Objectives: To characterize the mechanisms involved in the reduced carbapenem susceptibility of five Acinetobacter pittii strains isolated from different regions of Germany.
Methods: The strains were analysed by susceptibility testing, phenotypic tests for metallo-β-lactamase production, sequencing of the integron structure and strain typing by PFGE, as well as multilocus sequence typing (MLST) and plasmid analysis by S1 restriction and hybridization.
Results: Despite GIM-1 production, the MICs of imipenem were only 4 mg/L for four strains and some methods of phenotypic MBL detection failed. According to PFGE and MLST, the strains belonged to four different clones, but blaGIM-1 was present in identical integron structures in all strains and carried on plasmids of ∼60 kb.
Conclusions: For the first time, GIM-1 has been demonstrated in A. pittii. This resistance mechanism has previously been reported only in Enterobacteriaceae and Pseudomonas aeruginosa. As GIM-1 was found in strains with diverse clonal backgrounds, but encoded on plasmids of a similar size, further spread among Acinetobacter spp. seems possible. The detection of GIM-1 production might be challenging in some strains due to the low MICs of carbapenems.
Keywords: PFGE; carbapenemases; integrons; multilocus sequence typing; plasmids.