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Characterization of the Multi-Drug Resistance Gene cfr in Methicillin-Resistant Staphylococcus aureus (MRSA) Strains

Shu-Min Li1, Yu-Feng Zhou1,2, Liang Li2

  • 1Laboratory of Veterinary Pharmacology, College of Veterinary Medicine, South China Agricultural University, Guangzhou, China.

Frontiers in Microbiology
|December 13, 2018
PubMed

Insights

The cfr gene is prevalent in multidrug-resistant MRSA strains from Chinese animals and humans, often co-occurring with other resistance genes. Horizontal gene transfer via plasmids and transposons likely drives the spread of cfr-positive MRSA.

Area of Science:

  • Veterinary Microbiology
  • Antimicrobial Resistance
  • Molecular Epidemiology

Background:

  • Methicillin-resistant *Staphylococcus aureus* (MRSA) is a significant pathogen in both human and animal health.
  • The *cfr* gene confers resistance to multiple classes of antibiotics, including phenicols, lincosamides, oxazolidinones, pleuromutilins, and streptogramin A.
  • Understanding the prevalence and dissemination of *cfr*-positive MRSA is crucial for combating antimicrobial resistance.

Purpose of the Study:

  • To investigate the prevalence and characteristics of *cfr*-positive MRSA strains in China.
  • To analyze the genetic context and mobile genetic elements associated with the *cfr* gene.
  • To assess the potential for horizontal gene transfer of the *cfr* gene.

Main Methods:

  • Isolation and identification of MRSA strains from animal and human sources in China (2011-2016).
  • Antimicrobial susceptibility testing and detection of antibiotic resistance genes (ARGs).
  • Multilocus sequence typing (MLST), *spa* typing, and pulsed-field gel electrophoresis (PFGE) for molecular typing.
  • Conjugation and electroporation experiments to assess gene transferability.
  • Plasmid analysis and sequencing to determine the genetic environment of *cfr*.

Main Results:

  • Twenty *cfr*-positive MRSA strains (15.6%) were identified among 128 MRSA isolates, predominantly from food animals.
  • *cfr*-positive isolates exhibited higher resistance rates and a greater prevalence of ARGs, including co-carriage of *fexA* and *ermC*, and higher *optrA* incidence.
  • ST9 and *spa*-type t899 were the most common types, but PFGE indicated clonal diversity.
  • The *cfr* gene was successfully transferred via electroporation, with two main genetic contexts identified: a Tn*558* variant on large plasmids (∼50 kb) co-harboring *fexA*, and on small plasmids (∼7.1 kb) co-carrying *ermC*.

Conclusions:

  • Multi-drug resistance is highly prevalent in *cfr*-positive MRSA isolates from China.
  • The spread of *cfr* in MRSA appears to be driven by horizontal dissemination of *cfr*-carrying transposons and plasmids.
  • These findings highlight the importance of monitoring *cfr* in both animal and human MRSA populations to control antimicrobial resistance.
Keywords:
MRSAcfrfood animalsmulti-drug resistanceplasmid

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