Normal Flora

The normal flora are bacteria which are found in or on our bodies on a semi-permanent basis without causing disease. There are more bacteria living in or on our bodies, than we have cells of our own. A human body contains around 1013 cells. The human body is home to around 1014 bacteria. One fourth of fecal weight is made of bacteria!

The normal flora are particularly important in the large intestine.

Normal flora are also found in the

The normal flora protect us from disease by

1. Competing with invaders for space and nutrients

2. Producing compounds (bacteriocins) which kill other bacteria

3. Lowering the pH so that other bacteria can't grow

In addition to the above ways of protecting us from disease our normal flora help us in other ways. Of course, there is a down side as well...

The Good Side

The Bad Side

Produce vitamins we are unable to produce such as vitamin B12.

If the normal flora escape from their normal location, they can cause disease. For example, Escherichia coli, commonly found in the intestine, can cause urinary tract infections if introduced into the bladder.

Boost our immune system — Germ free animals (born and raised in a germ free plastic tent) are very susceptible to disease when removed from the germ free environment because their immune system is underdeveloped.

Help digest food

Immunosuppression can allow otherwise harmless bacteria to cause disease. AIDS, some cancer treatments and transplant rejection drugs all suppress the immune system and allow the normal flora to cause occasionally serious disease.

If you were trying to invade an area filled with normal flora:

How would you find a space to live? and food? if all was taken up by the normal flora
How would you avoid being killed by bacteriocins?
How would you survive the low pH?

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