Investigating intracellular persistence of Staphylococcus aureus within a murine alveolar macrophage cell line

Abstract

Objective: Staphylococcus aureus is a particularly difficult pathogen to eradicate from the respiratory tract. Previous studies have highlighted the intracellular capacity of S.aureus in several phagocytic and non-phagocytic cells. The aim of this study was to define S.aureus interaction within a murine alveolar macrophage cell line.Methods: Cell line MH-S was infected with Newman strain. Molecular mechanisms involved in phagocytosis were explored. To assess whether S.aureus survives intracellularly quantitative (gentamicin protection assays and bacterial plating) and qualitative analysis (immunofluorescence microscopy) were performed. Bacterial colocalization with different markers of the endocytic pathway was examined to characterize its intracellular trafficking.Results: We found that S.aureus uptake requires host actin polymerization, microtubule assembly and activation of phosphatidylinositol 3-kinase signaling. Time course experiments showed that Newman strain was able to persist within macrophages at least until 28.5 h post infection. We observed that intracellular bacteria are located inside an acidic subcellular compartment, which co-localizes with the late endosome/lysosome markers Lamp-1, Rab7 and RILP. Colocalization counts with TMR-dextran might reflect a balance between bacterial killing and intracellular survival.Conclusions: This study indicates that S.aureus persists and replicates inside murine alveolar macrophages, representing a privileged niche that can potentially offer protection from antimicrobial activity and immunological host defense mechanisms.

In or out: Phagosomal escape ofStaphylococcus aureus

“…SaCP maturation quickly acquires the late phagosomal marker lysosome‐associated membrane protein‐1 (LAMP‐1) and Rab7. LAMP‐1 positivity and acidification of SaCP seem to be independent of host species and cell type (see, for instance, Kubica et al, ; Giese et al, ; Lâm et al, ; Grosz et al, ; Flannagan, Heit, & Heinrichs, ; Tranchemontagne, Camire, O'Donnell, Baugh, & Burkholder, ; Jubrail et al, ; Lacoma et al, ) indicating that S . aureus does not interfere with initial phagosomal maturation.…”

“…Also, a study on murine alveolar macrophages indicated that acidic phagosomal pH was not detrimental for S . aureus survival because bacteria were recovered in decreased numbers from cells treated with the v‐ATPase inhibitor bafilomycin (Lacoma et al, ).…”

“…This is supported by other studies, which show that bacterial replication is impaired during the first day of infection during which many bacteria succumb to the antimicrobial host cell response, yet macrophages ultimately fail in controlling S . aureus (Flannagan et al, ; Lacoma et al, ; Tranchemontagne et al, ). Following bacterial replication, macrophages die by pathways reminiscent of apoptotic as well as necroptotic/necrotic cell death, thereby releasing bacteria (Flannagan et al, ; Flannagan et al, ), which will be phagocytosed by other macrophages leading to a continuous infection cycle (Jubrail et al, ).…”

Nanodelivery strategies for the treatment of multidrug‐resistant bacterial infections

“…aureus , used to be considered as an extracellular bacterium; however, accumulating evidence suggests that S . aureus can invade and survive in either professional or nonprofessional phagocytes, including keratinocytes, endothelial cells, epithelial cells, fibroblast, and osteoblasts (Lacoma et al, ; Garzoni et al, ; Hanses et al, ; Reott et al, ). The adhesion of S .…”

“…Whilst inside these vacuoles, K. pneumoniae promotes activation of Akt to arrest phagosome maturation and avoid fusion into lysosomes, which would otherwise result in destruction. Another ESKAPE pathogen, S. aureus, used to be considered as an extracellular bacterium; however, accumulating evidence suggests that S. aureus can invade and survive in either professional or nonprofessional phagocytes, including keratinocytes, endothelial cells, epithelial cells, fibroblast, and osteoblasts (Lacoma et al, 2017;Garzoni et al, 2009;Hanses et al, 2011;Reott et al, 2008). The adhesion of S. aureus to the host cell surface results in cytoskeletal rearrangement to allow S. aureus to move into cells.…”