Which microorganisms require a living host to grow and can be transmitted through food?

The correct choice is that parasites require a living host to grow and can be transmitted through food. Parasites are organisms that live on or inside another organism (the host) to obtain their nutrients. They depend on the host for their lifecycle and cannot survive or multiply without it.

In the context of foodborne illnesses, certain parasites can be transmitted to humans through contaminated food or water. For instance, parasites like Giardia or Trichinella can cause infections when food or water contaminated with their eggs or larvae is ingested.

While viruses, like hepatitis A or norovirus, can also be transmitted through food, they do not require a living host to grow; they rely on host cells to replicate after infection. Bacteria and fungi are distinct in that they can grow and multiply independently in food, as they do not need a living host. Thus, the focus on the need for a living host to grow directly identifies parasites as the correct answer.