Which statement best defines a pathogen in the context of foodborne illness?

• A. Only bacteria that grow on food and produce visible spoilage and unpleasant smell.
• B. Any nonliving particle or chemical contaminant in food that alters flavor but does not cause disease.
• C. A macroscopic organism like a rodent or insect that physically contaminates food by contact, but not a microorganism.
• D. A microorganism (such as a bacterium, virus, or parasite) that can cause disease when transmitted by food or water.

Answer: (D)