We can speak of "microbes" or "micro-organisms," and I used to think that these terms clearly included viruses. And they are used this way by at least some other people; here's a website that refers to viruses as a category of microbe.

However, I recently discovered that these terms are usually defined as referring to microscopic "life," and the definition of "life" with regards to viruses is a contentious topic.

When dealing with disease-causing agents, we can use the word "pathogen." However, not all bacteria and viruses are pathogenic.

All viruses must infect living cells to reproduce, so it is appropriate to refer to all viruses as "infectious agents" (this is what the Wikipedia article on viruses uses in its introduction). However, not all bacteria are necessarily infectious.

The informal terms "bug" and "germ" do exist. While these don't seem strictly limited to pathogens, that seems to be their most typical use. But for a technical audience, does any term exist for which there is a consensus that it refers to both all bacteria and all viruses?

If no single word exists, a short two-word phrase along the lines of "biological entity" would also be OK. (This phrase also comes from the "virus" Wikipedia article, and seems to be the best fit I've found so far. I can also think of a few others along these lines, like "microbial entity" which could be seen as a shorter equivalent to "microscopic biological entity.")

Here are the most important criteria I'll consider when deciding whether to accept an answer:

  • technical correctness: The term must be acceptable regardless of whether one considers viruses to be living or non-living, organisms or not organisms. "Micro-organism" does not meet this criterion because some people do not consider viruses to be organisms.
  • positive scope: It must include all viruses and all bacteria. "Pathogen" does not meet this criterion because not all viruses or bacteria are pathogenic.
  • negative scope: It should not include inorganic objects, whether microscopic or macroscopic. E.g. rock particles. It's OK if it includes protists or multi-cellular organisms, or prions and other "pro-life," or some combination of any of these.

Other important criteria for me:

  • established terminology: I'd prefer a term that is already in use to a neologism. If a neologism seems to be necessary, I'd like it to be linguistically well-formed and etymologically transparent.
  • length: all else equal, I'd prefer a shorter term.
  • grammatical number: I'd prefer a term that can be used in the singular to refer to a single species of viruses or bacteria, as opposed to an always-plural word or a singular mass noun.
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    "Microbe" is a general term that encompasses almost any microscopic organism, including bacteria and archaea. You can't necessarily call a virus, viroid, or prion an "organism", since there's no consensus as to whether such things are even "alive". But for non-specialist use, I think microbe (or microbial life) would probably do. Aug 17, 2015 at 17:13
  • @FumbleFingers: exactly my problem. What am I supposed to call viruses? I just noticed Wikipedia uses the term "biological entities." But if one really defines viruses as "not alive," it seems a bit odd to even call them "biological," since etymologically "biology" is "the study of life." I guess what most people mean when they say that viruses are "not alive" its that they are not living organisms. It's a bit like asking if an organ is "alive"; I would say it is, but that it's not a living organism on its own.
    – herisson
    Aug 17, 2015 at 17:16
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    The usual thinking is that viruses are escaped parts of organisms and are more closely related to their hosts than to any other microbial life form. Since viruses (and other subcell assemblages), archaea, bacteria, most protists, and many fungi, plants, and animals consist of at most one cell, I think calling the whole lot microbes is probly the simplest thing to do. Anything more than one cell can be a parasite if it's dangerous, but monocellular life is what causes "disease" in popular culture. Aug 17, 2015 at 17:22
  • @sumelic: Well, I'd say viruses are obviously "biological". But asking for a specific term covering viruses and bacteria (but excluding all other microscopic life/"proto-life") is a bit like asking for a word that only covers, say, mammals and fungi. (To the professionals, I mean - the average layman would probably be happy with germ for your category.) Aug 17, 2015 at 17:24
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    I don't think the question is a valid one. Viruses and bacteria are so different that I don't see why you should have a blanket term. It seems as though you want a term to cover mammals and trees for example. Aug 17, 2015 at 17:48

2 Answers 2


No single term would cover both viruses and bacteria because there are other biological entities that are similar enough to each, such as prions or protozoa, that would need to be covered by a word that included viruses and bacteria.

The context in which you want to use this term would be useful. For non-technical audiences, you already said that microbe would work because you believed it included viruses. (And I think most non-technical readers would believe the same thing.) Germ might be a better word than you give it credit, for non-technical audiences at least.

Germ is a deceptively simple word that came to us from Latin germen, meaning a sprout, bud, or offshoot. In all of its meanings, the term germ retains the idea of developing into something more mature.

From MedicineNet. Germ as used in the phrase, germ theory of disease, means a small thing that develops into a mature disease.

For technical audiences, I think you accidentally made the best phrase in your question and comments. Something such as sub-multicellular biological entities with basic reproductive capabilities is precise, clear, and unambiguous. A technical reader will understand that this at least includes viruses and bacteria and will likely recognize the other potential members. This phrase could include loose genetic material, too.

You might try moving away from the word biological and towards the word organic. A prion, a virus, and a bacteria are all organic and all have the ability to replicate in the right conditions. Therefore, a phrase such as organic entity with reproductive capacity might work, but it is arguable that a virus does not have the capacity.

  • Thanks; you're right that "germ" fits well in terms of meaning. I guess my only problem is that it often seems to be used pejoratively. The phrases you've used with "reproductive capabilities" and "reproductive capacity" are interesting as well, though a bit long.
    – herisson
    Aug 17, 2015 at 18:04

From what I can tell, microorganism is your best bet.

Microbial population biology is the application of the principles of population biology to microorganisms. ...
Microbial population biology, in practice, is the application of population ecology and population genetics toward understanding the ecology and evolution of bacteria, archaebacteria, microscopic fungi (such as yeasts), additional microscopic eukaryotes (e.g., "protozoa" and algae), and viruses.

I was thinking of offering microbial agent, but microorganism seems to already be used in the way you want to use it. However, it seems you could fall back upon microbial population.

  • Thanks! I'm sure "microorganism" can be used this way. However, my question is a little different: I want a term that even "pedantic" people who define viruses as not being organisms would be happy to use. If you look at the Wikipedia definition of "microorganism," it says "microscopic living organism." There is a fairly visible group of people who deny that viruses are either "living" or "organisms"; I'm wondering what term they would use instead.
    – herisson
    Aug 17, 2015 at 17:37
  • @sumelic what about the other group of pedants who insist that viruses are alive and thus refuse to acknowledge that they are not microorganisms? You'll never please everyone. Aug 17, 2015 at 17:39
  • @Mr.ShinyandNew: I know. I still haven't decided what I personally think about the "should we refer to viruses as living" question. I'm just curious if the people who say "no" have any practical alternative terminology. (If they don't, that would be a fairly strong point against them in my eyes.)
    – herisson
    Aug 17, 2015 at 17:42
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    I feel that your options are to adopt a commonly used term that may be technically imprecise, but most people would understand (even with very little context), or present a new or less used term that may be more technically precise, but most people would understand (perhaps with a little more context). What's important is how hard it is to get people to understand what you are trying to communicate.
    – jxh
    Aug 17, 2015 at 17:44
  • @jhx: that's the most important thing in actual writing. For the purposes of this question, though, the most important condition for me is that the word be technically precise. I want to know if technically precise words for this concept even exist, and if so, what they are. As you can see, I already knew about the word "microorganism."
    – herisson
    Aug 17, 2015 at 17:51

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