title: Benefit of having multiple ampD genes for acquiring beta-lactam resistance without losing fitness and virulence in Pseudomonas aeruginosa.
abstract: The inactivation of ampD in Pseudomonas aeruginosa leads to a partially derepressed phenotype, characterized by a moderately high level basal ampC expression that is still further inducible, due to the presence of two additional ampD genes in this species (ampDh2 and ampDh3). The sequential inactivation of the three ampD genes was shown to lead to a stepwise upregulation of ampC expression, reaching full derepression in the triple mutant. To gain insight into the biological role of P. aeruginosa AmpD multiplicity, we determined the effects of the inactivation of the ampD genes on fitness and virulence. We show that, in contrast to what was previously documented for Salmonella spp., the inactivation of ampD in P. aeruginosa does not affect fitness or virulence in a mouse model of systemic infection. This lack of effect was demonstrated to be dependent on the presence of the additional ampD genes (ampDh2 and ampDh3), since the double and the triple ampD mutants completely lost their biological competitiveness and virulence; full ampC derepression and disruption of the AmpD peptidoglycan recycling system itself are both found to cause a major biological cost. Furthermore, among the ampD genes, ampDh3 is found to be the most relevant for virulence in P. aeruginosa. Therefore, as a consequence of the presence of additional ampD genes, partial ampC derepression mediated by ampD inactivation confers a biologically efficient resistance mechanism on P. aeruginosa.
authors.affiliation: Servicio de Microbiología, Hospital Son Dureta, Palma de Mallorca, Spain.
authors.forename: Bartolomé
authors.initials: B
authors.lastname: Moya
authors.forename: Carlos
authors.initials: C
authors.lastname: Juan
authors.forename: Sebastián
authors.initials: S
authors.lastname: Albertí
authors.forename: José L
authors.initials: JL
authors.lastname: Pérez
authors.forename: Antonio
authors.initials: A
authors.lastname: Oliver
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002442:Ceftazidime / Q000494:pharmacology; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004195:Disease Models, Animal; D017353:Gene Deletion; D018628:Gene Dosage; D015870:Gene Expression; D005798:Genes, Bacterial; D006801:Humans; D066298:In Vitro Techniques; D051379:Mice; D008813:Mice, Inbred ICR; D009154:Mutation; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics*; D010641:Phenotype; D011552:Pseudomonas Infections / Q000188:drug therapy / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology; D014774:Virulence / Q000235:genetics; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D002442:Ceftazidime; C062460:AmpD protein, Bacteria; D009238:N-Acetylmuramoyl-L-alanine Amidase; C048795:AmpC beta-lactamases; D001618:beta-Lactamases