ISAba825, a Functional Insertion Sequence Modulating Genomic Plasticity and bla OXA-58 Expression in Acinetobacter baumannii

ISAba825, an insertion sequence found inactivating Acinetobacter baumannii carO, was tagged with a kanamycin (Kn) resistance cassette. ISAba825::Kn effectively transposed in A. baumannii, showing preference for short, AT-enriched target sequences, generating 6- to 9-bp target duplications. Additionally, we detected the presence of ISAba825 upstream of a plasmid-borne bla(OXA-58) gene, generating a hybrid promoter largely enhancing its expression and leading to carbapenem resistance. Overall, a role for ISAba825 in carbapenem resistance modulation in A. baumannii is proposed.