Our immune system, when healthy, is enormously helped by the presence of an army of trillions of friendly bacteria which line the mucus layer of a healthy intestine. In a sense, they are immunity we don't have to work for - they work for us. We just need to provide them with the right environment to keep them happy.
This includes not eating to much food which promotes their yeast adversaries like Candida. These foods include excess sweets, fungus foods like mushrooms, yeasted foods like beer and wine. we also hinder them when we take non steroidal anti-inflammmatories like acetaminophen, ibubrufen and ASA. These drugs thin the mucus layer and make it more difficult for the probiotics to survive.
We can also 'poison' them with chlorine in drinking water or kill them with antibiotics.
Fast probiotic death comes from a course of antibiotics taken without taking extra probiotics. Slow death can come from low level antibiotics from food.
Acidophilus
actually looks like this. This friendly bacteria has many helpful
functions and lives as the dominant species in the small intestine.
Here, it creates an acidic microenvironment next to the absorption
cells, promoting iron absorption. One of the causes of anemia
can be damage to this acid layer as in celiac disease. Many people
are anemic and correcting this lack by taking acidophilus daily
can help promote iron absorption. A good acidophilus can be obtained
here. Click
here for more information.
But when acidophilus is in a healthy condition,
you may observe projections from the tips of the bacteria - acidophilus
buds. These are the beginning of new acidophilus cells which
signifies the health of the bacteria. 
The following drawing shows an illustration of the healthy intestinal villi. These finger-like projections are how we absorb our food. Probiotic bacteria stand on guard to protect us from potential bacterial, viral and yeast invaders. The probiotics are illustrated in green.
The healthy large intestine has another dominant species, Bifido bacterium. This family of bacteria thrive on the soluble fibre in your diet - the type of fibre which comes from many fruits and grains. Bifido bacteria take this fibre and break it down, creating food (butyrate) for the large intestine. Butyrates are fatty acids which help promote healthy peristalsis in the colon and facilitate healthy easy bowel movements. Please click here for more information on a good Bifidus
