title: Monocytes Are the Predominant Cell Type Associated withListeria monocytogenesin the Gut, but They Do Not Serve as an Intracellular Growth Niche.
abstract: After foodborne transmission of the facultative intracellular bacterial pathogenListeria monocytogenes, most of the bacterial burden in the gut is extracellular. However, we previously demonstrated that intracellular replication in an as yet unidentified cell type was essential for dissemination and systemic spread ofL. monocytogenesIn this article, we show that the vast majority of cell-associatedL. monocytogenesin the gut were adhered to Ly6Chimonocytes, a cell type that inefficiently internalizedL. monocytogenesWith bone marrow-derived in vitro cultures, high multiplicity of infection or the use of opsonized bacteria enhanced uptake ofL. monocytogenesin CD64-monocytes, but very few bacteria reached the cell cytosol. Surprisingly, monocytes that had upregulated CD64 expression in transition toward becoming macrophages fully supported intracellular growth ofL. monocytogenesIn contrast, inflammatory monocytes that had increased CD64 expression in the bone marrow of BALB/c/By/J mice prior toL. monocytogenesexposure in the gut did not supportL. monocytogenesgrowth. Thus, contrary to the perception thatL. monocytogenescan infect virtually all cell types, neither naive nor inflammatory Ly6Chimonocytes served as a productive intracellular growth niche forL. monocytogenes.These results have broad implications for innate immune recognition ofL. monocytogenesin the gut and highlight the need for additional studies on the interaction of extracellular, adherentL. monocytogeneswith the unique subsets of myeloid-derived inflammatory cells that infiltrate sites of infection.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine, Lexington, KY 40536.
authors.forename: Grant S
authors.identifier: 0000-0001-7945-8038
authors.initials: GS
authors.lastname: Jones
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine, Lexington, KY 40536 sarah.dorazio@uky.edu.
authors.forename: Sarah E F
authors.initials: SE
authors.lastname: D'Orazio
mesh_terms: D000818:Animals; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005434:Flow Cytometry; D007422:Intestines / Q000276:immunology* / Q000382:microbiology; D008089:Listeria monocytogenes / Q000276:immunology / Q000472:pathogenicity; D008088:Listeriosis / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D009000:Monocytes / Q000276:immunology*; D010587:Phagocytosis; D014774:Virulence