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Body’s bacteria don’t outnumber human cells so much after all

New calculations suggest roughly equal populations, not 10-to-1 ratio

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5:47pm, January 8, 2016
Enterococcus bacteria

EVEN ODDS  In the human body, bacteria (such as Enterococcus bacteria, shown) were once thought to outnumber human cells by 10-to-1. New calculations show roughly equal numbers of each.

Human bodies don’t contain 10 times as many bacteria as human cells, new calculations suggest.

A “standard man” weighing 70 kilograms has roughly the same number of bacteria and human cells in his body, researchers report online January 6 at bioRxiv.org. This average guy would be composed of about 40 trillion bacteria and 30 trillion human cells, calculate researchers at the Weizmann Institute of Science in Rehovot, Israel, and the Hospital for Sick Children in Toronto. That’s a ratio of 1.3 bacteria to every one human cell.

That estimate could be off by as much as 25 percent, with the average number of bacteria ranging from 30 trillion to 50 trillion. Among individual people, the bacterial count could vary as much as 52 percent, say Ron Sender, Shai Fuchs and Ron Milo. With a fudge factor of 10 trillion to 20 trillion bacteria, the number of microbes may pretty well match the

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