Journal of global antimicrobial resistance · 2026
Fosfomycin non-susceptibility in Enterococcus faecium from Taiwan: Evaluation of testing methods and resistance determinants.
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Peng Jhih-Guang, Lin Shang-Yi, Chen Yan-Zhang, Chen Yi-Jing, Chang Chung-Yu, Hung Wei-Chun
Аннотация
BACKGROUND: Enterococcus faecium is a major cause of healthcare-associated infections and exhibits multidrug resistance. Fosfomycin, an older broad-spectrum antibiotic, has regained attention as a potential therapeutic option. However, reliable susceptibility testing remains challenging, and resistance rates and mechanisms in Taiwan are largely unexplored.
METHODS: A total of 377 E. faecium isolates from blood cultures collected in Taiwan between 2017 and 2022 were analysed. Agar dilution was used to determine fosfomycin susceptibility, which was also assessed using the E-test and disc diffusion methods. Sequence types were identified by multilocus sequence typing. Potential resistance mechanisms were examined by detecting mutations in murA and pyk genes, upstream insertions in murAB, and the presence of acquired resistance determinants.
RESULTS: Agar dilution identified 11 (2.9%) fosfomycin-resistant and 108 (29.0%) intermediate isolates. In contrast, the E-test and disc diffusion methods underestimated non-susceptibility rates (1.3% and 1.6%, respectively), primarily due to the misidentification of intermediate isolates as susceptible. Genotypic analysis of 14 fosfomycin-resistant or intermediate isolates revealed nine sequence types, with 85.7% belonging to clonal complex 17. Four MurA amino acid substitutions (A120T, I184V, R190L, and R263C) and two types of insertions upstream of murAB were detected, but none specifically correlated with resistance. All isolates tested negative for fosA, fosB, fosC, and fosX.
CONCLUSIONS: Fosfomycin resistance among E. faecium isolates in Taiwan remains low; however, intermediate isolates are frequently underestimated by the E-test and disc diffusion methods. The genetic backgrounds of fosfomycin-non-susceptible strains appear diverse, and their resistance mechanisms remain to be elucidated.
METHODS: A total of 377 E. faecium isolates from blood cultures collected in Taiwan between 2017 and 2022 were analysed. Agar dilution was used to determine fosfomycin susceptibility, which was also assessed using the E-test and disc diffusion methods. Sequence types were identified by multilocus sequence typing. Potential resistance mechanisms were examined by detecting mutations in murA and pyk genes, upstream insertions in murAB, and the presence of acquired resistance determinants.
RESULTS: Agar dilution identified 11 (2.9%) fosfomycin-resistant and 108 (29.0%) intermediate isolates. In contrast, the E-test and disc diffusion methods underestimated non-susceptibility rates (1.3% and 1.6%, respectively), primarily due to the misidentification of intermediate isolates as susceptible. Genotypic analysis of 14 fosfomycin-resistant or intermediate isolates revealed nine sequence types, with 85.7% belonging to clonal complex 17. Four MurA amino acid substitutions (A120T, I184V, R190L, and R263C) and two types of insertions upstream of murAB were detected, but none specifically correlated with resistance. All isolates tested negative for fosA, fosB, fosC, and fosX.
CONCLUSIONS: Fosfomycin resistance among E. faecium isolates in Taiwan remains low; however, intermediate isolates are frequently underestimated by the E-test and disc diffusion methods. The genetic backgrounds of fosfomycin-non-susceptible strains appear diverse, and their resistance mechanisms remain to be elucidated.