A multidrug resistance plasmid contains the molecular switch for type VI secretion in Acinetobacter baumannii

Proc Natl Acad Sci U S A. 2015 Jul 28;112(30):9442-7. doi: 10.1073/pnas.1502966112. Epub 2015 Jul 13.


Infections with Acinetobacter baumannii, one of the most troublesome and least studied multidrug-resistant superbugs, are increasing at alarming rates. A. baumannii encodes a type VI secretion system (T6SS), an antibacterial apparatus of Gram-negative bacteria used to kill competitors. Expression of the T6SS varies among different strains of A. baumannii, for which the regulatory mechanisms are unknown. Here, we show that several multidrug-resistant strains of A. baumannii harbor a large, self-transmissible resistance plasmid that carries the negative regulators for T6SS. T6SS activity is silenced in plasmid-containing, antibiotic-resistant cells, while part of the population undergoes frequent plasmid loss and activation of the T6SS. This activation results in T6SS-mediated killing of competing bacteria but renders A. baumannii susceptible to antibiotics. Our data show that a plasmid that has evolved to harbor antibiotic resistance genes plays a role in the differentiation of cells specialized in the elimination of competing bacteria.

Keywords: Acinetobacter baumannii; T6SS; antibiotic resistance; bacterial secretion; plasmid.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acinetobacter baumannii / genetics
  • Acinetobacter baumannii / metabolism*
  • Anti-Bacterial Agents / chemistry
  • Bacterial Secretion Systems / genetics*
  • Base Sequence
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Enzyme-Linked Immunosorbent Assay
  • Escherichia coli / metabolism
  • Microbial Sensitivity Tests
  • Molecular Sequence Data
  • Phenotype
  • Plasmids / genetics*
  • Recombinant Proteins / chemistry
  • Sequence Analysis, DNA
  • Sequence Homology, Nucleic Acid


  • Anti-Bacterial Agents
  • Bacterial Secretion Systems
  • Recombinant Proteins

Associated data

  • GENBANK/CP012004
  • GENBANK/CP012005
  • GENBANK/CP012006
  • GENBANK/CP012007
  • GENBANK/CP012008