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Distribution and expression of the Ade multidrug efflux systems in Acinetobacter baumannii clinical isolates

Sirawit Pagdepanichkit1, Chanwit Tribuddharat2, Rungtip Chuanchuen1

  • 1a Research Unit in Microbial Food Safety and Antimicrobial Resistance, Department of Veterinary Public Health, Faculty of Veterinary Science, Chulalongkorn University, Bangkok 10330, Thailand.

Canadian Journal of Microbiology
|June 23, 2016
PubMed

Insights

Multidrug resistance in Acinetobacter baumannii is often linked to efflux pumps. This study found widespread expression of resistant-nodulation-cell division (RND)-type efflux systems, but their regulation is complex.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Antimicrobial Resistance

Background:

  • Acinetobacter baumannii is a significant opportunistic pathogen.
  • Multidrug resistance (MDR) in A. baumannii is a growing global health concern.
  • Resistant-nodulation-cell division (RND)-type efflux pumps are key contributors to MDR in bacteria.

Purpose of the Study:

  • To investigate the expression of four RND-type multidrug efflux systems (AdeABC, AdeDE, AdeIJK, AdeFGH) in clinical isolates of A. baumannii.
  • To determine the association between efflux pump expression and antimicrobial susceptibility.
  • To explore the regulatory mechanisms underlying efflux pump expression.

Main Methods:

  • Antimicrobial susceptibility testing of 100 A. baumannii clinical isolates.
  • Inhibition assays using reserpine and carbonyl cyanide m-chlorophenylhydrazone (CCCP).
  • RT-PCR to assess the expression of RND-type efflux pump genes (AdeABC, AdeDE, AdeIJK, AdeFGH).
  • Determination of transcription levels and screening for regulatory mutations in selected isolates.

Main Results:

  • All isolates exhibited multidrug resistance.
  • Efflux pumps were associated with the MDR phenotype in most isolates.
  • 97% of isolates expressed at least one RND-type efflux pump, with AdeIJK being the most common (97%).
  • AdeDE was not detected in any isolate.
  • 52% of isolates co-expressed up to three RND-type efflux systems.
  • No strong correlation was found between specific efflux pump expression and antimicrobial resistance profiles.
  • Overexpression of certain pumps was not always linked to mutations in their regulatory genes.

Conclusions:

  • RND-type efflux pumps are universally present in the studied A. baumannii isolates, with varying expression levels.
  • The regulation of RND-type efflux pump expression in A. baumannii is complex and not solely dependent on mutations in known regulatory genes.
  • Efflux pump activity significantly contributes to the multidrug resistance phenotype in A. baumannii.
Keywords:
Acinetobacter baumanniiRND-type efflux systemsmultidrug resistancerésistance multimédicamenteusesystèmes d’efflux de type RND

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