In vitro selection of resistance in Pseudomonas aeruginosa and Acinetobacter spp. by levofloxacin and ciprofloxacin alone and in combination with beta-lactams and amikacin
Articolo
Data di Pubblicazione:
2005
Citazione:
In vitro selection of resistance in Pseudomonas aeruginosa and Acinetobacter spp. by levofloxacin and ciprofloxacin alone and in combination with beta-lactams and amikacin / L. Drago, E. De Vecchi, L. Nicola , L. Tocalli, M.R. Gismondo. - In: JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY. - ISSN 0305-7453. - 56:2(2005), pp. 353-359.
Abstract:
Objectives: The aim of this study was to evaluate the ability of levofloxacin and ciprofloxacin alone and in combination with either ceftazidime, cefepime, imipenem, piperacillin–tazobactam or amikacin to select for antibiotic-resistant mutants of Pseudomonas aeruginosa and Acinetobacter spp.
Methods: Clinical strains of P. aeruginosa (n = 5) and Acinetobacter spp. (n = 5) susceptible to all the drugs used in the study were assayed. Development of resistance was determined by multi-step and single-step methodologies. For multi-step studies, MICs were determined after five serial passages on antibiotic-gradient plates containing each antibiotic alone or in combination with levofloxacin or ciprofloxacin. Acquisition of resistance was defined as an increase of ≥4-fold from the starting MIC. In single-step studies, the frequency of spontaneous mutations was calculated after a passage on plates containing antibiotics alone and in combinations at concentrations equal to the highest NCCLS breakpoints.
Results: Serial passages on medium containing single antibiotics resulted in increased MICs for each antibiotic; MIC increases were limited by antibiotics in combination. A decrease in the number of strains with MICs above the NCCLS breakpoints occurred when fluoroquinolones were combined with a second antibiotic for both P. aeruginosa and Acinetobacter spp. isolates. Frequencies of mutation were higher for antibiotics alone than for combinations.
Conclusions: Use of combinations of fluoroquinolones with β-lactams and amikacin reduces the risk for in vitro selection of resistant P. aeruginosa and Acinetobacter spp.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
levofloxacin ; antibacterial activity ; mutation frequencies ; β-lactams ; fluoroquinolones
Elenco autori:
L. Drago, E. De Vecchi, L. Nicola , L. Tocalli, M.R. Gismondo
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