Characterization of poxB, a Chromosomal-Encoded Pseudomonas Aeruginosa Oxacillinase

Gene. 2005 Sep 26;358:82-92. doi: 10.1016/j.gene.2005.05.027.


Pseudomonas aeruginosa is the major pathogen associated with morbidity and mortality of patients with cystic fibrosis. One of the reasons for the failure of beta-lactam antibiotic regimens appears to be mediated by de-regulation of the ampC gene, encoding the chromosomal Ambler's Class C beta-lactamase. Currently, the AmpC is the only known chromosomal beta-lactamase whose expression is regulated by a transcriptional regulator, AmpR. We generated an ampC mutation in the prototypic P. aeruginosa strain PAO1. The mutation in ampC did not abolish the beta-lactamase activity entirely suggesting the expression of yet another unreported beta-lactamase. Our genomic analysis revealed the presence of an open reading frame encoding a protein with high homology to the Class D beta-lactamases, commonly known as oxacillinases. The gene was named poxB for Pseudomonas oxacillinase. Cloning and expression of poxB in Escherichia coli conferred beta-lactam resistance to the host. We detected the presence of poxB both in clinical and environmental isolates. Our studies show that P. aeruginosa possesses two beta-lactamases, AmpC and PoxB, which contribute to its resistance against a wide spectrum of beta-lactam antibiotics.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Chromosomes, Bacterial / genetics*
  • Cystic Fibrosis / microbiology
  • Cystic Fibrosis / mortality
  • Drug Resistance, Bacterial / genetics*
  • Escherichia coli / genetics
  • Gene Expression Regulation, Bacterial / physiology*
  • Humans
  • Molecular Sequence Data
  • Phylogeny
  • Pseudomonas Infections / enzymology
  • Pseudomonas Infections / genetics
  • Pseudomonas Infections / mortality
  • Pseudomonas aeruginosa / enzymology
  • Pseudomonas aeruginosa / genetics*
  • beta-Lactamases / genetics*
  • beta-Lactamases / metabolism


  • Bacterial Proteins
  • AmpR protein, Bacteria
  • AmpC beta-lactamases
  • beta-Lactamases
  • oxacillinase