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Updated: Apr 21, 2026
Isolation and Identification of Waterborne Antibiotic-Resistant Bacteria and Molecular Characterization of their Antibiotic Resistance Genes
Published on: March 3, 2023
Molecular characterization of linezolid-resistant CoNS isolates in Japan
Akiko Takaya1, Asahi Kimura1, Yoshiharu Sato1
1Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 260-8675, Japan.
Objectives:
Linezolid has been reported to remain active against 98% of staphylococci with resistance identified in 0.05% of Staphylococcus aureus and 1.4% of CoNS. The objective of this study was to characterize the linezolid-resistance mechanisms in the linezolid-resistant CoNS strains isolated in Japan.
Methods:
Staphylococcus capitis strains exhibiting linezolid MICs >8 mg/L isolated from inpatients between 2012 and 2014 were screened for cfr and mutations in 23S rRNA, L3 and L4 by PCR/sequencing. Isolates were also examined for mutations in the rlmN gene.
Results:
S. capitis had six 23S rRNA alleles. Five S. capitis isolates displayed linezolid MICs of 8, 16 and 32 mg/L. G2576U mutations were detected in three, four or five copies of 23S rRNA in all isolates. In two isolates exhibiting the highest linezolid MIC (32 mg/L) there was a large deletion in a single copy of 23S rRNA. Repeated 10 bp sequences were found in both 16S and 23S rRNAs, suggesting deletion by recombination between the repeats. One isolate had the mutation Ala-142→Thr in the ribosomal protein L3. All linezolid-resistant isolates also demonstrated mutations in the gene encoding RlmN methyltransferase, leading to Thr-62→Met and Gly-148→Ser.
Conclusions:
Multiple mechanisms appeared to be responsible for the elevated linezolid resistance in S. capitis isolates: a G2576U mutation in different numbers of copies of 23S rRNA, loss of a single copy of 23S rRNA and a mutation in the ribosomal protein L3, suggesting the accumulation of independent mutational events.
Insights
Linezolid resistance in Staphylococcus capitis is linked to multiple genetic changes. These include mutations in 23S rRNA, ribosomal protein L3, and RlmN methyltransferase, leading to elevated resistance.
Area of Science:
- Microbiology
- Molecular Biology
- Antimicrobial Resistance
Background:
- Linezolid is a crucial antibiotic for treating Gram-positive bacterial infections.
- Coagulase-negative staphylococci (CoNS) can develop resistance to linezolid, necessitating further investigation.
- Understanding resistance mechanisms is vital for preserving linezolid's efficacy.
Purpose of the Study:
- To investigate the genetic basis of linezolid resistance in CoNS strains isolated in Japan.
- To characterize the specific mutations and genetic alterations conferring resistance.
Main Methods:
- Screening of Staphylococcus capitis isolates for resistance genes (cfr) and mutations in 23S rRNA, L3, and L4.
- Utilizing PCR and sequencing to identify genetic alterations.
- Examining mutations in the rlmN gene.
Main Results:
- Identified G2576U mutations in 23S rRNA in multiple copies across all resistant isolates.
- Observed large deletions in a single copy of 23S rRNA in isolates with high-level resistance.
- Detected mutations in ribosomal protein L3 (Ala-142→Thr) and RlmN methyltransferase (Thr-62→Met, Gly-148→Ser).
Conclusions:
- Multiple genetic mechanisms contribute to elevated linezolid resistance in S. capitis.
- Accumulation of independent mutational events, including alterations in 23S rRNA, L3, and RlmN, drives resistance.
- These findings highlight the complex genetic landscape of linezolid resistance in CoNS.
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