Role of AmpD, OprF and penicillin-binding proteins in β-lactam resistance in clinical isolates of Pseudomonas aeruginosa

Abstract

In this study, the mechanisms leading to increased chromosomal AmpCβ-lactamase expression and the contributory roles of the outer-membrane protein OprF and penicillin-binding proteins were analysed in 33 characterized clinical isolates ofPseudomonas aeruginosa. The genesampDandampEwere analysed by PCR and DNA sequencing. Expression of the geneoprFwas assessed using real-time RT-PCR, and penicillin-binding proteins were analysed using a chemiluminescence assay. Several of the isolates with increasedampCexpression had major deletions affectingampD, although in some isolates the mechanism of increasedampCexpression could not be ascertained. Occasional isolates had increased expression of bothampCandoprFbut remained susceptible to cephalosporins, suggesting that increasedβ-lactamase activity could not offset increased outer-membrane permeability. There were no discernible changes in penicillin-binding proteins. Genomic deletions inampDwere observed in selected clinical isolates ofP. aeruginosawith increased expression of the AmpCβ-lactamase. For some isolates, cephalosporin resistance was dependent upon the interplay ofampCandoprFexpression.