title: Inducible control of virulence gene expression in Listeria monocytogenes: temporal requirement of listeriolysin O during intracellular infection.
abstract: We have constructed a lac repressor/operator-based system to tightly regulate expression of bacterial genes during intracellular infection by Listeria monocytogenes. An L. monocytogenes strain was constructed in which expression of listeriolysin O was placed under the inducible control of an isopropyl-beta-D-thiogalactopyranoside (IPTG)-dependent promoter. Listeriolysin O (LLO) is a pore-forming cytolysin that mediates lysis of L. monocytogenes-containing phagosomes. Using hemolytic-activity assays and Western blot analysis, we demonstrated dose-dependent IPTG induction of LLO during growth in broth culture. Moreover, intracellular growth of the inducible-LLO (iLLO) strain in the macrophage-like cell line J774 was strictly dependent upon IPTG. We have further shown that iLLO bacteria trapped within primary phagocytic vacuoles can be induced to escape into the cytosol following addition of IPTG to the cell culture medium, thus yielding the ability to control bacterial escape from the phagosome and the initiation of intracellular growth. Using the iLLO strain in plaque-forming assays, we demonstrated an additional requirement for LLO in facilitating cell-to-cell spread in L2 fibroblasts, a nonprofessional phagocytic cell line. Furthermore, the efficiency of cell-to-cell spread of iLLO bacteria in L2 cells was IPTG dose dependent. The potential use of this system for determining the temporal requirements of additional virulence determinants of intracellular pathogenesis is discussed.
authors.affiliation: Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, MA 02115-6092, USA.
authors.forename: Christina E
authors.initials: CE
authors.lastname: Dancz
authors.forename: Andrea
authors.initials: A
authors.lastname: Haraga
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Portnoy
authors.forename: Darren E
authors.initials: DE
authors.lastname: Higgins
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001427:Bacterial Toxins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D003603:Cytotoxins / Q000235:genetics / Q000378:metabolism*; D004269:DNA, Bacterial; D005347:Fibroblasts / Q000166:cytology / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D005818:Genetic Engineering; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006460:Hemolysin Proteins; D007424:Intracellular Fluid / Q000382:microbiology; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity; D051379:Mice; D008969:Molecular Sequence Data; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D003603:Cytotoxins; D004269:DNA, Bacterial; D006360:Heat-Shock Proteins; D006460:Hemolysin Proteins; C038705:hlyA protein, Listeria monocytogenes