Pathogens often first encounter physical barriers such as the skin and mucous membranes. These barriers consist of tightly packed epithelial cells that act as a first line of defense. However, pathogens have evolved several strategies to breach these barriers. For example: - Mechanical damage: Wounds or abrasions can break the integrity of the skin, allowing pathogens to enter. - Enzymatic degradation: Some bacteria secrete enzymes like collagenase and hyaluronidase to degrade extracellular matrix components. - Cellular invasion: Certain pathogens can directly invade epithelial cells using specialized structures like pili or through endocytosis.
