The microbe that causes an infection or disease is most commonly referred to as the , or causative, agent.

The microbe that causes an infection or disease is most commonly referred to as the pathogen, or causative agent. Pathogens can take various forms, including bacteria, viruses, fungi, and parasites. Each type of pathogen has its own mechanisms of infection and ways of causing disease in the host.

For instance, bacteria are unicellular organisms that can reproduce rapidly and may produce toxins harmful to the host. Viruses, on the other hand, are much smaller and require a host cell to replicate, often leading to cellular damage or death. Fungi can cause infections by invading tissues and can be particularly problematic in immunocompromised individuals. Parasites can live on or in hosts, drawing nutrients at the host's expense, which can lead to malnutrition or other health issues.

Understanding the role of these pathogens is crucial in fields like medicine, epidemiology, and public health, as it helps in developing effective treatments and preventive measures against infectious diseases.