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A Small Multihost Plasmid Carrying erm(T) Identified in Enterococcus faecalis

Xing-Yun Li1, Rui Yu1, Chunyan Xu1

  • 1Department of Basic Veterinary Medicine, College of Veterinary Medicine, Henan Agricultural University, Zhengzhou, China.

Frontiers in Veterinary Science
|June 17, 2022
PubMed

Insights

Mobile genetic elements, specifically the erm(T) gene on plasmid pE165, were identified in Enterococcus faecalis. This plasmid demonstrated transmissibility to diverse bacterial hosts, conferring macrolide resistance.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Horizontal gene transfer (HGT) is a major mechanism for the spread of antimicrobial resistance.
  • The erm(T) gene confers resistance to macrolide antibiotics, including erythromycin and clindamycin.
  • Enterococcus faecalis is a significant opportunistic pathogen, and understanding its resistance mechanisms is crucial.

Purpose of the Study:

  • To identify mobile genetic elements responsible for the horizontal transfer of the erm(T) gene in Enterococcus faecalis.
  • To investigate the transmissibility of the erm(T) gene in various heterologous bacterial hosts.
  • To assess the fitness cost associated with the erm(T)-carrying plasmid in recipient strains.

Main Methods:

  • Screening of 159 erythromycin-resistant enterococci isolates for macrolide resistance genes using PCR.
  • Whole genome sequencing of the erm(T)-carrying Enterococcus faecalis E165 isolate.
  • Conjugation, natural transformation, and electrotransformation experiments to assess plasmid transmissibility.
  • Growth curve and competition experiments to evaluate fitness costs.

Main Results:

  • The erm(T) gene was detected in a single Enterococcus faecalis isolate (E165), located on a 4,244-bp plasmid designated pE165.
  • Plasmid pE165 was successfully transferred to heterologous hosts including Enterococcus faecalis, Streptococcus suis, Streptococcus mutans, and Staphylococcus aureus.
  • The erm(T)-carrying plasmid conferred erythromycin and clindamycin resistance to all tested heterologous hosts.
  • While no growth disadvantage was observed in standard growth curves, pE165-carrying recipients exhibited a fitness cost in competition experiments.

Conclusions:

  • A novel erm(T)-carrying plasmid, pE165, has been identified in Enterococcus faecalis.
  • This plasmid is transferable to a range of Gram-positive bacteria, highlighting a potential route for macrolide resistance dissemination.
  • The erm(T) gene on pE165 contributes to macrolide resistance in diverse hosts, albeit with a potential fitness cost.
Keywords:
Enterococcus faecalisclindamycinerythromycinfitness costresistancetransmission

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