In vitro activities of tigecycline, ertapenem, isepamicin, and other antimicrobial agents against clinically isolated organisms in Taiwan

This study evaluated the in vitro activities of tigecycline, ertapenem, isepamicin, and other comparators against 861 bacterial isolates recovered from patients treated in three major teaching hospitals in 2003. MICs to antimicrobial agents were determined by the agar dilution method. High rates of oxacillin resistance (58%) in Staphylococcus aureus (60 isolates), and vancomycin resistance (21%) and quinupristin-dalfopristin nonsusceptibility (39%) in Enterococcus faecium (34 isolates) were found. Carbapenems had excellent in vitro activities (≥98% susceptibility) against the 419 isolates of Enterobacteriaceae, with the MIC₅₀ and MIC₉₀ of imipenem, meropenem, and ertapenem being 0.25 and 4 mg/L, 0.03 and 0.12 mg/L, and 0.03 and 0.5 mg/L, respectively. For, Pseudomonas aeruginosa (74 isolates) and Burkholderia cepacia (21 isolates), meropenem (MIC₉₀, 0.25, 2, and 4 mg/L, respectively) had better in vitro activities than imipenem (MIC ₉₀, 8, 4, and 32 mg/L, respectively) and ertapenem (MIC₉₀, 0.5, > 32, and 32 mg/L, respectively). Isepamicin had a similar activity with amikacin against all Enterobacteriaceae, Pseudomonas aeruginosa, B. cepacia, and Acinetobacter baumannii, except for C. freundii isolates in which isepamicin had an eight-fold activity better than amikacin. Tigecycline had excellent in vitro activities against all isolates tested (MIC₉₀, ≤1 mg/L) including 14 pandrug-resistant A. baumannii isolates (MICs, 1-4 mg/L), except for Proteus mirabilis (59 isolates; MIC₉₀, 8 mg/L), Bacteroides fragilis (60 isolates; MIC₉₀, 8 mg/L), P. aeruginosa (MIC₉₀,16 mg/L), and B. cepacia (21 isolates; MIC₉₀, 16 mg/L). Tigecycline, carbapenems, and isepamicin exhibited better or comparable in vitro activities against a wide spectrum of commonly encountered bacteria than other comparator antimicrobials and may represent therapeutic options for infections due to multidrug-resistant pathogens.