What is an example of a microorganism that can act as a pathogen?

Bacteria are single-celled microorganisms that can cause diseases in humans, animals, and plants, making them a prime example of pathogens. Pathogens are defined as organisms that can cause illness or disease, and bacteria fall into this category due to their ability to multiply and produce toxins or viruses that disrupt normal bodily functions.

In contrast, the other options do not qualify as pathogens. Dust is composed of tiny particles and does not inherently possess the biological properties needed to cause disease. Proteins are large biological molecules that perform various functions in the body but are not alive or capable of initiating disease processes on their own. Light, while essential for various biological processes, does not contain any living organisms and cannot act as a pathogen. Thus, bacteria effectively represent microorganisms that contribute to infections and illnesses.