# Microbe --- A **microbe** is a term for a very small being that is studied in the field of [[microbiology]]. Microbes come in two broad categories, cellular and non-cellular. Cellular microbes are [[bacteria]] and [[archaea]], [[fungi]] and [[protozoa]]. Non-cellular microbes are [[virus|viruses]]. Some of them can cause disease in humans and these are considered [[pathogen|pathogens]]. ## Symbiotic Relationships **Symbiotic relationships** are those where a microbes (or, *symbiote*) lives on or in another organism. Sometimes this relationship is is mutually beneficial, other times it can be quite deadly. ### Mutualism **Mutualism** is a type of symbiotic relationship where both the microbe (a [[normal microbiota]]) and the host organism benefit. For example [[Escherichia coli|E. coli]] that lives in our intestines that produce vitamin K for us, helps with digestion, and crowds out harmful bacteria. Another example of mutualism is how algae and fungus can come together to form a [[lichen]]. ### Commensalism **Commensalism** is a type of symbiotic relationship where the microbe (a [[normal microbiota]]) benefits while the host is unaffected. Some scientists think that there isn't really any such thing as commensalism, and that if you dig deep enough the host is always affected. For example, the Staphylococcus that lives on our skin. ### Parasitism **Parasitism** is a type of host symbiotic relationship where the microbe (a [[pathogen]]) benefits while the host is harmed. For example, Leoned's favorite *Nieserria ghonnerrhea*. ## Fighting Against Pathogens We don't like the microbes that can cause us harm. **[[Antimicrobial substances]]** are the biological enzymes that our [[immune system]] make naturally to fight against pathogens. **[[Antimicrobial drugs]]** are our human-made substances that we can use against pathogens. ___