Myungsook Kim

Background: Bacteroides fragilis is the most clinically important anaerobic bacterium and has shown increasing carbapenem resistance mediated by the cfiA metallo-β-lactamase. Although insertion sequence (IS)-mediated activation of cfiA is a well-recognized mechanism, the contribution of IS-independent genomic mechanisms remains incompletely characterized. This study investigated the phenotypic and genomic mechanisms of cfiA-associated carbapenem resistance in clinical B. fragilis isolates from Korea. Methods: Twenty-six non-duplicate carbapenem-nonsusceptible B. fragilis isolates were collected from three Korean institutions between 2022 and 2023. Antimicrobial susceptibility was tested by disk diffusion and agar dilution methods, and carbapenemase activity was assessed using the anaerobic carbapenem inactivation method (Ana-CIM) and the meropenem double-ended Etest. Whole-genome sequencing was performed to identify resistance determinants, insertion sequences, promoter structures, and multilocus sequence types. Results: Among 26 isolates, 12 (46.2%) were cfiA-positive and 14 (53.8%) were cfiA-negative. High-level resistance (imipenem MIC ≥ 32 mg/L; meropenem MIC ≥ 128 mg/L) was observed in four cfiA-positive isolates carrying activating IS elements (IS1187 or IS942) upstream of cfiA. Notably, three additional highly resistant cfiA-positive isolates lacked upstream IS elements and showed distinct genomic features, including tandem duplication of cfiA2 (SEV23_101), duplicated promoter architecture upstream of cfiA14 (SEV23_15), and high-level resistance associated with cfiA18 (SCL22_40). Ana-CIM yielded positive results only among isolates with meropenem MIC ≥ 128 mg/L, whereas the meropenem double-ended Etest failed to discriminate cfiA-associated carbapenemase activity. Conclusions: These findings indicate that high-level carbapenem resistance in B. fragilis may be associated with several genomic features, including IS-mediated activation, increased cfiA gene dosage, and promoter amplification. Molecular characterization is therefore essential for accurate interpretation of carbapenem resistance in B. fragilis.

Pasteurella multocida is an important zoonotic pathogen that causes soft-tissue infections in humans; however, recent antimicrobial susceptibility data in Korea remain limited. A total of 70 clinical P. multocida isolates collected at a nationwide commercial laboratory in Korea between November 2022 and July 2025 were analyzed. Antimicrobial susceptibility testing was performed using the disk diffusion method on Mueller-Hinton agar supplemented with 5% sheep blood. Five clinically relevant antimicrobial agents were tested: penicillin, amoxicillin-clavulanic acid (AMC), levofloxacin, tetracycline, and trimethoprim-sulfamethoxazole (TMP-SMX). For isolates classified as penicillin non-susceptible by disk diffusion, minimum inhibitory concentration (MIC) testing was performed using E-test and β-lactamase production was assessed using a phenotypic method. All tested isolates were susceptible to tetracycline and TMP-SMX by disk diffusion. Susceptibility rates by disk diffusion were 97.1% for AMC, 91.4% for levofloxacin, and 85.7% for penicillin. All 10 isolates initially classified as penicillin non-susceptible by disk diffusion were confirmed to be susceptible to penicillin by MIC testing and were β-lactamase negative. The 2 isolates classified as non-susceptible to AMC by disk diffusion were also β-lactamase negative and susceptible to penicillin by MIC testing. No β-lactam resistance was identified among the 70 clinical P. multocida isolates analyzed. These findings support current recommendations that β-lactams and other first-line agents remain active against P. multocida isolates in Korea.

Da Hye Kim, Young Geun Choi, Byeonghak Kwak, Hye Gyung Bae, Kyungwon Lee, Myungsook Kim. Korean J healthc assoc Infect Control Prev 2025;30:44-9. https://doi.org/10.14192/kjicp.2025.30.1.44

Bongyoung Kim, M.D., Ph.D., Myungsook Kim, Ph.D., Kyungwon Lee, M.D., Ph.D., and Yangsoon Lee, M.D., Ph.D.. Ann Lab Med 2025;45:223-7. https://doi.org/10.3343/alm.2024.0369

Yangsoon Lee, M.D., Ph.D., Mi-Hyun Bae, M.D., Ph.D., Hyukmin Lee, M.D., Ph.D., Myungsook Kim, Ph.D., and Kyungwon Lee, M.D., Ph.D.. Ann Lab Med -0001;0:. https://doi.org/10.3343/alm.2024.0159

Myungsook Kim. Korean J Clin Lab Sci. 2022;54:239-48. https://doi.org/10.15324/kjcls.2022.54.4.239

Myungsook Kim, Ph.D., Shin Young Yun, M.D., Yunhee Lee, B.D., Hyukmin Lee, M.D., Dongeun Yong, M.D., Kyungwon Lee, M.D.. Ann Lab Med 2022;42:188-95. https://doi.org/10.3343/alm.2022.42.2.188

Roh J, et al. Ann Lab Med. 2019 Nov;39(6):593-595. https://doi.org/10.3343/alm.2019.39.6.593

Change in Available Phosphate by Application of Phosphate Fertilizer in Long-term Fertilization Experiment for Paddy Soil-Available phosphate,Dynamics,Long-term experiment,Paddy soil