title: Inability to sustain intraphagolysosomal killing of Staphylococcus aureus predisposes to bacterial persistence in macrophages.
abstract: Macrophages are critical effectors of the early innate response to bacteria in tissues. Phagocytosis and killing of bacteria are interrelated functions essential for bacterial clearance but the rate-limiting step when macrophages are challenged with large numbers of the major medical pathogen Staphylococcus aureus is unknown. We show that macrophages have a finite capacity for intracellular killing and fail to match sustained phagocytosis with sustained microbial killing when exposed to large inocula of S. aureus (Newman, SH1000 and USA300 strains). S. aureus ingestion by macrophages is associated with a rapid decline in bacterial viability immediately after phagocytosis. However, not all bacteria are killed in the phagolysosome, and we demonstrate reduced acidification of the phagolysosome, associated with failure of phagolysosomal maturation and reduced activation of cathepsin D. This results in accumulation of viable intracellular bacteria in macrophages. We show macrophages fail to engage apoptosis-associated bacterial killing. Ultittop mately macrophages with viable bacteria undergo cell lysis, and viable bacteria are released and can be internalized by other macrophages. We show that cycles of lysis and reuptake maintain a pool of viable intracellular bacteria over time when killing is overwhelmed and demonstrate intracellular persistence in alveolar macrophages in the lungs in a murine model.
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.
authors.forename: Jamil
authors.initials: J
authors.lastname: Jubrail
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Morris
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.
authors.forename: Martin A
authors.initials: MA
authors.lastname: Bewley
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Stoneham
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.|Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK.
authors.forename: Simon A
authors.initials: SA
authors.lastname: Johnston
authors.affiliation: The Florey Institute, University of Sheffield, Sheffield, UK.|Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Foster
authors.affiliation: Department of Biomedical Sciences, University of Sheffield, Sheffield, UK.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Peden
authors.affiliation: Academic Unit of Clinical and Experimental Sciences, University of Southampton Medical School, Southampton, UK.
authors.forename: Robert C
authors.initials: RC
authors.lastname: Read
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.
authors.forename: Helen M
authors.initials: HM
authors.lastname: Marriott
authors.affiliation: Department of Infection and Immunity, University of Sheffield, Sheffield, UK.|The Florey Institute, University of Sheffield, Sheffield, UK.|Academic Directorate of Communicable Diseases, Sheffield Teaching Hospitals, Sheffield, UK.
authors.forename: David H
authors.initials: DH
authors.lastname: Dockrell
mesh_terms: D000818:Animals; D002470:Cell Survival; D004195:Disease Models, Animal; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology*; D051379:Mice; D050296:Microbial Viability; D010587:Phagocytosis; D011023:Pneumonia, Staphylococcal / Q000473:pathology*; D013211:Staphylococcus aureus / Q000276:immunology* / Q000502:physiology*
keywords: Staphylococci; antimicrobial; immunology; microbial-cell interaction