What characteristic differentiates a pathogen from a non-pathogen?

The characteristic that differentiates a pathogen from a non-pathogen is that pathogens cause disease in a host organism. Pathogens are defined by their ability to infect a host and lead to various disease manifestations, contributing to a range of health issues in multiple organisms, including humans.

A key point is that while all pathogens possess this damaging capability, non-pathogens do not cause disease; instead, they can be harmless or even beneficial to the host. This fundamental behavioral difference is what sets pathogens apart and makes understanding their characteristics crucial in fields like microbiology, infectious disease control, and public health. Other aspects, such as being multicellular or specific environmental needs, do not inherently define a microorganism as a pathogen since many pathogens are unicellular, adaptable, and can thrive in varied environments. Moreover, size is not a reliable distinguishing factor as pathogens can vary widely in size, just like non-pathogens.