Final answer:
N. meningitidis causes hemorrhagic bruises through its LOS endotoxin, causing blood vessel damage and blood leakage.
Step-by-step explanation:
N. meningitidis causes the hemorrhagic (purple) bruises seen on the skin through the action of its virulence factors, especially the LOS (lipooligosaccharide) endotoxin, which is a component of the bacterial cell wall. This endotoxin causes an inflammatory response that leads to the disruption of endothelial cells in capillaries and small veins. As a result, blood vessels are damaged, and tiny blood clots form, leading to blood leaking into surrounding tissue and causing the characteristic hemorrhagic rash. If the infection progresses into sepsis, the impact of virulence factors such as LOS endotoxin increases, causing exacerbated hemorrhage and clot formation, potentially leading to disseminated intravascular coagulation, shock, and even death.