MadSci Network: Medicine

Re: What makes bacteria grow in your body when you have a infection?

Date: Tue Dec 9 10:30:02 2003
Posted By: Chris Reigstad, Grad student, Molecular Biology and Pharmacology, Washington University in St. Louis
Area of science: Medicine
ID: 1070907390.Me

Good question, Elise!  The short answer to your question is: nutrients derived from your 
body and/or the food you eat, depending on the infection.

Here’s a little longer answer, but it’s an interesting story:
Bacteria need to eat food/nutrients, just like you and me.  Some bacteria have evolved to 
take advantage of humans as a source of nutrients; some can feed on blood cells or other 
types of cells, or even mucus on the surfaces of your skin (like in your nose or your gut).  
Depending on how threatening the bacteria in/on your body are, certain cells of your body 
(‘immune cells’) can be dispersed from reservoirs to where the infection is.  Some of these 
immune cells can kill bacterial cells in an attempt to rid the infection.  However, in some 
cases, if this doesn’t happen or doesn’t work, the bacteria can overwhelm the host (human), 
killing it!  When this occurs, it is usually a result of bad bacteria getting into the 
bloodstream and multiplying like crazy—bad news…

But it may be surprising for you to know that bacteria are growing within us and upon us all 
the time, infection or not!  In fact, it has been estimated that the number of human cells that 
make up an average adult’s body is about 10,000,000,000,000 (10 trillion).  Did you know, 
however, that there may be as many as 100,000,000,000 (100 trillion) bacterial cells in your 
gastrointestinal tract and on your skin at any given moment!  Most of these bacteria have 
evolved to live within the host (human) in a ‘symbiotic’ relationship where bacteria are 
helped grow by the person who eats food (that feeds them both).  Humans are helped by the 
bacteria that break down nutrient molecules, so that they can be absorbed by the intestine 
and used by the cells in your body.

Hope this helps,
Chris Reigstad

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