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Site-specific Bacterial Chromosome Engineering: ΦC31 Integrase Mediated Cassette Exchange (IMCE)
08:21

Site-specific Bacterial Chromosome Engineering: ΦC31 Integrase Mediated Cassette Exchange (IMCE)

Published on: March 16, 2012

Integron-located oxa-32 gene cassette encoding an extended-spectrum variant of OXA-2 beta-lactamase from Pseudomonas

Laurent Poirel1, Patrick Gerome, Christophe De Champs

  • 1Service de Bactériologie-Virologie, Hôpital de Bicêtre, Assistance Publique/Hôpitaux de Paris, Faculté de Médecine Paris-Sud, 94275 Le Kremlin-Bicêtre, France.

Antimicrobial Agents and Chemotherapy
|January 18, 2002
PubMed

Insights

A Pseudomonas aeruginosa isolate resistant to ceftazidime carried a plasmid with genes for OXA-32 beta-lactamase and AAC(6')Ib(9) aminoglycoside acetyltransferase. The Ile169 substitution in OXA-32 confers ceftazidime resistance.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Antimicrobial Resistance

Background:

  • Pseudomonas aeruginosa is an opportunistic pathogen frequently associated with hospital-acquired infections.
  • The emergence of multidrug-resistant strains, particularly those resistant to third-generation cephalosporins like ceftazidime, poses a significant clinical challenge.

Purpose of the Study:

  • To investigate the genetic basis of ceftazidime resistance in a clinical isolate of Pseudomonas aeruginosa.
  • To characterize the beta-lactamase responsible for ceftazidime resistance and its specific mutations.

Main Methods:

  • Plasmid isolation and characterization from Pseudomonas aeruginosa clinical isolate CY-1.
  • Identification and sequencing of gene cassettes within a class 1 integron.
  • Site-directed mutagenesis to determine the role of specific amino acid substitutions in beta-lactamase activity.

Main Results:

  • A ca. 250-kb conjugative plasmid containing a class 1 integron was identified in the ceftazidime-resistant isolate.
  • The integron harbored gene cassettes encoding OXA-32 (an OXA-2-type beta-lactamase) and AAC(6 oun)Ib(9).
  • Site-directed mutagenesis confirmed that the Leu169Ile substitution in OXA-32 is responsible for ceftazidime resistance, but not cefotaxime resistance.

Conclusions:

  • The OXA-32 beta-lactamase, with a specific amino acid substitution, is a key determinant of ceftazidime resistance in this Pseudomonas aeruginosa isolate.
  • The presence of this resistance mechanism on a conjugative plasmid highlights the potential for rapid dissemination of antimicrobial resistance genes.

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