Which microorganism is known to cause illness but does not reproduce on food?

The correct answer is viruses. Unlike bacteria and parasites, which can reproduce in food and cause illness through contamination, viruses do not multiply outside a host. They require a living host to replicate. When food is contaminated with viruses, they can cause illness upon ingestion, but they do not grow or reproduce on the food itself. This characteristic distinguishes viruses from other microorganisms such as bacteria and parasites, which can thrive in food environments and increase in number, posing additional risks. Fungi, while capable of growth on food, typically do not cause the same types of illness associated with foodborne viruses.