title: Enhanced efficacy of imipenem-colistin combination therapy against multiple-drug-resistant Enterobacter cloacae: in vitro activity and a Galleria mellonella model.
abstract: OBJECTIVE
  To investigate the in vitro and in vivo activity of imipenem-colistin combination against multidrug-resistant Enterobacter cloacae infections in order to determine whether it should be explored further.
  
  
  METHODS
  The antimicrobial activity of colistin alone and in combination with imipenem was assessed versus an imipenem-susceptible isolate, E. cloacae GN1059, or an imipenem-resistant strain, E. cloacae GN0791, isolated in Anhui, China. The potential synergy of imipenem-colistin was evaluated using a checkerboard assay, as well as static time-kill experiments at 1× and 2× minimum inhibitory concentration (MIC). A simple invertebrate model (Galleria mellonella) was developed to assess the in vivo efficacy of imipenem-colistin in treating E. cloacae infection.
  
  
  RESULTS
  In checkerboard assays, synergy (defined as a fractional inhibitory concentration index of ≤ 0.5) was observed between imipenem and colistin for both isolates tested. In time-kill assays, the combination of imipenem-colistin at 1× or 2× MIC resulted in complete killing of both strains. In the G. mellonella larvae model infected with lethal doses of E. cloacae, the combination therapy led to significantly increased survival of the larvae as compared with imipenem or colistin monotherapy alone (p < 0.05).
  
  
  CONCLUSIONS
  This is the first report demonstrating the efficacy of antimicrobial agents in the G. mellonella larvae model of infections caused by E. cloacae. Our study suggested that imipenem-colistin combination was highly active against E. cloacae both in vitro and in the simple invertebrate model, and provided preliminary in vivo evidence that such combination might be useful therapeutically.
authors.affiliation: Department of Infectious Disease, The First Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Haifei
authors.initials: H
authors.lastname: Yang
authors.affiliation: Department of Infectious Disease, The First Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Guosheng
authors.initials: G
authors.lastname: Chen
authors.affiliation: Department of Infectious Disease, The First Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Lifen
authors.initials: L
authors.lastname: Hu
authors.affiliation: Department of Molecular Biology, Institute of Bacterium Resistance, Anhui Medical University, Hefei, China; Department of Molecular Biology, Anhui Center for Surveillance of Bacterial Resistance, Hefei, China.
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Infectious Disease, The First Affiliated Hospital of Anhui Medical University, Hefei, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Cheng
authors.affiliation: Department of Infectious Disease, The First Affiliated Hospital of Anhui Medical University, Hefei, China; Department of Molecular Biology, Institute of Bacterium Resistance, Anhui Medical University, Hefei, China; Department of Molecular Biology, Anhui Center for Surveillance of Bacterial Resistance, Hefei, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Ye
authors.affiliation: Department of Infectious Disease, The First Affiliated Hospital of Anhui Medical University, Hefei, China; Department of Molecular Biology, Institute of Bacterium Resistance, Anhui Medical University, Hefei, China; Department of Molecular Biology, Anhui Center for Surveillance of Bacterial Resistance, Hefei, China; Department of Infectious Diseases, Chaohu Hospital of Anhui Medical University, Hefei, China. Electronic address: lijiabin948@vip.sohu.com.
authors.forename: Jiabin
authors.initials: J
authors.lastname: Li
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002681:China; D003091:Colistin / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects*; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D016972:Enterobacter cloacae / Q000187:drug effects / Q000302:isolation & purification; D004756:Enterobacteriaceae Infections / Q000188:drug therapy; D006801:Humans; D015378:Imipenem / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects; D007915:Lepidoptera / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D023421:Models, Animal; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D015378:Imipenem; D003091:Colistin
keywords: antimicrobial synergy; colistin; drug resistance; imipenem; insect infection model