Mykobakterielle Infektionen: Molekulargenetik, Protektion, Pathogenese und Membran-vermittelte Therapieresistenz. Teilprojekt: Siderophore als Antibiotikavektoren bei mykobakteriellen Infektionen Schlussbericht

Many drugs are hindered in the penetration of the mycobacterial cell envelope and the access to intracellular targets. Reduced target affinity, inactivating enzymes and efflux contribute to the resistance as well. Increased influx and higher intrinsic concentrations of drugs would act against these mechanisms. The high affinity iron aquisition systems provide an useful basis for active uptake of drugs. In order to select siderophores as possible vectors for drugs, more details of mycobacterial iron sequestering mechanisms have to be elucidated. The endogenous transport system of mycobacteria is characterized by iron ligand exchange between extracellular exochelin and membrane associated mycobactin. However, transport of the siderophore into the cell interior is an essential prerequisite for siderophore drug vectors. We have isolated and characterized exochelin and mycobactin negative mutants from fast growing mycobacteria as screening models for siderophore vectors for use in efficient growth promotion experiments. ["5"5Fe] transport experiments as well as in vivo Moessbauer and ESR spectroscopy confirmed the results of this screening. In contrast to citrate, ferricrocin and rhizoferrin were shown to transport iron without mycobactin mediated ligand exchange. Mycobactin doesn't represent the iron storage compound in any of the above transport systems. Iron transport experiments with citrate provided for the first time direct evidence for a metal transfer to membrane bound mycobactin. However, the ultimate destination of iron is a bacterioferritin comparable to that in E.coli. The ferritin found following rhizoferrin mediated iron uptake exhibits different parameters. Following ferricrocin mediated uptake, the iron is converted to a ferric storage component, which is not characterized so far. The studies provide evidence for independent and individuell iron transport pathways mediated by exogenous siderophores. These new findings, the mutants and the methods developed are useful for further investigations up to the synthesis of new therapeutics. (orig.)SIGLEAvailable from TIB Hannover: F98B190+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman