What characterizes a pathogen?

A pathogen is characterized as a microorganism that can cause disease. This definition encompasses a variety of organisms, including bacteria, viruses, fungi, and parasites, which have mechanisms to invade host organisms and disrupt normal physiological functions. Pathogens can lead to infections, illness, and even death, depending on the virulence of the microorganism and the susceptibility of the host.

The distinction between pathogens and beneficial bacteria is crucial; not all microorganisms are harmful, and many play essential roles in processes such as digestion and immune function. Additionally, while some pathogens are consistently harmful, not all cause disease in every host, as the outcome often depends on host factors like immune response. Lastly, not all bacteria found in the human body are pathogenic; many are part of the normal microbiota that contribute to health and well-being. Hence, the identification of a pathogen specifically relates to its capability to cause disease.