Staphylococcus aureus Induces Hypoxia and Cellular Damage in Porcine Dermal Explants

Abstract

fWe developed a porcine dermal explant model to determine the extent to which Staphylococcus aureus biofilm communities deplete oxygen, change pH, and produce damage in underlying tissue. Microelectrode measurements demonstrated that dissolved oxygen (DO) in biofilm-free dermal tissue was 4.45 ؎ 1.17 mg/liter, while DO levels for biofilm-infected tissue declined sharply from the surface, with no measurable oxygen detectable in the underlying dermal tissue. Magnetic resonance imaging demonstrated that biofilm-free dermal tissue had a significantly lower relative effective diffusion coefficient (0.26 ؎ 0.09 to 0.30 ؎ 0.12) than biofilm-infected dermal tissue (0.40 ؎ 0.12 to 0.48 ؎ 0.12; P < 0.0001). Thus, the difference in DO level was attributable to biofilm-induced oxygen demand rather than changes in oxygen diffusivity. Microelectrode measures showed that pH within biofilm-infected explants was more alkaline than in biofilm-free explants (8.0 ؎ 0.17 versus 7.5 ؎ 0.15, respectively; P < 0.002). Cellular and nuclear details were lost in the infected explants, consistent with cell death. Quantitative label-free shotgun proteomics demonstrated that both proapoptotic programmed cell death protein 5 and antiapoptotic macrophage migration inhibitory factor accumulated in the infected-explant spent medium, compared with uninfected-explant spent media (1,351-fold and 58-fold, respectively), consistent with the cooccurrence of apoptosis and necrosis in the explants. Biofilm-origin proteins reflected an extracellular matrix-adapted lifestyle of S. aureus. S. aureus biofilms deplete oxygen, increase pH, and induce cell death, all factors that contribute to impede wound healing.

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

“…Interestingly, in a murine model of acute colitis, neutrophils actively contributed to the hypoxic microenvironment by depletion of molecular oxygen through NADPH oxidase activity and, hence, induced stabilisation of epithelial HIF [29]. Furthermore, Staphylococcus aureus was shown to deplete oxygen in a skin infection model, and biofilm-induced oxygen demand made the underlying dermal tissue anoxic [30]. Hypoxia impedes wound healing, and has been shown to impair clearance of inhaled S. aureus, though not Proteus mirabilis, in a mouse model of lung infection [31].…”

“…aureus infection often establishes a hypoxic environment; for example staphylococcal biofilms induce hypoxia in dermal tissue, impairing wound healing [30]. A second example relates to osteomyelitis; healthy bone is intrinsically hypoxic, and further decreases in skeletal oxygen concentration upon S. aureus infection were revealed by intravital oxygen monitoring [83].…”

Trade-offs between microbiome diversity and productivity in a stratified microbial mat

“…Samples were positioned on agar in 15 mm nuclear magnetic resonance tubes, and degassed under dark conditions to remove bubbles prior to interrogation. ParaVision v5.1 was used to run chemical shift selective imaging (mic chess) (Ha et al, 2015;Lone et al, 2015a) and 2D diffusion-mapping experiments (DtiStandard) (Lone et al, 2015b), both with a resolution of 78 × 156 μm. Scalar irradiance (photosynthetically active radiation) profiles were measured in quadruplicate with isotropic photosynthetically active radiation microsensors with spherical 70 μm diameter tips (Zensor, Åls-gårde, DK) fiber optically connected to a spectrophotometer (USB2000+-ES, Ocean Optics, Dunedin, FL, USA) and inter-calibrated against a radiometer (LI-250A and LI-COR Quantum sensor, LI-COR Biosciences, Lincoln, NE, USA) (Lassen et al, 1992).…”

Colonization of Epidermal Tissue by Staphylococcus aureus Produces Localized Hypoxia and Stimulates Secretion of Antioxidant and Caspase-14 Proteins

“…Porcine ears were obtained from a local abattoir at the time that private client animals were being butchered (no purpose-bred, purchased, or live animals were used for this study). The ears were stored on ice, and within an hour of collection, epidermal explants were prepared in a way similar to that described by Lone et al for dermal explant preparation (19). The explants were cleaned with water, dried with paper towels, and lightly sprayed with 70% ethanol.…”

“…Oxygen is the preferred terminal electron acceptor for ATP synthesis in most bacterial pathogens (18), and it could be locally depleted in the epidermis if a large number of bacteria are present. We have previously shown that S. aureus biofilms grow rapidly on dermal tissue with quick depletion of oxygen in the underlying tissue (19). Consequently, we hypothesized that colonization of epidermis with S. aureus leads to formation of localized biofilm communities that subsequently deplete oxygen from the underlying epidermal tissue.…”