What is the key distinction between a pathogen and a commensal organism?

The key distinction between a pathogen and a commensal organism lies in their relationship with the host and the result of that relationship. A pathogen is defined as an organism that has the ability to cause disease in its host. Pathogens can disrupt normal physiological functions, leading to illness and other negative health effects.

On the other hand, a commensal organism resides on or in a host without inducing harm. In fact, commensal organisms often play beneficial roles in maintaining the host's health, such as aiding in digestion or outcompeting potential pathogens for resources. Therefore, the primary characteristic that separates pathogens from commensal organisms is the ability of pathogens to cause disease, whereas commensals do not cause harm and may even provide benefits to the host. This relationship is crucial in understanding microbial ecology and the dynamics of host-microbe interactions.