Efficacy and Potential for Resistance Selection of Antipseudomonal Treatments in a Mouse Model of Lung Infection by HypermutablePseudomonas aeruginosa

Abstract

Hypermutable Pseudomonas aeruginosa strains are found with high frequency in the lungs of patients with chronic infections and are associated with high antibiotic resistance rates. The in vivo consequences of hypermutation for treatment in a mouse model of lung infection using strain PAO1 and its hypermutable derivative PAO⌬mutS are investigated. Groups of 30 mice were treated for 3 days with humanized regimens of ciprofloxacin (CIP), tobramycin (TOB), CIP plus TOB, or placebo, and mortality, total lung bacterial load, and 4؋-and 16؋-MIC mutants were recorded. The rates of mutation and the initial in vivo frequencies of mutants (at the onset of treatment) were also estimated and the in vitro-and in vivo-selected mutants characterized. Since both strains had identical MICs, the same pharmacokinetic/pharmacodynamic (PK/PD) parameters were obtained: area under the 24-h concentration-time curve (fAUC)/MIC ‫؍‬ 385 for CIP and maximum concentration of drug in serum (fC max )/MIC ‫؍‬ 19 for TOB. Despite adequate PK/PD parameters, persistence of high bacterial numbers and amplification (50,000-fold) of resistant mutants (MexCD-OprJ hyperexpression) were documented with CIP treatment for PAO⌬mutS, in contrast to complete resistance suppression for PAO1 (P < 0.01), showing that conventional PK/PD parameters may not be applicable to infections by hypermutable strains. On the other hand, the efficacy of TOB monotherapy in terms of mortality reduction and bacterial load was very low regardless of the strain but not due to resistance development, since mutants were not selected for PAO1 and were only modestly amplified for PAO⌬mutS. Finally, the CIP-plus-TOB combination was synergistic, further reducing mortality and bacterial load and completely preventing resistance even for PAO⌬mutS (P < 0.01 compared to monotherapy), showing that it is possible to suppress resistance selection in infections by hypermutable P. aeruginosa using appropriate combined regimens.

Nosocomial Outbreak of a Non-Cefepime-Susceptible Ceftazidime-Susceptible Pseudomonas aeruginosa Strain Overexpressing MexXY-OprM and Producing an Integron-Borne PSE-1 ß-Lactamase

“…The breakpoint used for MexAB-OprM hyperproduction was a threefold higher level of expression than that by PAO1. Previously obtained or constructed PAO1 mutants that hyperproduce AmpC or the several efflux pumps were used as controls in the RT-PCR experiments (18,21,23 …”

Inactivation of the Mismatch Repair System in Pseudomonas aeruginosa Attenuates Virulence but Favors Persistence of Oropharyngeal Colonization in Cystic Fibrosis Mice

“…The presence of hypermutable strains has been found to be linked to the high antibioticresistance rates of P. aeruginosa clinical isolates recovered from patients with chronic lung infections (1,9,11,16), and in vitro and in vivo experiments have shown that hypermutation dramatically speeds up resistance development during exposure to antimicrobial agents (1,12). Nevertheless, except for antimicrobial resistance development, a link between hypermutation and the genetic adaptation required for the longterm persistence of chronic infections has not yet been proved.…”

Association between Hypermutator Phenotype, Clinical Variables, Mucoid Phenotype, and Antimicrobial Resistance in Pseudomonas aeruginosa

“…Alhough this is the first time this association has been demonstrated, it is not surprising because both of these phenotypes increase with duration of infection in the CF lung (3,10). The mucoid phenotype is thought to protect bacteria against certain antimicrobials (1, 7), innate immune factors (9), and reactive oxygen species (8), and hypermutators increase the fitness of a bacterial population undergoing stress and increase the likelihood of antimicrobial resistance (11,13,15,17). There may also be an interaction between the two phenotypes; hypermutators undergo mutations at a higher rate and are therefore more likely to acquire a mutation resulting in the mucoid phenotype.…”

“…Patients with CF commonly harbor hypermutator isolates of this bacterium (3,16), the prevalence of which increases with duration of infection (3), but no other clinical correlates of hypermutator presence have been determined. Hypermutators are more resistant to antimicrobials in vitro (3,11) and in vivo (13) and may increase the fitness of bacterial populations during environmental stress (17).…”