In Vitro Synergy of Colistin Combinations against Colistin-Resistant Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae Isolates

摘要: Colistin resistance, although uncommon, is increasingly being reported among Gram-negative clinical pathogens, and an understanding of its impact on the activity antimicrobials now evolving. We evaluated potential for synergy colistin plus trimethoprim, trimethoprim-sulfamethoxazole (1/19 ratio), or vancomycin against 12 isolates Acinetobacter baumannii (n = 4), Pseudomonas aeruginosa Klebsiella pneumoniae 4). The strains included six multidrug-resistant isolates, K. ATCC 700603, A. 19606, P. 27853, their colistin-resistant derivatives (KPm1, ABm1, PAm1, respectively). Antimicrobial susceptibilities were assessed by broth microdilution population analysis profiles. combinations was using a checkerboard assay, as well static time-kill experiments at 0.5× 0.25× MIC. MIC ranges vancomycin, (1/19) ≥128, 4 to 2/38 >128/2,432 μg/ml, respectively. resistance demonstrated little values. Isolates with subpopulations heterogeneously resistant observed various degrees in all tested isolates. In assays, synergistic KPm1 ABm1 PAm1 contrast, none any colistin-susceptible Only trimethoprim bactericidal 700603. seems promote vitro unconventional combinations. Additional are warranted understand significance these observations.