation of human herpesvirus 6A and 6B.

The aim of this study was to compare the performance of the newly developed SMG HHV-6 Q Real-Time PCR Kit (SMG assay) with the RealStar HHV-6 PCR Kit (RealStar assay). The analytical sensitivity and specificity, linearity, and precision of the SMG assay were evaluated. The clinical performance of the SMG assay was assessed and compared with that of the RealStar assay using 207 clinical specimens (HHV-6A positive, n = 51; HHV-6B positive, n = 64; HHV-6A/B negative, n = 92). The limit of detection of the SMG assay was 2.92 log10 copies/mL for HHV-6A DNA and 2.88 log10 copies/mL for HHV-6B DNA. The linear range was determined to be 3.40-9.00 log10 copies/mL for both viruses. Intra- and inter-assay variability were below 5% at concentrations ranging from 4 to 9 log10 copies/mL. No cross-reactivity was observed with the 25 microorganisms included in the specificity panel. The clinical sensitivity and specificity of the SMG and RealStar assays compared to in-house polymerase chain reaction and sequencing were as follows: SMG assay, 98.0% and 100% for HHV-6A DNA, respectively, and 96.9% and 100% for HHV-6B DNA, respectively; RealStar assay, 98.0% and 100% for HHV-6A DNA, respectively, and 90.6% and 100% for HHV-6B DNA, respectively. The correlation coefficients between viral loads measured by the two assays were 0.948 and 0.975, with mean differences of 0.62 and 0.32 log10 copies/mL for HHV-6A and HHV-6B DNA, respectively. These results demonstrate that the SMG assay is a sensitive and reliable tool for the quantitative detection and differentiation of HHV-6A and HHV-6B DNA.IMPORTANCEQuantitative real-time PCR (qPCR) that can distinguish between HHV-6A and HHV-6B DNA is recommended for diagnosis of active infection. The SMG HHV-6 Q Real-Time PCR Kit (SMG assay) is a newly developed qPCR assay that can differentiate between HHV-6A and HHV-6B DNA; however, little is known about its performance. In this study, we assessed the performance of the SMG assay and compared it with that of a commercially available qPCR assay, the RealStar HHV-6 PCR Kit (RealStar assay). The SMG assay demonstrated excellent analytical sensitivity and specificity, precision, and linearity. Furthermore, the viral loads measured by the SMG assay were highly correlated with those measured by the RealStar assay. Our results suggest that the SMG assay is a useful diagnostic tool for quantitative detection and differentiation of HHV-6A and HHV-6B DNA.

No Significant Differences in Presepsin Levels According to the Causative Microorganism of Bloodstream Infection.

BACKGROUND: CD14 recognizes lipopolysaccharide (LPS), and presepsin is a fragment of soluble CD14. Still, it remains uncertain whether Gram-negative bacteria induce higher presepsin levels than other microorganisms. To address this question, this study aimed to analyze presepsin levels based on microorganisms isolated in blood cultures. MATERIALS AND METHODS: This study was a single-center study comprising suspected sepsis patients enrolled from July 2020 to September 2020. A total of 95 patients with a single isolate confirmed in blood culture were analyzed to evaluate if there are any differences in presepsin levels according to microbial isolates. Plasma presepsin level was measured using PATHFAST assay kit and analyzer (LSI Medience Corporation, Tokyo, Japan). RESULTS: There were 26 Gram-positive bacteremia, 65 Gram-negative bacteremia, and 3 fungemia patients with median presepsin levels of 869, 1,439, and 11,951 pg/mL, respectively. Besides, one case of algaemia demonstrated a presepsin level of 1,231 pg/mL. Our results showed no statistically significant difference in presepsin levels among patients with Gram-positive bacteremia, Gram-negative bacteremia, and fungemia. Furthermore, presepsin levels did not differ significantly among bloodstream infections caused by bacteria that were isolated from at least three different patients. In particular, Gram-positive bacteria such as Staphylococcus aureus and Enterococcus faecalis were able to induce presepsin levels comparable to those induced by Gram-negative bacteria. CONCLUSION: We demonstrated that there were no significant differences in plasma presepsin levels according to microbial isolates in blood culture. The major cause of the variability in presepsin levels during bloodstream infection might be the immunogenicity of each microorganism rather than the presence of LPS in the microorganism.