MadSci Network: Microbiology

Re: Why are bacteria affected by pH and temperature?

Date: Wed Nov 11 17:21:10 1998
Posted By: David Beck, MadSci Admin
Area of science: Microbiology
ID: 910639714.Mi


Do bacteria like acidic environments?
Yes some LOVE it, No some HATE it!

Do bacteria in the gut like acidic environments?
Yes some LOVE it, No some HATE it!
The way the gut works. We start in the mouth and chew are food and add saliva to it. The saliva has enzymes that attack the bacteria. Some bacteria are very sensitive to these enzymes and are killed, but many bacteria are "tolerant". That means the don't like the enzymes but that they don't dislike them either.

Now the bacteria, food and saliva proceed to the stomach. Here there are more enzymes, and more importantly a VERY acidic environment. There are many bacteria that are rapidly killed by the acids, but some are what is called acid tolerant. This organisms don't like the acidic environment and just sort of hang out till the make it out of the stomach. There are also a few bacteria that LIKE the acidic environment. These acidophiles (acid lovers) grow in the stomach, and colonize it (ie the find ways to stick to the stomach). The acid tolerant bacteria, acidophiles that don't stick, and the odd non-acid tolerant bacteria that somehow survives, and the food leave the stomach and enter the small intestine.

The small intestine is like a water slide. Things move REALLY fast. Pancreatic juices are added to the food and bacteria mix. The pancreatic juices neutralize the acidic mixture coming from the stomach. But remember the bacteria are on a water slide. Most bacteria don't stay in the small intestine. Some bacteria are able to swim or have ways to stick to the small intestine, and thus they stay in the small intestine, but most bacteria don't stay. Farther down the small intestine, things start to slow down. More bacteria find a home. As you get to the large intestine the bacteria have started to use up the last of the oxygen. Many bacteria require oxygen to grow, and so they don't grow in the large intestine. But bacteria have different oxygen requirements, there are three main groups:

  1. Obligate Aerobe : REQUIRES oxygen to grow
  2. Facultative Anaerobe: LOVES oxygen to grow, but when it runs out of oxygen it will use other things to keep growing.
  3. Obligate Anaerobe: HATES oxygen. Survives poorly in in oxygen rich environment but grows well in the abscence of oxygen.
So as you can see Obligate Aerobes won't grow once the oxygen is used up in the intestine. The facultative Anaerobes will grow in both places, and the obligate anaerobes, that weren't growing before will now start growing. So in the large intestine you will find alot of obligate anaerobes growing.

So briefly you bring bacteria into your mouth, those that tolerate the saliva will stay there, and grow on your teeth. Most will go to your stomach. In the stomach most bacteria will be killed, some who are acid tolerant will survive, but a very few who are not acid tolerant manage to sneak through, and a very few bacteria that are acidophiles will grow in the stomach.

Then in the small intestine those that can swim are more likely to stay, but most move to the end of teh small intestine and the large intestine. Here the bacteria grow and quickly use up the oxygen. Then some bacteria STOP growing, some keep growing, and others START growing.

Hope that helps.

Best Wishes,
David Beck
Madsci Admin

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