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

Susan E. Flannagan, Don B. Clewell, Christine M. Sedgley

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Enterococcus faecalis MC4 harbors a 130 kb conjugative, pheromone (cCF10)-responding plasmid, pAMS1, conferring chloramphenicol, streptomycin and tetracycline resistances. A plasmid-borne class IIa bacteriocin (MC4-1) determinant and cognate immunity gene were present, but not expressed in MC4. However, pAMS1 transfer to E. faecalis JH2-2 (but not to the non-isogenic OG1SS) generated the surprising ability to express bacteriocin activity against the plasmid donor, MC4. The bacteriocin target spectrum includes E. faecalis, Enterococcus faecium, Enterococcus gallinarum, Enterococcus hirae, and Listeria monocytogenes. Those donors unable to express bacteriocin or immunity could protect themselves from the "retrocidal" behavior of transconjugants by a switch to bacteriocin resistance at a frequency of ∼10-3. Reversion to sensitivity occurred at a relatively high frequency, suggestive of involvement of a phase variation event. These observations concerning a conjugative plasmid with novel "retrocidal" properties, coupled with a defense mechanism independent of plasmid-borne immunity functions, may relate to phenomena exploiting regulatory features with broader ecological and evolutionary implications.

Original languageEnglish (US)
Pages (from-to)217-230
Number of pages14
Issue number3
StatePublished - May 2008
Externally publishedYes


  • Bacteriocin MC4-1
  • Conjugation
  • Enterococcus faecalis
  • Resistance
  • Sex pheromone
  • pAMS1

ASJC Scopus subject areas

  • Molecular Biology


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