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Increased expression of ampC in Pseudomonas aeruginosa mutants selected with ciprofloxacin

Daniel J Wolter1, Amber J Schmidtke, Nancy D Hanson

  • 1Center for Research in Anti-Infectives and Biotechnology, Department of Medical Microbiology and Immunology, Creighton University School of Medicine, Omaha, NE 68178, USA.

Antimicrobial Agents and Chemotherapy
|May 23, 2007
PubMed

Insights

Ciprofloxacin exposure induced increased ampC expression in Pseudomonas aeruginosa mutants. AmpD complementation normalized ampC expression, suggesting novel regulatory pathways beyond known mutations.

Area of Science:

  • Microbiology
  • Bacterial genetics
  • Antibiotic resistance

Background:

  • Pseudomonas aeruginosa is an opportunistic pathogen known for its intrinsic and acquired resistance to antibiotics.
  • The beta-lactamase AmpC is a key enzyme conferring resistance to beta-lactam antibiotics, including cephalosporins.
  • Multidrug efflux pumps, such as MexCD-OprJ, contribute to antibiotic resistance in P. aeruginosa.

Purpose of the Study:

  • To investigate the mechanisms underlying increased ampC expression in Pseudomonas aeruginosa mutants selected during ciprofloxacin exposure.
  • To determine the relationship between ampC and mexCD-oprJ expression.
  • To identify potential regulatory elements or mutations responsible for altered ampC expression.

Main Methods:

  • Exposure of Pseudomonas aeruginosa to ciprofloxacin to select for resistant mutants.
  • Quantitative analysis of ampC and mexCD-oprJ gene expression.
  • Genetic analysis including mutation screening in ampR, intergenic regions, and ampD family genes.
  • Functional complementation studies using an ampD-expressing plasmid.

Main Results:

  • Two P. aeruginosa mutants displayed significantly increased ampC and mexCD-oprJ expression upon ciprofloxacin exposure.
  • No direct correlation was found between elevated mexCD-oprJ and ampC expression.
  • Increased ampC expression was not attributed to mutations in ampR, the ampC-ampR intergenic region, ampD, ampDh2, or ampDh3.
  • Complementation with a functional ampD gene restored wild-type ampC expression levels and ceftazidime susceptibility.

Conclusions:

  • Ciprofloxacin selection can lead to increased ampC expression in P. aeruginosa through mechanisms independent of known mutations in ampR or ampD.
  • The MexCD-OprJ efflux system is upregulated concurrently but not causally linked to ampC induction in these mutants.
  • Functional AmpD protein plays a critical role in regulating ampC expression, highlighting alternative regulatory pathways.

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