Obligate

OBLIGATE (from the Latin obligatus - obligatory, necessary), a term used in biology and medicine to denote a property that is necessarily inherent to a given phenomenon, organism, or substrate. This term is especially common in microbiology and parasitology. The most common designations are: obligate parasites - microorganisms that are currently known only as parasites (as opposed to facultative parasites), obligate aerobes and anaerobes (see), i.e., microbes that develop only with access to oxygen or only in its absence. However, obligateness should be considered a relative concept: an obligate property under certain conditions may become non-obligate. For example, many obligate anaerobes still develop with a slight concentration of O₂ in the environment. Many parasites are considered obligate only because the conditions for their existence as saprophytes are not yet known. A whole series of so-called obligate parasites can be cultivated on artificial nutrient media outside the organism. Factors that are obligate in the development of any diseases mostly manifest their effect only in the presence of other favorable environmental or organismal factors. Under other conditions, they often can produce a completely different effect, distinct from the usual one.