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 ofPseudomonas aeruginosa. We found that there are 51 nucleotide variations at 34 loci over theampGgenes from 24 of 35P. aeruginosastrains detected, of which 7 nucleotide variations resulted in amino acid change. TheampGvariants with the changed nucleotides (amino acids) could complement the function ofampGdeleted PA01 (PA01ΔG). The ampicillin minimum inhibitory concentration (MIC) of PA01ΔG complemented with 32ampGvariants 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 AmpCβ-lactamase decreased as well. By contrast, the ampicillin MIC and the activity of AmpCβ-lactamase remained unchanged for W90R and W90S mutants. Our studies demonstrated that although nucleotide variations occurred in most of theampGgenes, the structure of AmpG protein in clinical isolates is stable, and conservative amino acid is necessary to maintain normal function of AmpG.