TABLE 2

Strains and plasmids used in this study

Strain or plasmid (laboratory reference no.)DescriptionaReference or source
Strains
    A. baumannii
        6009-1A. baumannii clinical strain isolated before colistin treatment from a patient at Egas Moniz Hospital, Portugal; displays intermediate levels of colistin resistance (MIC, 4–16 μg/ml)Miguel Viveiros, Institute of Hygiene and Tropical Medicine, Universidade Nova de Lisboa
        6009-2A. baumannii clinical strain isolated from the same patient as described above following 11 days of colistin treatment; high/very high colistin resistance (MIC, 64–128 μg/ml)Miguel Viveiros, Institute of Hygiene and Tropical Medicine, Universidade Nova de Lisboa
        6009-2/pWH1266::hns (AL2430)Strain 6009-2 containing a functional copy of hns (amplified from 6009-1) cloned into pWH1266; TetrThis study
        6009-2/pWH1266 (AL2434)Strain 6009-2 containing the empty vector pWH1266; Ampr TetrThis study
        6009-1/pWH1266::eptA (AL2702)Strain 6009-1 containing a functional copy of eptA cloned into pWH1266; TetrThis study
        6009-1/pWH1266 (AL2706)Strain 6009-1 containing empty vector pWH1266; Ampr TetrThis study
        6009-1 Δhns (AL2835)6009-1 hns deletion mutant, generated by double-crossover allelic exchange mutagenesis; TetrThis study
    E. coli
        DH5αE. coli, F Φ80lacZΔM15 Δ(lacZYA-argF) U169 recA1 endA1 hsdR17 (rK mK+) phoA supE44 λ thi-1 gyrA96 relA1Bethesda Research Laboratories
Plasmids
    pWH1266A. baumannii/E. coli shuttle vector, 8.9 kb, Ampr Tetr61
    pWH1266::hnspWH1266 containing the wild-type hns gene PCR amplified from A. baumannii strain 6009-1This study
    pWH1266::eptApWH1266 containing the eptA gene PCR amplified from A. baumannii strain 6009-2This study
  • a Tetr, tetracycline resistant; Ampr, ampicillin resistant.