Ann Clin Microbiol 2022;25:125-136. Assessment of the synergistic effect of seven antimicrobial combinations on extensively drug-resistant Acinetobacter baumannii strains
Table 1. Results of time-kill assay against two-drug combinations of colistin and various antibiotics or a peptide for seven extensively drugresistant A. baumannii clinical isolates
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity*
Colistin Doripenem Colistin + Doripenem Colistin + Doripenem Colistin + Doripenem
111-27 9.2 9.2 9.9 0.7 I† NB
111-28 9.3 9.2 9.4 0.2 I NB
111-29 8.6 9.5 9.5 0.9 I NB
111-31 10.1 9.8 9.2 -0.6 I NB
64-26 9.1 9.3 3.4 -5.8 Synergy‡ NB
131-16 6.1 9.2 5.4 -0.7 I NB
130-87 8.0 9.4 8.0 0.0 I NB
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity
Colistin Tigecycline Colistin + Tigecycline Colistin + Tigecycline Colistin + Tigecycline
111-27 9.2 9.1 9.3 0.2 I NB
111-28 9.3 9.4 8.5 -0.8 I NB
111-29 8.6 9.9 9.0 0.4 I NB
111-31 10.1 8.1 5.1 -3.0 Synergy NB
64-26 9.1 9.4 6.4 -2.7 Synergy NB
131-16 6.1 9.2 6.4 0.3 I NB
130-87 8.0 8.5 4.5 -3.5 Synergy NB
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity
Colistin Linezolid Colistin + Linezolid Colistin + Linezolid Colistin + Linezolid
111-27 9.2 8.1 9.3 1.2 I NB
111-28 9.3 9.5 9.4 0.1 I NB
111-29 8.6 9.4 9.0 0.4 I NB
111-31 10.1 9.4 9.4 0.0 I NB
64-26 9.1 9.2 9.3 0.2 I NB
131-16 6.1 9.4 7.4 1.3 I NB
130-87 8.0 10.0 8.3 0.3 I NB
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity
Colistin Fusidic acid Colistin + Fusidic acid Colistin + Fusidic acid Colistin + Fusidic acid
111-27 9.2 9.3 3.8 -5.4 Synergy NB
111-28 9.3 9.3 9.2 -0.1 I NB
111-29 8.6 10.2 9.4 0.8 I NB
111-31 10.1 9.9 9.4 -0.5 I NB
64-26 9.1 9.3 9.4 0.3 I NB
131-16 6.1 9.3 6.4 0.3 I NB
130-87 8.0 9.5 8.3 0.3 I NB
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity
Colistin Minocycline Colistin + Minocycline Colistin + Minocycline Colistin + Minocycline
111-27 9.2 3.3 1.8 -1.5 I B
111-28 9.3 8.5 -1.0 -3.2 Synergy NB
111-29 8.6 9.4 5.4 -3.2 Synergy NB
111-31 10.1 9.4 5.8 -3.6 Synergy NB
64-26 9.1 4.2 3.4 -0.9 I NB
131-16 6.1 5.3 4.2 -1.2 I NB
130-87 8.0 5.5 3.2 -2.3 Synergy NB
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity
Colistin Vancomycin Colistin + Vancomycin Colistin + Vancomycin Colistin + Vancomycin
111-27 9.2 9.2 1.5 -7.7 Synergy B
111-28 9.3 9.2 9.4 0.1 I NB
111-29 8.6 8.2 9.1 0.9 I NB
111-31 10.1 9.5 8.6 -0.9 I NB
64-26 9.1 9.0 6.1 -2.9 Synergy NB
131-16 6.1 9.2 6.4 0.3 I NB
130-87 8.0 9.2 6.6 -1.4 I NB
Strain Log10 (VC) at 24 hr Log10 (VC combination – VCMASA) at 24 hr Interaction Bactericidal activity
Colistin Alyteserin E4K Colistin + Alyteserin E4K Colistin + Alyteserin E4K Colistin + Alyteserin E4K
111-27 9.1 9.1 4.2 -4.9 Synergy NB
111-28 9.3 9.3 9.2 -0.1 I NB
111-29 9.4 9.4 9.3 -0.1 I NB
111-31 9.3 9.3 0.0 -9.3 Synergy B
64-26 9.4 9.4 9.3 -0.1 I NB
131-16 9.2 9.2 0.0 -9.2 Synergy B
130-87 ND ND ND ND ND ND

*≥3 log10 CFU/mL reduction compared with the initial inoculums; † <2 log10 change in CFU/mL at 24 hr with the combination compared with the most active single agent; ‡≥2 log10 CFU/mL reduction with the combination compared with the most active single agent of 24hr. Abbreviation: VC, viable colony count; I, Indifference; NB, non-bactericidal; B, bactericidal; ND, not done; MASA, most active single agent.