Human body contains more nonhuman cells than human?

[Jon_the_Geek]

In late 1992 or early 1993, I read an article in “The Planetary Report” of the Planetary Society about the difficulty of avoiding contamination in probes sent to Mars, and thus the difficulty in varifying that any finding of life on Mars is legit. This article mentioned that there are more nonhuman cells than human cells in the human body (presumably because prokaryotic cells are much, much smaller than eukaryotic cells, so enough bacterial cells could fit in your colon to beat out the cells of your body in number).

I’m looking for confirmation of this factoid, preferably with a cite. Any help would be greatly appreciated. Unfortunately, I don’t have the article in question anymore, and I can’t seem to find it online or otherwise.

[bibliophage]

Welcome to the SDMB, jharmon.

I’ve never heard this one before. The first thing that pops into my mind is that perhaps they were counting mitochondria as “nonhuman cells”. One theory of the origin of mitochondria is that they are descended from distinct organisms that once lived in symbiosis with their host cells.

[Desmostylus]

Can vouch for the accuracy, but here’s the claim:

http://www.madsci.org/posts/archives/dec96/840131722.Dv.r.html

The adult human body contains an estimated 1 * 10^14 cells (a 1 followed by 14 zeros…), 10% of which actually belong to us!! Thus, we have roughly 10 times more cells living in us than we do cells that make up our own bodies. Most of these ‘outside’ cells are bacteria living in the gastrointestinal tract. More than 400 species of microbes live in the colon alone, and can reach a density of 1 * 10^11 organism per milliliter of ‘intestinal lumenal contents.’

[Desmostylus]

Damn. Can’t vouch…

[Jon_the_Geek]

bibliophage–No, it wasn’t counting mitochondria. It wouldn’t be much of a shock that way–since every eukaryotic cell contains multiple mitochondria (or, well, most eukaryotic cells anyway), that’d mean every eukaryote is mostly prokaryote… and that’s just cheating

Oh, and thanks for the welcome. I’m quickly becoming an addict

Darnit, I found another site that claimed 50% of the cells of the human body were human (http://calspace.ucsd.edu/marsnow/library/mars_exploration/robotic_missions/landers/sample_return/planetary_protection1.html). 10-50% seems like a pretty wide range.

It’s mostly too late now–I wanted to include this factoid in a project I was working on about a year ago, but couldn’t find a site that seemed official enough–but I’d like to know…

[Qadgop_the_Mercotan]

Originally posted by jharmon *
** Darnit, I found another site that claimed 50% of the cells of the human body were human. 10-50% seems like a pretty wide range.*

The range is to be expected, depending on how FOS, or “full of Stool” the individual is at the time of the assessment.

[bonzer]

Steve Jones makes a version of this claim in Almost Like A Whale (Doubleday, 1999), at the start of chapter 12:

A newborn baby enters the world and is at once corrupted. At birth, it’s body is sterile, free of the moulds, bacteria and mites that infest the rest of us. From a bacterium’s point of view, the child is a large, fertile and underexploited island. Within moments, it is colonised …
Within a few days, the child contains ten times as many bacteria as it does cells of its own.

Needless to say, he gives no citation.
And this just raises the supplementary question in my mind: is existance in the womb that sterile ?

[Desmostylus]

*Originally posted by bonzer *
**And this just raises the supplementary question in my mind: is existance in the womb that sterile ? **

If the mother has a blood borne infection, the fetus can also be infected. That’s why Rubella and Toxoplasmosis are such problems in pregnant women.

http://www.kcom.edu/faculty/chamberlain/Website/lectures/lecture/congen.htm

The vast majority of infections in pregnant women involve the upper respiratory tract and the gastrointestinal tract. These infections usually resolve spontaneously or resolve after treatment with antimicrobial agents. Such infections remain localized and have no effect on the developing fetus. However, if the infecting organism invades the bloodstream, infection of the fetus may ensue. The most common means of infection of the fetus is via the bloodstream. Less common means of infections include: extension of infection in adjacent tissues and/or organs, or as a result of invasive procedures for diagnosis and therapy of fetal disorders (ex. monitors, sampling fetal blood, intrauterine transfusions).

Results of infection of the embryo and fetus

Infection of the embryo or fetus can result in: death and resorption of the embryo, abortion and stillbirth of the fetus, and live birth of a premature or term infant who may or may not be normal. The effects of in utero infection appear in the live-born infant as low birth weight, developmental abnomalies, congenital disease or none of these. Infections acquired in utero may persist after birth and cause significant abnormalities soon after birth or may not be recognized for months or years.

[Smeghead]

Well, if it helps the math anyway, about 1/3 of feces’ dry weight is made up of bacterial cells. Cite? My medical microbiology class a few years ago.

[Blake]

Close enough Smeghead. Vegetarians and people in developing nations have smaller proportions of bacteria because of the amount of fibre present. It averages out at about 50% for people generally.