In Vivo Selection of Reduced Susceptibility to Carbapenems in Acinetobacter baumannii Related to IS Aba1 -Mediated Overexpression of the Natural bla OXA-66 Oxacillinase Gene

Abstract
Two clonally related Acinetobacter baumannii isolates, A1 and A2, were obtained from the same patient. Isolate A2, selected after an imipenem-containing treatment, showed reduced susceptibility to carbapenems. This resistance pattern was related to insertion of the IS Aba1 element upstream of the naturally occurring bla OXA-66 carbapenemase gene as demonstrated by sequencing, reverse transcription-PCR analysis, and inactivation of the bla OXA-66 gene.