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Updated: Jul 7, 2026

Testing the Role of Multicopy Plasmids in the Evolution of Antibiotic Resistance
09:00

Testing the Role of Multicopy Plasmids in the Evolution of Antibiotic Resistance

Published on: May 2, 2018

A "retrocidal" plasmid in Enterococcus faecalis: passage and protection

Susan E Flannagan1, Don B Clewell, Christine M Sedgley

  • 1Cariology, Restorative Sciences and Endodontics, School of Dentistry, 1011 N. University Avenue, Ann Arbor, MI 48109-1078, USA.

Plasmid
|February 26, 2008
PubMed

Insights

A novel plasmid enables Enterococcus faecalis to produce bacteriocins against its own strain, demonstrating a unique "retrocidal" effect. This discovery offers insights into bacterial gene regulation and evolution.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Enterococcus faecalis MC4 possesses a conjugative plasmid, pAMS1, conferring antibiotic resistance.
  • The plasmid contains a bacteriocin determinant (MC4-1) and immunity gene, but these were not expressed in the original host.

Purpose of the Study:

  • To investigate the expression and function of the bacteriocin determinant on the conjugative plasmid pAMS1.
  • To understand the "retrocidal" activity observed after plasmid transfer and the host's defense mechanisms.

Main Methods:

  • Conjugative transfer of plasmid pAMS1 to different Enterococcus faecalis strains.
  • Assaying bacteriocin activity against plasmid donor and other bacterial species.
  • Determining the frequency of bacteriocin resistance and sensitivity switching.

Main Results:

  • Plasmid pAMS1 transfer induced bacteriocin expression targeting the plasmid donor (MC4) in E. faecalis JH2-2.
  • The bacteriocin exhibited a broad spectrum, including Enterococcus species and Listeria monocytogenes.
  • A plasmid-independent defense mechanism involving a switch to bacteriocin resistance was observed in susceptible strains.

Conclusions:

  • Conjugative plasmids can carry genes that confer "retrocidal" properties, impacting bacterial populations.
  • The observed defense mechanism suggests a novel, plasmid-independent strategy for bacterial self-protection.
  • These findings have implications for understanding bacterial gene regulation, plasmid evolution, and ecological dynamics.

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