Sub-Projects of SFB 535
Invasion and Replication Strategies of Pathogenes
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SP B14

Prof. Dr. T. Chakraborty

Dr. Torsten Hain
Institut für Med. Mikrobiologie Justus-Liebig-Universität, Gießen


Listeria monocytogenes is a Gram-positive, food-borne microorganism responsible for invasive infections with a high overall mortality. After consumption of contaminated food products the bacteria enter the gastrointestinal tract, cross the gastrointestinal barrier and spread via the lymph and the blood to distant tissues and organs (e.g. liver, spleen, brain and gall bladder). In the process of infection the bacterium can cross the placental and blood brain barrier to cause the clinical symptoms of listeriosis, which often manifest as meningitis, meningoencephalitis, septicaemia, abortion, prenatal infection (Granulomatosis infantiseptica) and also gastroenteritis. The most impressive property of the bacterium is its ability to invade into and replicate within different nonphagocytic and phagocytic cell types.
We determined whole genome transcription profiling to examine the stress-induced SigB regulon and the intracellular growth expression profile of L. monocytogenes. Murine macrophages were infected with L. monocytogenes the expression profile of L. monocytogenes inside the vacuolar and the cytosolic environments were examined in detail. We found that ~17% of the total genome was mobilised (301 up-regulated and 182 down-regulated genes) to enable adaptation to intracellular growth including genes which are organised in different regulons (PrfA, CtsR, HrcA, SigB RpoN and OhrR).
(A) Among these intracellular induced genes we found the btlB gene locus, which is involved in the degradation of xenobiotic bile acid, to be highly up-regulated. Characterisation of this chromosomal region will allow us novel insights of this survival strategy of the intracellular pathogen. It is currently known that L. monocytogenes can persist within the murine gall bladder for days to avoid the cellular immune response of the host.
(B) To explore the effect of the enhanced host immune response on L. monocytogenes we have planned to investigate the intracellular expression profile of the bacterium after infection of IFN-?-activated macrophages.
(C) For L. monocytogenes it is known that the bacterium can invade in invertebrates such as Drosophila melanogaster. We would like to determine the listerial gene repertoire, which is important for intracellular survival and replication within Drosophila-S2 cells. Comparative analysis will allow us to identify the common gene set responsible for infection in invertebrates and vertebrates, respectively.
(D) Finally, we wish to apply the transposon site hybridisation (TraSH) technique to identify essential genes of the pathogenic bacterium, which are meaningful for intracellular survival in IFN-? activated macrophages and Drosophila-S2 cells followed by a functional characterisation of those essential target genes
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