title: Pharmacodynamic evaluation of the intracellular activity of antibiotics towards Pseudomonas aeruginosa PAO1 in a model of THP-1 human monocytes.
abstract: Pseudomonas aeruginosa invades epithelial and phagocytic cells, which may play an important role in the persistence of infection. We have developed a 24-h model of THP-1 monocyte infection with P. aeruginosa PAO1 in which bacteria are seen multiplying in vacuoles by electron microscopy. The model has been used to quantitatively assess antibiotic activity against intracellular and extracellular bacteria by using a pharmacodynamic approach (concentration-dependent experiments over a wide range of extracellular concentrations to calculate bacteriostatic concentrations [Cs] and maximal relative efficacies [Emax]; Hill-Langmuir equation). Using 16 antipseudomonal antibiotics (three aminoglycosides, nine β-lactams, three fluoroquinolones, and colistin), dose-response curves were found to be undistinguishable for antibiotics of the same pharmacological class if data were expressed as a function of the corresponding MICs. Extracellularly, all of the antibiotics reached a bacteriostatic effect at their MIC, and their Emax exceeded the limit of detection (-4.5 log(10) CFU compared to the initial inoculum). Intracellularly, Cs values remained unchanged for β-lactams, fluoroquinolones, and colistin but were approximately 10 times higher for aminoglycosides, whereas Emax values were markedly reduced (less negative), reaching -3 log(10) CFU for fluoroquinolones and only -1 to -1.5 log(10) CFU for all other antibiotics. The decrease in intracellular aminoglycoside potency (higher Cs) can be ascribed to the acid pH to which bacteria are exposed in vacuoles. The decrease in the Emax may reflect a reversible alteration of bacterial responsiveness to antibiotics in the intracellular milieu. The model may prove useful for comparison of antipseudomonal antibiotics to reduce the risk of persistence or relapse of pseudomonal infections.
authors.affiliation: Pharmacologie Cellulaire et Moléculaire, Louvain Drug Research Institute, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: Julien M
authors.initials: JM
authors.lastname: Buyck
authors.forename: Paul M
authors.initials: PM
authors.lastname: Tulkens
authors.forename: Françoise
authors.initials: F
authors.lastname: Van Bambeke
mesh_terms: D000617:Aminoglycosides / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001692:Biological Transport; D002460:Cell Line; D002463:Cell Membrane Permeability; D003091:Colistin / Q000494:pharmacology*; D015169:Colony Count, Microbial; D004305:Dose-Response Relationship, Drug; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008826:Microbial Sensitivity Tests; D015233:Models, Statistical; D009000:Monocytes / Q000187:drug effects / Q000382:microbiology; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D014617:Vacuoles / Q000187:drug effects / Q000382:microbiology; D047090:beta-Lactams / Q000494:pharmacology*
chemical_list: D000617:Aminoglycosides; D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D047090:beta-Lactams; D003091:Colistin