%0 Journal Article %A Peck, Kyong Ran %A Kim, Min Ja %A Choi, Ji Young %A Kim, Hong Sun %A Kang, Cheol-In %A Cho, Yong Kyun %A Park, Dae Won %A Lee, Hee Joo %A Lee, Mi Suk %A Ko, Kwan Soo %T In vitro time-kill studies of antimicrobial agents against blood isolates of imipenem-resistant Acinetobacter baumannii, including colistin- or tigecycline-resistant isolates %D 2012 %J Journal of Medical Microbiology, %V 61 %N 3 %P 353-360 %@ 1473-5644 %R https://doi.org/10.1099/jmm.0.036939-0 %I Microbiology Society, %X The emergence of colistin or tigecycline resistance as well as imipenem resistance in Acinetobacter baumannii poses a great therapeutic challenge. The bactericidal and synergistic effects of several combinations of antimicrobial agents against imipenem-, colistin- or tigecycline-resistant A. baumannii isolates were investigated by in vitro time-kill experiments. Six imipenem-resistant A. baumannii blood isolates were examined in this study, including colistin- and tigecycline-susceptible, colistin-resistant but tigecycline-susceptible, and colistin-susceptible but tigecycline-resistant isolates. Time-kill studies were performed using five antimicrobial agents singly or in combinations (imipenem plus colistin, imipenem plus ampicillin-sulbactam, colistin plus rifampicin, colistin plus tigecycline, and tigecycline plus rifampicin) at concentrations of 0.5× and 1× their MICs. Only imipenem was consistently effective as a single agent against all six A. baumannii isolates. Although the effectiveness of combinations of 0.5× MIC antimicrobial agents was inconsistent, combination regimens using 1× MIC of the antimicrobial agents displayed excellent bactericidal activities against all six A. baumannii isolates. Among the combinations of 0.5× MIC antimicrobial agents, the combination of colistin and tigecycline showed synergistic or bactericidal effects against four of the isolates. This in vitro time-kill analysis suggests that antimicrobial combinations are effective for killing imipenem-resistant A. baumannii isolates, even if they are simultaneously resistant to either colistin or tigecycline. However, the finding that the combinations of 0.5× MIC antimicrobial agents were effective on only some isolates may warrant further investigation of the doses of combination agents needed to kill resistant A. baumannii. %U https://www.microbiologyresearch.org/content/journal/jmm/10.1099/jmm.0.036939-0