Which is not listed as one of the four types of microbes?

• A. Prions
• B. Bacteria
• C. Parasites
• D. Fungi

Answer: (A)

Prions are not considered a microbe because they are simply misfolded proteins that cause disease and lack both nucleic acids and cellular structure. Microbes are typically grouped into bacteria, viruses, fungi, and parasites, each with genetic material or cellular organization. Bacteria are unicellular organisms with DNA and cell walls; fungi include yeasts and molds; parasites are organisms that live on or in a host and include protozoa and helminths; viruses are infectious agents that contain genetic material but lack cellular machinery and must hijack a host to replicate. Prions, by contrast, do not have DNA or RNA and don’t replicate on their own; they propagate by converting normal host proteins into the misfolded prion form. That’s why prions aren’t listed among the four types of microbes.