title: Development of Antibiotic Resistance during Simulated Treatment of Pseudomonas aeruginosa in Chemostats.
abstract: During treatment of infections with antibiotics in critically ill patients in the intensive care resistance often develops. This study aims to establish whether under those conditions this resistance can develop de novo or that genetic exchange between bacteria is by necessity involved. Chemostat cultures of Pseudomonas aeruginosa were exposed to treatment regimes with ceftazidime and meropenem that simulated conditions expected in patient plasma. Development of antibiotic resistance was monitored and mutations in resistance genes were searched for by sequencing PCR products. Even at the highest concentrations that can be expected in patients, sufficient bacteria survived in clumps of filamentous cells to recover and grow out after 3 to 5 days. At the end of a 7 days simulated treatment, the minimal inhibitory concentration (MIC) had increased by a factor between 10 and 10,000 depending on the antibiotic and the treatment protocol. The fitness costs of resistance were minimal. In the resistant strains, only three mutations were observed in genes associated with beta-lactam resistance. The development of resistance often observed during patient treatment can be explained by de novo acquisition of resistance and genetic exchange of resistance genes is not by necessity involved. As far as conclusions based on an in vitro study using P. aeruginosa and only two antibiotics can be generalized, it seems that development of resistance can be minimized by treating with antibiotics in the highest concentration the patient can endure for the shortest time needed to eliminate the infection.
authors.affiliation: Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute of Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Feng
authors.affiliation: Department of Medical Microbiology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Caspar J
authors.initials: CJ
authors.lastname: Hodiamont
authors.affiliation: Department of Hospital Pharmacy & Clinical Pharmacology, Academic Medical Center, Amsterdam, the Netherlands.
authors.forename: Reinier M
authors.initials: RM
authors.lastname: van Hest
authors.affiliation: Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute of Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Stanley
authors.initials: S
authors.lastname: Brul
authors.affiliation: Department of Medical Microbiology, Academic Medical Center, Amsterdam, the Netherlands.|Department of Global Health-Amsterdam Institute for Global Health and Development, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Constance
authors.initials: C
authors.lastname: Schultsz
authors.affiliation: Department of Molecular Biology and Microbial Food Safety, Swammerdam Institute of Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.|Office for Risk Assessment and Research Coordination Netherlands Food and Consumer Product Safety Authority, Utrecht, The Netherlands.
authors.forename: Benno H
authors.initials: BH
authors.lastname: Ter Kuile
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002442:Ceftazidime / Q000494:pharmacology*; D004352:Drug Resistance, Microbial; D006801:Humans; D000077731:Meropenem; D008826:Microbial Sensitivity Tests; D009154:Mutation / Q000187:drug effects; D011552:Pseudomonas Infections / Q000188:drug therapy* / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development; D013845:Thienamycins / Q000494:pharmacology*; D018440:beta-Lactam Resistance
chemical_list: D000900:Anti-Bacterial Agents; D013845:Thienamycins; D002442:Ceftazidime; D000077731:Meropenem