Pseudo-outbreak of imipenem-resistant Acinetobacter baumannii resulting from false susceptibility testing by a rapid automated system

Introduction of the Vitek GNS-506 susceptibility testing cards in the Hippo kration General Hospital, Thessaloniki, Greece, resulted in an apparently h igh prevalence of imipenem-resistant Acinetobacter baumannii. When 35 of th ese isolates were further tested by disk diffusion, broth microdilution, an d agar dilution assays, 32 were imipenem sensitive by ail tests and three w ere sensitive or intermediate, depending on the method. The pseudoresistant acinetobacters did not form a genetically homogeneous group. It is suggest ed that the detection of imipenem-resistant A. baumannii isolates by this s ystem should be confirmed by an additional susceptibility test.