confused on terminology used in microbiology - cells = colonies = CFU's ? (Sep/23/2009 )

To my knowledge there is is a difference between cells and colonies or am I wrong here?

I was reading a paper and the author was talking about how his system was much better then another author because his detection limit was far better.
He could detect less colonies then the other author.
However when reading the paper of that other author I noticed that he never spoke about how many colonies he detected as a minimum because he refered to the number of cells he detected!
This seems a bit strange to me and makes the whole equation made by the author wrong or am I so wrong here?

And what with CFU's ? If you count the CFU's, then you do count colonies ? I mean: colonies counted is the same as CFU's counted? Or is there a difference between this too?

I noticed that there seems to be a lot of problems about the use of those words, mistakes made because of languages problems I think.

What are your opinions on this?

Suppose to some extent it depends on the technique and context. If counting with a hemocytometer, it could be cells whereas with plate counts would be cfu. In nature you'll prob not see so many isolated, single cells and I recall an article in the old ASM News (now Microbe) arguing that we should always speak of colonies.

Can you give us the citation?

you can find the articles at the following links:

article one: using cells, not colonies
(Development of a PCR-based method for the detection of Listonella anguillarum in fish tissues and blood samples)


article that is refering to the other article and using colonies in stead of cells.
(Species-speci¢c PCRdetection of the fish pathogen, Vibrio anguillarum , usingtheamiB gene,which encodes N -acetylmuramoyl-L-alanine amidase)

1st article is technically correct as it cites an unreported experiment that claimed calibration of specific individual viable counts to a McFarland standard. Authors presumed individual cells and maybe they actualy obsrved them as such.

The 2nd reports the measure as the concentration. The same as if the 1st paper reported senstivity in terms of a fraction of a McFarland standard. To my perspective - it's incorrect but that's subjective. Note they proposed to count "cells" but reported "colonies."
"Viable cells were determined by cell counting from the internal organs of the fish after injection."


It may also be a product of translation. If there's a problem - it's clearly with the reviewer and editor of the journal. Write the editor and ask him/her.

If each colony arose from a single cell, then the number of cells plated equals the number of colonies and equals the number of colony forming units. But we can't know that a single colony arose from a single cell -- perhaps when spreading the plates, two or more cells wound up on top of one another. The colony that arose from this pair (or more) of cells could be indistinguishable from a colony that arose from a single cell, thus the term "colony forming units" was coined.

In practice, it's usually not such a big deal, unless you're working with cells that aggregate extensively. Also, mathematically it's usually not so big a deal, because -- if done correctly -- you report cfu's per ml after averaging several replicate experiments or reporting the most probable number or other such manipulations, so the rare event does not invalidate the results anyway.

GeorgeWolff on Sep 23 2009, 11:50 AM said:

why colonies....I think the term CFUs is much more appropriate.....like homebrew pointed out already???

eum thanks for the replies, they kinda state what I was thinking.

anyway the second author was wrong with his comperisation when he spoke of colonies in stead of cells since he could not know that each colony was from one cell.
Or indeed, maybe its an error in translation.

Each viable cell forms a Colony Forming unit (CFU) when cultured on a plate.

baccilus on Wed Aug 25 07:12:22 2010 said:

This is incorrect. Were it true, then CFU's would always equal viable cells, and there would be no need for the term. As pointed out above, two or more viable cells might land on the plate in such close proximity that the colony formed by their growth is indistinguishable from a colony that arose from a single viable cell. In such a case, the number of viable cells plated is actually larger than the number of colonies arising on the plate. Since there is no way to know whether any given colony on the plate arose from a single cell or from multiple cells in close proximity, the term CFU is used.

You can think of CFU's as the *minimum* number of viable cells plated, because there must have been at least one viable cell in that location to produce the colony seen, but since there might also have been more than one cell there, CFU's does not automatically equal the absolute number of viable cells plated. The number of CFU's can be equal to or less than the number of viable cells plated, but it can never be higher than the actual number of viable cells plated.