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

• Yoo IY
• Kang OK
• Shim HJ
• Huh HJ
• Lee NY

• KMID: 2457494
• DOI: http://doi.org/10.3343/alm.2020.40.1.57

Abstract

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.

Keyword

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

MeSH Terms

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

Reference

1. Wilson P, Andrews JA, Charlesworth R, Walesby R, Singer M, Farrell DJ, et al. Linezolid resistance in clinical isolates of Staphylococcus aureus. J Antimicrob Chemother. 2003; 51:186–188. PMID: 12493812.

2. Meka VG, Pillai SK, Sakoulas G, Wennersten C, Venkataraman L, DeGirolami PC, et al. Linezolid resistance in sequential Staphylococcus aureus isolates associated with a T2500A mutation in the 23S rRNA gene and loss of a single copy of rRNA. J Infect Dis. 2004; 190:311–317. PMID: 15216466.

3. Long KS, Vester B. Resistance to linezolid caused by modifications at its binding site on the ribosome. Antimicrob Agents Chemother. 2012; 56:603–612. PMID: 22143525.

4. Hill RL, Kearns AM, Nash J, North SE, Pike R, Newson T, et al. Linezolid-resistant ST36 methicillin-resistant Staphylococcus aureus associated with prolonged linezolid treatment in two paediatric cystic fibrosis patients. J Antimicrob Chemother. 2010; 65:442–445. PMID: 20089543.

5. Locke JB, Hilgers M, Shaw KJ. Novel ribosomal mutations in Staphylococcus aureus strains identified through selection with the oxazolidinones linezolid and torezolid (TR-700). Antimicrob Agents Chemother. 2009; 53:5265–5274. PMID: 19752277.

6. Locke JB, Zuill DE, Scharn CR, Deane J, Sahm DF, Denys GA, et al. Linezolid-resistant Staphylococcus aureus strain 1128105, the first known clinical isolate possessing the cfr multidrug resistance gene. Antimicrob Agents Chemother. 2014; 58:6592–6598. PMID: 25155597.

7. Antonelli A, D'Andrea MM, Galano A, Borchi B, Brenciani A, Vaggelli G, et al. Linezolid-resistant cfr-positive MRSA, Italy. J Antimicrob Chemother. 2016; 71:2349–2351. PMID: 27073268.

8. Lee SM, Huh HJ, Song DJ, Shim HJ, Park KS, Kang CI, et al. Resistance mechanisms of linezolid-nonsusceptible enterococci in Korea: low rate of 23S rRNA mutations in Enterococcus faecium. J Med Microbiol. 2017; 66:1730–1735. PMID: 29111969.

9. CLSI. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically. CLSI M07. Wayne, PA: Clinical and Laboratory Standards Institute;2018.

10. CLSI. Performance standards for antimicrobial susceptibility testing. CLSI M100. Wayne, PA: Clinical and Laboratory Standards Institute;2018.

11. Mendes RE, Deshpande L, Streit JM, Sader HS, Castanheira M, Hogan PA, et al. ZAAPS programme results for 2016: an activity and spectrum analysis of linezolid using clinical isolates from medical centres in 42 countries. J Antimicrob Chemother. 2018; 73:1880–1887. PMID: 29659858.

12. Flamm RK, Mendes RE, Hogan PA, Streit JM, Ross JE, Jones RN. Linezolid surveillance results for the United States (LEADER surveillance Program 2014). Antimicrob Agents Chemother. 2016; 60:2273–2280. PMID: 26833165.

13. Tsiodras S, Gold HS, Sakoulas G, Eliopoulos GM, Wennersten C, Venkataraman L, et al. Linezolid resistance in a clinical isolate of Staphylococcus aureus. Lancet. 2001; 358:207–208. PMID: 11476839.

14. Baos E, Candel FJ, Merino P, Pena I, Picazo JJ. Characterization and monitoring of linezolid-resistant clinical isolates of Staphylococcus epidermidis in an intensive care unit 4 years after an outbreak of infection by cfr-mediated linezolid-resistant Staphylococcus aureus. Diagn Microbiol Infect Dis. 2013; 76:325–329. PMID: 23726146.

15. Doern CD, Park JY, Gallegos M, Alspaugh D, Burnham CA. Investigation of linezolid resistance in staphylococci and enterococci. J Clin Microbiol. 2016; 54:1289–1294. PMID: 26935728.

16. Tenover FC, Williams PP, Stocker S, Thompson A, Clark LA, Limbago B, et al. Accuracy of six antimicrobial susceptibility methods for testing linezolid against staphylococci and enterococci. J Clin Microbiol. 2007; 45:2917–2922. PMID: 17634301.