Microbial Taxonomy

Microorganism classification while imperfect facilitates communication of concept.


A speculative phylogenetic tree diagram of all life forms, useful for our purposes. A more substantial one can be found here. [Image: Slide Player]

Host–Microbial Relationship

  • Symbiont: mutual benefit
  • Commensal: surface contact only (no disease)
  • Pathogen: macromolecular interaction (microbe in close contact with host immune defense)
    • frank pathogen — probable agent of disease
    • opportunistic pathogen — organism isolated from a host with impaired defences
    • non-pathogenic — organism that rarely cause disease


A non-mutual symbiotic relationship between species, where one species, the parasite, benefits at the expense of the other, the host.



Medically important fungi are of four phyla:

  • Ascomycota —sexual reproduction in a sack called an ascus (→ ascospores)
  • Basidiomycota — sexual reproduction in a sack called a basidium (→ basidiospores)
  • Zygomycota — sexual reproduction by gametes and asexual reproduction (→ zygospores)
  • Mitosporic Fungi [Fungi Imperfecti] — no recognizable form of sexual reproduction; includes most pathogenic fungi

Protista (protozoans)