title: Development and persistence of antimicrobial resistance in Pseudomonas aeruginosa: a longitudinal observation in mechanically ventilated patients.
abstract: Intubated patients frequently become colonized by Pseudomonas aeruginosa, which is subsequently responsible for ventilator-associated pneumonia. This pathogen readily acquires resistance against available antimicrobials. Depending on the resistance mechanism selected for, resistance might either be lost or persist after removal of the selective pressure. We investigated the rapidity of selection, as well as the persistence, of antimicrobial resistance and determined the underlying mechanisms. We selected 109 prospectively collected P. aeruginosa tracheal isolates from two patients based on their prolonged intubation and colonization periods, during which they had received carbapenem, fluoroquinolone (FQ), or combined beta-lactam-aminoglycoside therapies. We determined antimicrobial resistance phenotypes by susceptibility testing and used quantitative real-time PCR to measure the expression of resistance determinants. Within 10 days after the initiation of therapy, all treatment regimens selected resistant isolates. Resistance to beta-lactam and FQ was correlated with ampC and mexC gene expression levels, respectively, whereas imipenem resistance was attributable to decreased oprD expression. Combined beta-lactam-aminoglycoside resistance was associated with the appearance of small-colony variants. Imipenem and FQ resistance persisted for prolonged times once the selecting antimicrobial treatment had been discontinued. In contrast, resistance to beta-lactams disappeared rapidly after removal of the selective pressure, to reappear promptly upon renewed exposure. Our results suggest that resistant P. aeruginosa is selected in less than 10 days independently of the antimicrobial class. Different resistance mechanisms lead to the loss or persistence of resistance after the removal of the selecting agent. Even if resistant isolates are not evident upon culture, they may persist in the lung and can be rapidly reselected.
authors.affiliation: Département de Microbiologie et de Médecine Moléculaire, Centre Médical Universitaire de Genève, and Laboratoire Central de Bactériologie, Service des Soins Intensifs, Hôpital Universitaire de Genève, Geneva, Switzerland.
authors.forename: Anita
authors.initials: A
authors.lastname: Reinhardt
authors.forename: Thilo
authors.initials: T
authors.lastname: Köhler
authors.forename: Paul
authors.initials: P
authors.lastname: Wood
authors.forename: Peter
authors.initials: P
authors.lastname: Rohner
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Dumas
authors.forename: Bara
authors.initials: B
authors.lastname: Ricou
authors.forename: Christian
authors.initials: C
authors.lastname: van Delden
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D006801:Humans; D008137:Longitudinal Studies; D053717:Pneumonia, Ventilator-Associated / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D011552:Pseudomonas Infections / Q000188:drug therapy; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001618:beta-Lactamases