What type of microbes can infect animal and human cells, utilizing host cell sources?

The correct answer is the category of intracellular microbes. These are microorganisms that have the ability to invade and live within the cells of a host organism, which can include both animals and humans. By residing inside host cells, these microbes can take advantage of the host's cellular machinery and resources, such as nutrients, to grow and replicate. This capability often also allows them to evade certain immune responses that target extracellular pathogens.

Intracellular microbes encompass a variety of pathogens, including some bacteria (like Mycobacterium tuberculosis), viruses (like HIV and influenza), and protozoa (such as Plasmodium, which causes malaria). Their survival and replication within host cells can lead to chronic infections and produce specific immune responses.

Other categories mentioned, such as pathogenic microbes, refer broadly to those that cause disease, but not all are intracellular. Harmless microbes typically live without causing harm and do not exploit host cell systems for nutrients or replication. Extracellular microbes are those that exist outside of host cells and do not invade them, relying on different strategies to survive and propagate.