Topic overview

Start with the big picture

Microbes are not one uniform category: some are cellular, while viruses and prions are acellular. Bacteria and archaea are prokaryotes; fungi and parasitic organisms are eukaryotes. The groups also differ in structure and reproduction—for example, bacteria divide by binary fission, viruses use host-cell machinery, and fungi may occur as yeasts, molds, or dimorphic forms. Other organisms covered include plant-infecting viroids, protozoa, helminths, ectoparasites, and algae, which may have relevance through toxin production. Comparing these categories by size, cellular organization, genetic material, and replication offers a practical way to orient yourself before studying their clinical significance in greater depth.