Macrophage Polarization Alters Postphagocytosis Survivability of the Commensal Streptococcus gordonii

Abstract

Oral streptococci are generally considered commensal organisms; however, they are becoming recognized as important associate pathogens during the development of periodontal disease as well as being associated with several systemic diseases, including as a causative agent of infective endocarditis. An important virulence determinant of these bacteria is an ability to evade destruction by phagocytic cells, yet how this subversion occurs is mostly unknown. Using as a model commensal oral streptococcus that is also associated with disease, we find that resistance to reactive oxygen species (ROS) with an active ability to damage phagosomes allows the bacterium to avoid destruction within macrophages. This ability to survive relies not only on the ROS resistance capabilities of the bacterium but also on ROS production by macrophages, with both being required for maximal survival of internalized bacteria. Importantly, we also show that this dependence on ROS production by macrophages for resistance has functional significance: intracellular survival increases when macrophages are polarized toward an activated (M1) profile, which is known to result in prolonged phagosomal ROS production compared to that of alternatively (M2) polarized macrophages. We additionally find evidence of the bacterium being capable of both delaying the maturation of and damaging phagosomes. Taken together, these results provide essential insights regarding the mechanisms through which normally commensal oral bacteria can contribute to both local and systemic inflammatory disease.

Bacteria Modify Candida albicans Hypha Formation, Microcolony Properties, and Survival within Macrophages

“…To test whether changes in killing and escape of C. albicans from macrophages after coinfection with bacteria may be a result of changes in phagosomal maturation or ROS production, we measured the maturation kinetics of C. albicans -containing phagosomes by the loss of EEA1 (a marker of early maturation) and the acquisition of LAMP1 or lysosome-chased dextran (markers of phagosomal maturation) ( 34 , 38 ). Coinfection of macrophages with C. albicans and either S. gordonii or P. aeruginosa did not change the rate of phagosomal maturation, as measured by the loss of EEA1 or the increase of dextran.…”

“… C. albicans hypha formation within macrophages is an escape mechanism to subvert phagosomal clearance ( 47 ). Similarly, P. aeruginosa and certain strains of S. gordonii can also resist phagosomal killing in macrophages by promoting autophagy or suppressing phagosomal maturation ( 34 , 48 ). Our results indicate that C. albicans survival in macrophages in the presence of S. gordonii or P. aeruginosa are not dependent upon changes in macrophage phagocytic uptake, phagosome maturation, or ROS production.…”

“…Macrophages were seeded in 12-well culture plates with cover glass (Azer Scientific) and activated as described above. Phagosomal maturation was measured ( 34 ) with some modifications. C. albicans and bacterial cells were counted, and added to macrophages at an MOIs of 1 and 10, respectively.…”

“…Despite the well-known relationships of C. albicans with S. gordonii and P. aeruginosa , it is unclear whether simultaneous phagocyte interactions with yeast and bacteria affects the subsequent survival of C. albicans . Phagocytosis of S. gordonii alone by activated macrophages can permit phagosomal disruption on maturation, resulting in increased bacterial survival ( 34 ), and P. aeruginosa can evade phagocytosis by modifying its motility ( 35 , 36 ). It is likely that cospecies interactions within phagocytes will further modify their survival.…”

Danger signals in oral cavity-related diseases

“…in the development of disease . While there is an essential role for the adherence of the traditional pathogens such as P. gingivalis to the commensal flora, there is emerging evidence for commensal‐host immune cell interactions changing during inflammation, with increased survival within phagocytes potentially leading to increased PAMP signaling within the phagocyte cytoplasm …”