The Structure ofampGGene inPseudomonas aeruginosaand Its Effect on Drug Resistance

Abstract

In order to study the relationship between the structure and function of AmpG, structure, site-specific mutation, and gene complementary experiments have been performed against the clinical isolates of Pseudomonas aeruginosa. We found that there are 51 nucleotide variations at 34 loci over the ampG genes from 24 of 35 P. aeruginosa strains detected, of which 7 nucleotide variations resulted in amino acid change. The ampG variants with the changed nucleotides (amino acids) could complement the function of ampG deleted PA01 (PA01ΔG). The ampicillin minimum inhibitory concentration (MIC) of PA01ΔG complemented with 32 ampG variants was up to 512 μg/ml, similar to the original PA01 (P. aeruginosa PA01). Furthermore, site-directed mutation of two conservative amino acids (I53 and W90) showed that when I53 was mutated to 53S or 53T (I53S or I53T), the ampicillin MIC level dropped drastically, and the activity of AmpC β-lactamase decreased as well. By contrast, the ampicillin MIC and the activity of AmpC β-lactamase remained unchanged for W90R and W90S mutants. Our studies demonstrated that although nucleotide variations occurred in most of the ampG genes, the structure of AmpG protein in clinical isolates is stable, and conservative amino acid is necessary to maintain normal function of AmpG.

Class C β-Lactamases: Molecular Characteristics

“…freundii, E. cloacae, and P. aeruginosa (243,244). AmpR loss leads to susceptibility to βlactams, whereas constitutively high levels of ampC expression were reported for clinical isolates and in vitro strains with mutations resulting in AmpR amino-acid substitutions: C. AmpG, an intrinsic membrane protein, displays permease activity mediating the transport of muropeptides from the periplasm to the cytoplasm, such transport being essential for the induction of class C β-lactamases (252)(253)(254). Deletion of the gene encoding this protein in P. aeruginosa results in a lower level of bacterial resistance to ampicillin.…”