Results of susceptibility testing (MICs), the molecular analyses of β-lactamases and porins, the efflux properties (EHT), and the synergism testing (FICIs).

The EHT and the FICI values are given as median ± standard deviation. Synergistic FICI values are indicated in bold letters. The FICI values indicated in brackets represent the lowest values for the given combination.

*Strains were obtained from: NRZ = National Reference Laboratory for multidrug-resistant gram-negative bacteria, Ruhr-University Bochum, Germany, and RKI = Robert-Koch-Institut, Wernigerode, Germany; MEM = meropenem; CST = colistin; TCG = tigecycline; FICI = fractional inhibitory concentration index; EHT = efflux half-time; nm = not measureable; aa = amino acid;:: = gene dispuption by insertion sequence; del = deletion; ins insertion; sub = substitution;

**non-functional (STOP mutation in blaOXA-9 gene)

Results of susceptibility testing (MICs), the molecular analyses of β-lactamases and porins, the efflux properties (EHT), and the synergism testing (FICIs).