Flora and fauna of the gastrointestinal tract

I’ve just learnt the ‘fact’ that the amount of bacteria cells in our gut outnumbers the number of human cells in the rest of the body by a factor of 10.

I heard this on a well respected radio science program, so my initial reaction of ‘Cite…’ has been called into question.

The relative size and therefore mass of the cells in question appear to confirm this hypothesis but I can find no ‘Proof’.

Over to you guys…

The wiki entry on Gut flora - http://en.wikipedia.org/wiki/Intestinal_flora has 4 cites for the 10x claim. I haven’t checked them out, but the references look good. Oh, and the 10x is just for the intestines. It’s not counting mouth and skin bacteria.

^ a b c d e Björkstén B, Sepp E, Julge K, Voor T, Mikelsaar M (October 2001). “Allergy development and the intestinal microflora during the first year of life”. J. Allergy Clin. Immunol. 108 (4): 516–20. doi:10.1067/mai.2001.118130. PMID 11590374. http://linkinghub.elsevier.com/retrieve/pii/S0091-6749(01)96140-8.

^ a b c d e f g h i j k l m n o p q r s t u v w x y z Guarner F, Malagelada JR (February 2003). “Gut flora in health and disease”. **Lancet **361 (9356): 512–9. doi:10.1016/S0140-6736(03)12489-0. PMID 12583961.

^ a b c d e f g h i j k l m n o Sears CL (October 2005). “A dynamic partnership: celebrating our gut flora”. Anaerobe 11 (5): 247–51. doi:10.1016/j.anaerobe.2005.05.001. PMID 16701579. http://linkinghub.elsevier.com/retrieve/pii/S1075-9964(05)00068-5.

^ a b c d e f g Steinhoff U (June 2005). “Who controls the crowd? New findings and old questions about the intestinal microflora”. Immunol. Lett. 99 (1): 12–6. doi:10.1016/j.imlet.2004.12.013. PMID 15894105. http://linkinghub.elsevier.com/retrieve/pii/S0165-2478(05)00005-2.

Remember that an eukaryotic cell (with nucleus, mitochondria, ribosomes, etc., and found in plants, animals, protozoa, Algae, and fungi) is enormous compared to a prokaryotic cell (bacteria and cyanophytes). In fact, the prokaryotic cell is approximately the size of one of the organelles within the eukaryotic cell, which may actually have originally been free-living prokaryotes themselves.

To help emphasize Polycarp’s point:

This is a picture of an epithelial (skin) cell covered in bacteria. Bacteria are generally much smaller than any of our cells, and it’s easy to see how we’re outnumbered.

Also, there’s the following fact that I seem to be bringing up with disturbing regularity here lately:

Your poop is about 1/3 bacteria by dry weight.

I’ve heard these bacteria are necessary for digesting food. So where to they come from?

Exposure to environmental bacteria after birth. Our first exposure is during delivery and then being handled by parents and other caregivers. Different bacteria are encouraged depending on whether the baby is fed breast milk or cow/soy formula. After that, simply exposure to our “contaminated” world.

Good one!

Thanks to Polycarp and to Antigen for the picture. My first reaction was “that can’t be right!”

In a vaginal birth, the inoculation starts in the birth canal. So a C-section baby takes a bit longer. But the world eventually enters.

Apparently, people do differ quite a bit in their bacterial mix in the gut and this is now thought to (maybe) have implications for health, including how easy you gain weight.

I have read that your poop (and mine) is about 1/4 E. coli. I wonder what the remaining 1/12 is.

So I take probiotic supplement. I find that they really do work. But my question is: why do I have to take them every day? Why aren’t the bacteria I’m ingesting multiplying enough in my stomach to a point where I don’t need to help them along?

E coli is not the only intestinal bacteria. There’s lots of other kinds, although I can’t remember the number I once heard. A few hundred different kinds, I think.

Are the probiotics targeted to the stomach? I’d assume that was a less hospitable environment, what with the shomach acid and all. I’d assume they are targeted to the intestines, where all the cool crowd hang out.

There could be two reasons to take them every day. One is that they’re not as hardy and/or as suited to the environment at the natural gut flora are. They keep getting out-competed. The other is that no one gets money for pills you don’t take.

Well for one the jury is still out about the efficacy of probiotics. Sure there have been a few studies that demonstrate some potential benefits for GI function (though the studies may have been privately funded). However, I do know of one study that could not detect any of the probiotic strains in the, ahem, human effluent after ingestion of the probiotics (woo! lab techs digging through your poop!). Who knows why they might not take hold in your gut?

Just for fun, I’ll add a reminder that human cells vary widely in their size, a single neuron cell can run from the toe to the spine. I don’t know what the mass difference is between a single bacteria cell, and a 3’ long neuron, but I’m betting it’s greater than 10x.

I should have said “digestive system” and not stomach. That is what I meant and was being dumb for a second.

I have reflux. When I take a certain brand of probiotics the 3 times daily, my heartburn and reflux incidents are less frequent and less severe. If I take a different brand, the effects aren’t as good. I didn’t take any for a while around Christmas and I ended up having some of my worst attacks ever. I started back up again recently and haven’t had an attack since and have cut down on my OTC reflux meds.

It could totally be placebo effect. That’s kind of what I was thinking because I couldn’t figure out why they weren’t multiplying on their own. Being out-competed is a good answer, assuming it’s not all just in my head.