What term refers to the lessening of virulence in a microorganism?

The term that refers to the lessening of virulence in a microorganism is attenuation. In microbiology, attenuation involves a deliberate process where pathogens are weakened or modified so that they lose their ability to cause disease. This is significant in the development of vaccines, where an attenuated form of a virus or bacterium can stimulate an immune response without causing the actual disease.

By reducing the virulence, the microorganisms used in vaccines can effectively prepare the immune system to fight off more virulent forms of the pathogen in real-life exposures. This concept is critical in microbiology and immunology, as it allows for the safe prevention of diseases while eliciting a protective immune response.

The other terms, such as immunization, pathogenicity, and infection, are related concepts but do not specifically describe the process of reducing virulence. Immunization refers to the process of becoming immune through vaccination or exposure. Pathogenicity defines the ability of a microorganism to cause disease, and infection indicates the invasion and multiplication of pathogens in the host. Each of these concepts plays a role in understanding disease processes and prevention, but attenuation specifically denotes the reduction of pathogenic potential.