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Updated: Aug 10, 2026

Characterizing Multidrug Efflux Systems in Acinetobacter baumannii Using an Efflux-Deficient Bacterial Strain and a Single-Copy Gene Expression System
05:06

Characterizing Multidrug Efflux Systems in Acinetobacter baumannii Using an Efflux-Deficient Bacterial Strain and a Single-Copy Gene Expression System

Published on: January 5, 2024

Sequence and organization of pMAC, an Acinetobacter baumannii plasmid harboring genes involved in organic peroxide

Caleb W Dorsey1, Andrew P Tomaras, Luis A Actis

  • 1Department of Microbiology, Miami University, Oxford, OH, USA.

Plasmid
|March 15, 2006
PubMed

Insights

This study identifies novel genes on the pMAC plasmid in Acinetobacter baumannii responsible for organic peroxide resistance. These findings suggest extrachromosomal elements can facilitate the spread of oxidative stress protection mechanisms in bacteria.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Acinetobacter baumannii is an opportunistic pathogen.
  • Extrachromosomal elements like plasmids play significant roles in bacterial adaptation and virulence.
  • Oxidative stress is a major challenge for bacterial survival.

Purpose of the Study:

  • To characterize the genetic determinants of organic peroxide resistance in Acinetobacter baumannii 19606.
  • To investigate the role of the pMAC plasmid in conferring resistance to organic hydroperoxides.
  • To identify specific genes responsible for detoxification and resistance mechanisms.

Main Methods:

  • Plasmid DNA analysis and mapping using cloning and transformation experiments.
  • Subcloning and tri-parental mating to identify functional regions.
  • Disk diffusion assays to assess resistance to organic peroxides.
  • Gene expression analysis by cloning ORFs into Escherichia coli.

Main Results:

  • Replication and mobilization functions of the pMAC plasmid were mapped to specific regions and open-reading frames (ORFs).
  • ORF 8, encoding a protein similar to hydroperoxide reductase (Ohr), and an adjacent MarR family regulator were identified.
  • Acinetobacter baumannii 19606 exhibited resistance to cumene hydroperoxide (CHP) and tert-butyl hydroperoxide (t-BHP).
  • Introduction of ohr and marR ORFs into E. coli enhanced resistance to CHP and t-BHP.

Conclusions:

  • The pMAC plasmid carries genetic determinants, including ohr and marR, that confer resistance to organic peroxides.
  • This is the first report of organic peroxide resistance genes located on an extrachromosomal element in bacteria.
  • The plasmid-borne nature of these genes facilitates horizontal gene transfer, potentially spreading oxidative stress resistance.

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