What is defined as the invasion of the body by pathogenic microorganisms?

The term that best defines the invasion of the body by pathogenic microorganisms is "infection." Infections occur when these harmful microorganisms, such as bacteria, viruses, or fungi, enter the body, multiply, and begin to cause disease or illness. This process can trigger an immune response, leading to the various clinical signs and symptoms associated with infections, such as fever, pain, and inflammation.

In contrast, the concept of inflammation refers to the body's response to injury or infection, characterized by redness, heat, swelling, and pain, but it does not specifically denote the invasion by pathogens. Contamination typically refers to the presence of unwanted organisms or substances, not necessarily implying that they have invaded the body or caused disease. Contagion is related to the transmission of diseases from one individual to another, rather than the initial invasion of pathogens. Thus, the correct answer highlights the specific process of pathogenic invasion that leads to disease.