ABSTRACT Multiresistant Acinetobacter baumannii , a common etiologic agent of severe nosocomial infections in compromised hosts, usually harbors aac(6 ′ )-Ib. This gene specifies resistance to amikacin and other aminoglycosides, seriously limiting the effectiveness of these antibiotics. An antisense oligodeoxynucleotide (ODN4) that binds to a duplicated sequence on the aac(6 ′ )-Ib mRNA, one of the copies overlapping the initiation codon, efficiently inhibited translation in vitro . An isosequential nuclease-resistant hybrid oligomer composed of 2′,4′-bridged nucleic acid-NC (BNA ^NC ) residues and deoxynucleotides (BNA ^NC -DNA) conjugated to the permeabilizing peptide (RXR) ₄ XB (“X” and “B” stand for 6-aminohexanoic acid and β-alanine, respectively) (CPPBD4) inhibited translation in vitro at the same levels observed in testing ODN4. Furthermore, CPPBD4 in combination with amikacin inhibited growth of a clinical A. baumannii strain harboring aac(6 ′ )-Ib in liquid cultures, and when both compounds were used as combination therapy to treat infected Galleria mellonella organisms, survival was comparable to that seen with uninfected controls.