A Murine Skin Wound Infection Model to Study the Immune Response against a Bacterial Pathogen

Take an anesthetized mouse engineered to express a fluorescent protein in neutrophils. Shave the dorsum and create a circular cut. Excise the cut skin to reveal the fascia — a connective tissue layer underneath.

Take a syringe containing a suspension of Staphylococcus aureus — a pathogenic bacterium — genetically modified to produce bioluminescence. Inject the suspension between the fascia and the underlying tissue generating a localized wound infection.

The pattern recognition receptors on stromal cells in the fascia recognize the pathogen-associated molecular patterns on the bacteria. This binding induces the release of pro-inflammatory cytokines and chemoattractants — resulting in inflammation.

Chemoattractants recruit circulatory neutrophils at the infection site. Incoming neutrophils engulf the bacteria into a phagosome that fuses with cytoplasmic granules, causing antimicrobial peptide release.

NADPH oxidase — an enzyme complex — assembles on the phagosome membrane and produces reactive oxygen species or ROS. The antimicrobial peptides and ROS cause bacterial degradation.

As a counter-response, the bacteria secrete virulence factors that permeabilize the neutrophil membrane, causing cell lysis. The bacteria also release enzymes for the deposition of fibrin to avoid phagocytosis.

The immune response leads to an abscess — a fibrin capsule containing bacterial cells, neutrophils, and dead cells.

Record the neutrophil fluorescence and bacterial bioluminescence to visualize the bacteria-neutrophil interaction.