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Sasha Rose Mentor: Dr. Luiz Bermudez OSU College of Veterinary Medicine Department of Biomedical Sciences Using In Vivo Expression Technology to Identify Mycobacterium avium Genes Expressed during Intracellular Infection in Dendritic Cells and Mice
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Relevance Mycobacterium avium Closely related to M. leprae and M. tuberculosis Common opportunistic infection in AIDS patients Usually infects gastrointestinal or respiratory system Treatment includes a combination of antibiotics http://www.hain-lifescience.com/images/avium.jpg
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Background Mycobacterium avium Common genetic profiles Free living in environment Invasion of host cell Survival in host cell Genes turned on while in host cell Suppress immune response of the host Maintenance of vacuole Mineral transport Difficult to identify What genes do what functions Where on the genome the genes are located
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In vivo expression technology (IVET) A technique used to identify the virulence genes in a bacterium when expressed in a living cell Goal – To establish an IVET system suitable for screening M. avium genes required for survival in a host environment, using quinolone resistance as a selection marker
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Quinolones Broad spectrum antibiotics Inhibit the GyrA subunit of the DNA gyrase enzyme DNA gyrase enzyme Type II topoisomerase Crucial for DNA replication Relieves tension when DNA is wound too tightly GyrA subunit Binds/breaks DNA made from the gyrA gene
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Mutant gyrA gene Single point mutation Creates quinolone resistant GyrA subunits Previous work Genome broken into thousands of fragments Kanamycin marker Transformed into wild type M. avium “GyrA” bacteria PLDG13-GyrA plasmid promoterless mutant gyrA gene random fragment
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Hypothesis A bacterium that survives the quinolone treatment will possess a fragment that contains a promoter sequence for a gene that was expressed while in the host cell
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Methods Part I - using IVET to select bacteria Dendritic cells-early infection Mice-established infection Part II - screening and identifying genes http://www.unis.org/UNIScienceNet/DendriticC ell_400.jpg
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Obtaining Dendritic Cells whole blood centrifuge withdraw middle layer wash 3 times, re- suspend with RPMI medium add cytokines human IL-4 and GM-CSF; allow 5 day growth at 37°C mature dendritic cells monocytes
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Using IVET in Dendritic Cells incubate for 1 hour wash cells and begin 4, 24, or 48 hour time point treat with moxifloxacin at 8µg/mL; allow 24 hours lyse cells and plate bacteria on Petri dishes dendritic cell infect with GyrA bacteria; 1 well for each time point infected with wild type MAC 104
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Using IVET in Mice C57BL/6 20 total-4 cages Bacteria administered orally via gavaging Cage 1 = wild type MAC 104 Cages 2-4 = GyrA
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Using IVET in Mice 10 week system Kanamycin injections daily for first 3 weeks Selecting for plasmid Cages 2-4 Moxifloxacin injections daily for last 7 weeks Cages 1-3 100mg/kg Mice were sacrificed in 3 groups
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Using IVET in Mice Necropsies were performed on all of the mice Lung, liver, spleen, and mesenteric tissue samples were homogenized Samples were plated on Petri dishes
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Bacterial Survival 2 morphologies Yellow White Each colony should have a unique fragment
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Screening and Identifying Genes Pick off individual colony; isolate plasmid Use PCR to amplify the fragment Use gel electrophoresis to screen PCR products 228bp gyrAfragment Added together equals 228 bp
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Results Quinolone Selection Screened over 60 colonies Double band pattern No difference between samples PCR reagent control = negative Wild type controls survived treatment 728bp 228bp
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Mouse toxicity/health Multiple mice - fibrinous exudate 2 deaths – unknown cause 1 mouse euthanized early because of severe abdominal inflammation Ended experiment 1 week early Loss of activity Abdominal inflammation
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Discussion Wild type survival - insufficient selection occurred Dendritic Cells Very short treatment time Mice Poor absorption of moxifloxacin from the intraperitoneal space Mouse toxicity/Health Health problems not associated with M. avium Cage 4 mice received no moxifloxacin
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Dr. Luiz Bermudez and the rest of the lab Oregon State University College of Veterinary Medicine Howard Hughes Medical Institute Dr. Kevin Ahern Acknowledgements
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