Ann Lab Med.  2020 Jan;40(1):57-62. 10.3343/alm.2020.40.1.57.

Linezolid Resistance in Methicillin-Resistant Staphylococcus aureus in Korea: High Rate of False Resistance to Linezolid by the VITEK 2 System

  • 1Department of Laboratory Medicine and Genetics, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.,
  • 2Center for Clinical Medicine, Samsung Biomedical Research Institute, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.


As various linezolid resistance mechanisms have been identified in methicillin-resistant Staphylococcus aureus (MRSA), we investigated the molecular characteristics of MRSA with elevated linezolid minimum inhibitory concentrations (MICs), using the VITEK 2 system (bioMérieux, Marcy-l'Étoile, France). Twenty-seven MRSA isolates from 14 patients exhibiting linezolid MICs ≥8 µg/mL were examined by broth microdilution (BMD) test as well as by sequencing for mutations in the 23S rRNA gene or ribosomal proteins (L3, L4, and L22) and the presence of the optrA, cfr, and cfr(B) genes. Of the 27 isolates, four (14.8%) from one patient were confirmed as linezolid resistant by BMD and harbored a 23S rRNA T2500A mutation. The remaining 23 were confirmed as linezolid susceptible, indicating that the linezolid-resistant results were major errors generated by VITEK 2. The most commonly detected mutation (19/27, 70.4%), L3 Gly152Asp, was detected in only linezolid-susceptible isolates. No isolates contained optrA, cfr, or cfr(B) or any L4 or L22 protein alterations. Our results show that the 23S rRNA T2500A mutation was mainly associated with linezolid resistance, while the L3 Gly152Asp mutation was not related to linezolid resistance. A confirmatory test is recommended for VITEK 2 linezolid-resistant results owing to the high probability of false resistant results.


Methicillin-resistant Staphylococcus aureus; Linezolid; Resistance; 23S ribosomal RNA; VITEK 2

MeSH Terms

Genes, rRNA
Methicillin Resistance*
Methicillin-Resistant Staphylococcus aureus*
Microbial Sensitivity Tests
Ribosomal Proteins
RNA, Ribosomal, 23S
RNA, Ribosomal, 23S
Ribosomal Proteins


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