Antibiotics (Nov 2022)

Prevalence and Genetic Analysis of Resistance Mechanisms of Linezolid-Nonsusceptible Enterococci in a Tertiary Care Hospital Examined via Whole-Genome Sequencing

  • Yuxin Hu,
  • Dongju Won,
  • Le Phuong Nguyen,
  • Kennedy Mensah Osei,
  • Younghee Seo,
  • Junglim Kim,
  • Yoonhee Lee,
  • Hyukmin Lee,
  • Dongeun Yong,
  • Jong Rak Choi,
  • Kyungwon Lee

DOI
https://doi.org/10.3390/antibiotics11111624
Journal volume & issue
Vol. 11, no. 11
p. 1624

Abstract

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(1) Background: Linezolid plays an important role in the treatment of invasive infections caused by vancomycin-resistant enterococci after its introduction to clinical practice. However, a detailed examination of linezolid-nonsusceptible enterococci (LNSE) is required. In this study, we attempted to analyze the mechanisms of LNSE strains isolated from a tertiary care hospital. (2) Methods: From 2019 to 2020, 18 Enterococcus faecalis, 14 E. faecium, and 2 E. gallinarum clinical isolates were collected at Severance Hospital. Agar dilution was performed to evaluate precise linezolid minimum inhibitory concentrations (MICs). Short-read whole-genome sequencing (WGS) was used to analyze resistance determinants. (3) Results: The presence of the optrA gene was likely the primary resistance mechanism in these three species, typically demonstrating a MIC value of 8 μg/mL. The co-existence of the cfr(D) and poxtA2 gene was the second major mechanism, primarily predicting a phenotype showing intermediate susceptibility to linezolid. G2576U mutation on 23S rRNA was only found in E. faecium; it mediated the most significant increase in linezolid MIC. (4) Conclusion: This is the first report examining poxtA2–cfr(D) co-harboring clinical enterococcal isolates in Korea and demonstrating the poxtA EF9F6-harboring clinical E. gallinarum strain worldwide. The comparison with resistance-gene-containing fragments in the isolates obtained from different countries and different sources demonstrated the spread of linezolid-resistance genes and suggested the possibility of foodborne transmission.

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