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The fosfomycin resistance gene fosB3 is located on a transferable, extrachromosomal circular intermediate in clinical

Xiaogang Xu1, Chunhui Chen, Dongfang Lin

  • 1Institute of Antibiotics, Huashan Hospital, Fudan University, Shanghai, China ; Key Laboratory of Clinical Pharmacology of Antibiotics, Ministry of Health, China.

Plos One
|November 9, 2013
PubMed

Insights

Vancomycin-resistant Enterococcus faecium isolates exhibit fosfomycin resistance due to a transferable fosB3 gene. This gene confers high-level fosfomycin resistance in both Gram-positive and Gram-negative bacteria.

Area of Science:

  • Microbiology
  • Genetics
  • Antimicrobial Resistance

Background:

  • Vancomycin-resistant Enterococcus faecium (VREfm) is a significant healthcare-associated pathogen.
  • Some VREfm isolates co-harbor resistance to other antibiotics, including fosfomycin.
  • The emergence of fosfomycin resistance in VREfm necessitates understanding its underlying mechanisms.

Purpose of the Study:

  • To investigate the genetic basis of fosfomycin resistance in clinical VREfm isolates from China.
  • To characterize the mechanism and transferability of the identified fosfomycin resistance determinant.

Main Methods:

  • Antimicrobial susceptibility testing (MIC determination).
  • Bacterial conjugation (filter-mating) for gene transfer studies.
  • Next-generation sequencing (Illumina/Solexa) and inverse PCR for gene identification.
  • Gene cloning and transformation into E. coli for functional analysis.

Main Results:

  • Three VREfm clinical isolates displayed high-level resistance to both vancomycin (>256 µg/ml) and fosfomycin (>1024 µg/ml).
  • Resistance determinants were co-transferred via conjugation, indicating a common genetic element.
  • A novel fosfomycin resistance gene, designated fosB3, was identified, differing slightly from known staphylococcal fosB genes.
  • Cloning and expression of fosB3 in E. coli resulted in a 750-fold increase in fosfomycin MIC.
  • The fosB3 gene was found to be located on a transferable extrachromosomal circular intermediate.

Conclusions:

  • The fosB3 gene is responsible for high-level fosfomycin resistance in the studied VREfm isolates.
  • fosB3 is a transferable gene that can confer fosfomycin resistance in both Gram-positive and Gram-negative bacteria.
  • The presence of fosB3 on a mobile genetic element poses a significant threat for the dissemination of fosfomycin resistance.

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