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

2012, Antimicrobial Agents and Chemotherapy

ABSTRACTColistin resistance, although uncommon, is increasingly being reported among Gram-negative clinical pathogens, and an understanding of its impact on the activity of antimicrobials is now evolving. We evaluated the potential for synergy of colistin plus trimethoprim, trimethoprim-sulfamethoxazole (1/19 ratio), or vancomycin against 12 isolates ofAcinetobacter baumannii(n= 4),Pseudomonas aeruginosa(n= 4), andKlebsiella pneumoniae(n= 4). The strains included six multidrug-resistant clinical isolates,K. pneumoniaeATCC 700603,A. baumanniiATCC 19606,P. aeruginosaATCC 27853, and their colistin-resistant derivatives (KPm1, ABm1, and PAm1, respectively). Antimicrobial susceptibilities were assessed by broth microdilution and population analysis profiles. The potential for synergy of colistin combinations was evaluated using a checkerboard assay, as well as static time-kill experiments at 0.5× and 0.25× MIC. The MIC ranges of vancomycin, trimethoprim, and trimethoprim-sulfamethoxazole...