Pulmonary infections caused by Acinetobacter baumannii are often difficult to treat due to multidrug resistance and require last resort molecules such as polymyxins. Revaluation of these antibiotics is necessary to optimize their use. However, optimizing antibiotic dosing regimens based on in vitro data produced under non-physiological conditions constitute a potential contributor to resistance development. The aim of this project is to investigate alternative in vivo relevant testing conditions for their impact on antibiotic activity and bacteria susceptibility/resistance. Obtained data will be connected with modelling for a parallel improvement of semi-mechanistic PK/PD models as well as in vitro testing conditions.