Methicillin-resistant Staphylococcus aureus (MRSA) is a serious pathogen in clinical settings and early detection is critical. Here, we investigated the MRSA discrimination potential of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) using 320 clinical S. aureus isolates obtained in 2005–2014 and 181 isolates obtained in 2018. We conducted polymerase chain reactions (PCR) for staphylococcal cassette chromosome mec (SCCmec) typing and MALDI-TOF MS to find specific markers for methicillin resistance. We identified 21 peaks with significant differences between MRSA and methicillin-susceptible S. aureus (MSSA), as determined by mecA and SCCmec types. Each specific peak was sufficient to discriminate MRSA. We developed two methods for simple discrimination according to these peaks. First, a decision tree for MRSA based on six MRSA-specific peaks, three MSSA-specific peaks, and two SCCmec type IV peaks showed a sensitivity of 96.5%. Second, simple discrimination based on four MRSA-specific peaks and one MSSA peak had a maximum sensitivity of 88.3%. The decision tree applied to 181 S. aureus isolates from 2018 had a sensitivity of 87.6%. In conclusion, we used specific peaks to develop sensitive MRSA identification methods. This rapid and easy MALDI-TOF MS approach can improve patient management.

Background and objectives: The ABO antibody (Ab) titration tests are used in monitoring in ABO-incompatible (ABOi) solid organ transplantation (SOT). However, currently developed ABO Ab tests show Ab binding reactions. This study attempted to measure ABO Ab level using complement-dependent cytotoxicity (CDC). Materials and methods: We studied 93 blood group O serum samples from patients who underwent ABOi SOT from January 2019 to May 2021. Patients’ sera were incubated with A1 or B cells and added to a human complement solution. Supernatants were collected after centrifugation, and free hemoglobin (Hb) was measured by spectrophotometry. We converted plasma Hb value to hemolysis (%), which were compared with ABO Ab titer. Results: We found a mild correlation between hemolysis and ABO Ab titers. In simple regression analysis, the correlation coefficients were within 0.3660–0.4968 (p < 0.0001) before transplantation. In multiple linear regression analysis, anti-A hemolysis (%) was higher in immunoglobulin M (IgM) (β = 12.9) than in immunoglobulin G (IgG) (β = −3.4) (R2 = 0.5216). Anti-B hemolysis was higher in IgM (β = 8.7) than in IgG (β = 0.0) (R2 = 0.5114). There was a large variation in hemolysis within the same Ab titer. Conclusions: CDC can be used in a new trial for ABO Ab measurement. Furthermore, IgM rather than IgG seems to play a significant role in vivo activity, consistent with previous knowledge. Thus, this study may help in the development of the ABO Ab titration supplement test for post-transplant treatment policy establishment and pre-transplant desensitization.

Background: Microsatellite instability (MSI) is an important biomarker for the diagnosis of Lynch syndrome and for guiding immunotherapy in various solid tumors. Droplet digital PCR (ddPCR) has emerged as a highly sensitive method for detecting MSI, particularly in circulating tumor DNA (ctDNA). This study aimed to evaluate the analytical and clinical performance of a ddPCR assay using three MSI markers (BAT-26, ACVR2A, and DEFB105A/B) in colorectal, gastric, and endometrial cancers. Methods: Formalin-fixed paraffin-embedded (FFPE) samples from 190 patients (83 colorectal, 44 gastric, and 63 endometrial cancers) and 21 plasma samples from patients with metastatic solid tumors were analyzed. MSI status determined by ddPCR was compared with conventional PCR using a pentaplex panel and immunohistochemistry (IHC). Analytical performance, including limit of blank (LoB) and limit of detection (LoD), was evaluated using cell line DNA, and clinical cut-offs were established using receiver operating characteristic analysis. Results: The ddPCR assay demonstrated high analytical sensitivity, with LoD values of 0.075% for BAT-26, 0.1% for ACVR2A, and 0.025% for DEFB105A/B. Using optimized clinical cut-offs, the concordance rate between ddPCR and conventional PCR assays was 98.4% in tissue samples. Marker performance varied by cancer type, with reduced sensitivity observed in endometrial cancer. In plasma samples, MSI-H was detected in 1 of 21 cases (4.8%), and the overall concordance rate with tissue-based MSI status was 94.7%. Conclusions: The ddPCR assay demonstrated high concordance with conventional MSI testing methods and showed potential as a sensitive tool for MSI detection in both tissue and plasma samples. However, optimization of marker panels and establishment of sample-type-specific clinical cut-offs are required, particularly for ctDNA-based analysis. Further large-scale studies are needed to validate the clinical utility of ddPCR for MSI detection and monitoring.