organism
Meaning of organism: A biology word that shrinks in the clinic, where the organism almost always means whatever has grown in the culture bottle.
Definition of organism
An organism is any individual living thing, from a single bacterial cell to a whale. It is bounded, uses energy, responds to its surroundings and can reproduce. In clinical speech the word is often narrowed to mean the microbe causing an infection, so a note saying the organism was identified refers to a bacterium or fungus, not to the patient.
What counts as one?
Living things are sorted into broad groups, and organisms from most of them turn up in medicine. Bacteria and archaea are single cells that keep their DNA loose rather than in a nucleus. Everything else, from a fungus to a human, packages DNA inside a nucleus. Fungi form a kingdom of their own and are not plants, a point often muddled because they do not move; they feed by absorbing material from their surroundings rather than making food from sunlight. Parasite is not a biological group at all but a way of living, and it covers both single cells and worms.
Are viruses organisms?
Usually not, under the standard definitions. A virus has genetic material and a protein coat but no machinery to build proteins or generate energy, and it cannot copy itself without hijacking a cell. It is therefore called an infectious agent rather than an organism, which is why a laboratory report on RSV speaks of detecting a virus rather than growing one. The boundary is a matter of definition rather than a discovery waiting to be made, and some biologists dispute it.
Why does the word narrow in a hospital?
| Phrase | What is meant |
|---|---|
| The organism was isolated | A microbe grew in culture and was identified |
| No organisms seen | Nothing visible on the stained slide |
| Causative organism | The specific microbe held responsible |
| Whole organism | An entire living animal, as in an animal model |
Context does the separating, and the broad biological sense of the word survives mainly in research writing and in teaching.
Also known as
Used in a sentence
Blood cultures were taken before antibiotics to identify the causative organism.
Good to know
Viruses are conventionally excluded from the term because they cannot build proteins or reproduce without a host cell, so a report naming an organism generally means a bacterium, fungus or parasite.
Word origin
Where “organism” comes from
Organism derives from the Greek organon, meaning instrument or tool, by way of the Latin organum, carrying the sense of a body made of working parts.