Deciphering the Intracellular Fate ofPropionibacterium acnesin Macrophages

Abstract

Propionibacterium acnesis a Gram-positive bacterium that colonizes various niches of the human body, particularly the sebaceous follicles of the skin. Over the last years a role of this common skin bacterium as an opportunistic pathogen has been explored. Persistence ofP. acnesin host tissue has been associated with chronic inflammation and disease development, for example, in prostate pathologies. This study investigated the intracellular fate ofP. acnesin macrophages after phagocytosis. In a mouse model ofP. acnes-induced chronic prostatic inflammation, the bacterium could be detected in prostate-infiltrating macrophages at 2 weeks postinfection. Further studies performed in the human macrophage cell line THP-1 revealed intracellular survival and persistence ofP. acnesbut no intracellular replication or escape from the host cell. Confocal analyses of phagosome acidification and maturation were performed. Acidification ofP. acnes-containing phagosomes was observed at 6 h postinfection but then lost again, indicative of cytosolic escape ofP. acnesor intraphagosomal pH neutralization. No colocalization with the lysosomal markers LAMP1 and cathepsin D was observed, implying that theP. acnes-containing phagosome does not fuse with lysosomes. Our findings give first insights into the intracellular fate ofP. acnes; its persistency is likely to be important for the development ofP. acnes-associated inflammatory diseases.