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Definition

Pathogenic refers to something that is capable of causing disease.

Etymology. "producing disease," 1852, from Fr. pathogénique, from Gk. pathos "disease" (see pathos) + Fr. génique "producing." Earlier pathogenetic (1838). Pathogen "a bacteria that produces disease" is an 1880 back-formation.

Discussion

Pathogenic Relations

There are rnany different types of pathogenic relations. These are generally described based on the activities of the pathogen

Older terminologv describing parasitism and pathoyenic relations:

1) Obligate parasite      - requires a living host to complete its life cycle.

2) Facultative parasite    - normally exists as a saprophyte, but may live parasitically.

3) Facultative saprophyte  - normally exists as a parasite, but may live as a saprophyte.

4) Obligate saprophyte     - only obtains nutrients from non-living carbon sources.

One limitation of this terminology is that it is based to a large extent on our ability to culture the organism in vitro (in culture; outside the host). Yet with increased study, organisms previously classified as obligate parasites can now be grown to varying degrees on artificial substrates.

 

These developments led to the expression of the above concepts using different terminology, as follows:

Newer/Modern terminology to describe symbiotic parasitic relationships:

1) Biotroph           - obtains nutrients only from living cells in nature.

2) Transitory Biotroph     - initially obtains nutrients from living cells, but causes cell death.

3) Necrotroph        - obtains nutrients from dead cells.