A combination of levofloxacin and colistin is bactericidal against colistin-susceptible Acinetobacter baumannii
Over the last two decades, Acinetobacter baumannii has become of increasing significance because of its remarkable ability to cause outbreaks of infections which rapidly acquire resistance to almost all currently used antibiotics. The only antibiotics that have remained consistently active in vitro against multidrug resistance to A. baummannii are polymixins and tigecycline. However, recent data suggest that levofloxacin may be active against MDR-AB if used in combination with colistin. This study was carried out by investigators in several departments of Anhui Medical University and the Anhui Centre for Surveillance of Bacterial Resistance, Hefei, PR China. The investigators used a simple invertebrate Galleria mellonella model to examine the in vivo activity of levofloxacin alone or in combination with colistin. The Galleria mellonella model is widely used to test the pathogenic effects of microorganism because it shares many of the advantages of mammalian models but is free of ethical and logistic constraints. The drug doses were selected to be representative of those used to treat human infection with colistin being given at a dose of 2.5 mg/kg and levofloxacin at 6.7 mg/kg. Treatments were given only once.
A synergistic effect was indeed observed between levofloxacin and colistin but the authors advise caution because of the limited nature of the isolates used. In addition, they say that their conclusions need further confirmation, particularly to show that the results will hold true for longer than 72 hours. To do this they recommend further studies using mammalian models.
J Microbiol Immunol Infect. 2015 Nov 26. pii: S1684-1182(15)00907-X. doi: 10.1016/j.jmii.2015.10.010. [Epub ahead of print]
Source : http://www.ncbi.nlm.nih.gov/pubmed/26725481?dopt=Abstract