25 Mar 2016

Truth, the Internet, and the Number of Bacteria on Your Body

True Stuff cartoon Now Magazine Jan Thornhill

Before I started writing and illustrating kids' books, I did a weekly cartoon for Toronto's Now Magazine. I mined what I thought were entertaining factoids out of whatever I was reading or whoever I was listening to at the time, and illustrated these "truths" in scratchboard. I even called it, for a while, "True Stuff." 

Truth be told, I sometimes accepted as truth anecdotes told to me by other people, or things that came from dodgy sources such as supermarket tabloids. I admit, too, that I sometimes even made up some of what I drew. The above cartoon, however, was supposed to be one of the honest-to-gosh fact-based truths I'd come across and copied into my notebook. Perhaps you've heard or read something similar, something like "bacteria in the human body outnumber the body's own cells by 10:1."

child's microbe hand print
Tasha Sturm, a college microbiology tech, got her young son to gently
press his hand on a petri dish full of agar after he had been outside.
This is the fabulous collection of bacteria that grew! (photo: Tasha Sturm)

When I first came across this "teacupful" tidbit back in 1985, without the luxury of having everything at my internet-connected fingertips like I do today (even in the woods, even in the middle of the night, even a hundred miles from the closest big city), my fact-finding abilities were heavily reliant on what I read in books, newspapers, and magazines. Back then, I had to trust what I read, mostly because it was so very difficult to question the veracity of the printed word. How, back then, if I had questioned the trustworthiness my source, would I have been able to verify if it was true? I mean, even if something like the above statement about "a teacupful" of bacteria was sourced from, say, a research paper in an obscure journal, how would I, a non-academic, have been able to access such a thing back then? 

child's handprint bacteria
A close-up of the large flower-shaped colony from the above photo
that is probably made up of several million bacteria (Tasha Sturm)

My point is that back then, in the olden days before the internet, I had an excuse to repeat things that were sometimes untrue. Or at least more of an excuse than I have now. (I also seemed to have a heck of a lot more spare time back then, precisely because I didn't have easy access to so many of the scientific papers I now read—but that's a different story.) 

Back to the number of microbes on and inside a human body. I would never have fished out this old cartoon if I hadn't recently come across the following headline (on the internet, of course!): "Scientists bust myth that our bodies have more bacteria than human cells."

cut paper sculpture microbe Rogan Brown
Artist Rogan Brown's amazingly beautiful (and intricate!)
hand-cut paper sculpture of a bacterium  (Rogan Brown)

Here's the gist of what's come to light. This 10:1 bacteria-to-human-cell statistic, which gets almost nine thousand pre-2016 hits on Google, is based on a statement published in a review in 1977, a statement which had, in turn, been based on an earlier unsubstantiated calculation taken from a 1972 article. A group of researchers in Israel and Canada now say the ratio is more likely to be, on average, closer to one-to-one. Some people might have double that number of bacteria, some only half. And everyone loses almost their entire microbial load on a daily basis—at least they do if they're "regular," since the vast majority of human's bacteria reside in the colon. So the ten-to-one ratio is actually an academic urban legend.

But there's the rub: I haven't actually read the new study, nor have I read either the journal article or the review from the 1970s that I've cited in this post. Am I lazy, or is it reasonable for me to trust the distilled versions of the paper that have been published on the websites of the journal Nature, the National Geographic, and Scientific American, among others? I can't answer that. All I know is that it's getting harder and harder to figure out what is believable, not just on the internet, but also in contemporary books since so many are now based on internet research. I just hope I rehashed the gist of what I've been reading about the current research without garbling it too much—because I'm obviously as capable as anyone else of modifying what I've read when I rehash it.

Elin Thomas petri dish mold and bacteria art
Artist Elin Thomas uses felt and crochet to create petri
dishes packed with "moulds" and "bacteria." (Elin Thomas)

Take that original teacupful of bacteria "fact" I riffed off of all those years ago. Even with the mighty internet I cannot find a specific reference anywhere to "a teacupful" of bacteria on the human body. What I have found, though, are two separate references to the mass of all those trillions of bacteria found in humans equalling that of "a teacup Yorkie" or as being "roughly the same weight as a teacup chihuahua." Perhaps I was guilty way back then of dropping a qualifier in my copying down of this cool little factoid! 

More Academic Urban Legends:

If you think spinach is a rich source of iron, read this entertaining paper: 

Check out our very own Helaine Becker's UBC article that highlights an academic urban legend about how pearls are formedAnd if you happen to meet Helaine, ask her about Mendel's Peas.

More Information:

Directions for making a bacteria handprint in agar are contained in the Comments section of Tasha Sturm's original post on Microbeworld.org (N.B. Once the plates are grown they should NEVER be opened!!!!! The colonies on the plate can represent millions of bacteria that could potentially make someone sick. Mold also contains spores that could be inhaled causing serious problems as well.)

Rogan Brown's website with more dazzling cut-paper microbe art
Rogan discusses his science-based art in a short video

More of Elin Thomas's work on Flickr and on Etsy 

And if you want to know all about microbes and the human body, pre-order Inside Your Insides: A Guide to the Microbes That Call You Home, the latest book written by Sci/Why's own Claire Eamer (illustrated by Marie-Eve Tremblay)!

Inside your insides cover Claire Eamer


Ron Sender, Shai Fuchs, Ron Milo. Are We Really Vastly Outnumbered? Revisiting the Ratio of Bacterial to Host Cells in HumansCell, 2016; 164 (3): 337

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