Final answer:
Pus inside a pustule is primarily composed of dead pathogens, neutrophils, and tissue fluid, indicating an immune response to a bacterial infection. It can be observed in various suppurative skin infections such as impetigo.
Step-by-step explanation:
Pus, the fluid found inside a pustule, is largely composed of a collection of dead pathogens, neutrophils, and tissue fluid. Additionally, it may contain other bystander cells that have been caught in the immune response and killed by phagocytes at the site of infection. Pus is a classic sign of a suppurative (pus-producing) infection of the skin, such as impetigo, and can manifest in various types of skin lesions like acne, furuncles (boils), or carbuncles.
When examining pus under a microscope, one may identify the types of bacteria present, which can be used to determine the appropriate treatment. The presence of pus indicates a strong immune response to infection, where neutrophils are attracted to the infection site, phagocytize the pathogens, and their accumulated cellular debris becomes visible as pus.