Answer:
Wound infection occurs when the number of pathogenic organisms exceeds the ability of local tissue defenses to combat them. For most bacterial species this number is 105/gm tissue, although for beta-hemolytic strep, wound problems may occur at lower numbers. Infection decreases tissue pO2 and increases collagenolysis, prolonging the inflammatory phase. In the presence of significant infection, leukocyte chemotaxis and migration, phagocytosis, and intracellular killing are decreased. Excessive bacterial colonization impairs angiogenesis and epithelialization. The granulation tissue of infected wounds is more edematous, somewhat hemorrhagic, and more fragile. Heavy contamination promotes collagenase activity through the action of microbial collagenase and endotoxins capable of cleaving the collagen molecule, ultimately resulting in decreased wound strength and contraction.