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

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

Author information

1
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2G2; Department of Molecular Microbiology, Washington University School of Medicine in St. Louis, St. Louis, MO 63110;
2
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2G2;
3
Department of Medical Microbiology and Immunology, Heritage Medical Research Center, University of Alberta, Edmonton, AB, Canada T6G 2S2.
4
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2G2; Department of Molecular Microbiology, Washington University School of Medicine in St. Louis, St. Louis, MO 63110; mariofeldman@wustl.edu.

Abstract

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

PMID:
26170289
PMCID:
PMC4522760
DOI:
10.1073/pnas.1502966112
[Indexed for MEDLINE]
Free PMC Article

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