Although we usually think of bacteria as being dangerous and a cause of human diseases, the truth is that bacteria can also be good, depending on the species and location. Certain types of bacteria actually play a vital role in the ecosystem--both inside our bodies and externally, in the environment around us.
Bacteria Are Part of Your Innate Immune System
Some species of bacteria do make you sick, but others may actually prevent you from getting sick. Your skin and mucus membranes have what doctors call a "normal flora," meaning a population of resident bacteria that live on these surfaces on a permanent basis. The bacteria in your normal flora are harmless, and most of the time you don't even know that these bacteria are there. But when your body encounters potentially pathogenic bacteria or a parasite, the normal flora can prevent these dangerous bacteria from being able to take hold. They do this either by simply crowding out the invaders or by producing substances that kill the potential disease-causing bacteria. Thus, these "good" bacteria can protect you from "bad" bacteria that might otherwise make you sick.
Bacteria Help You Digest Food and Produce Vitamins
Your intestines are lined with a normal flora of bacteria. These bacteria, sometimes called the "gut flora," can prevent infections by gastrointestinal pathogens as outlined above, but the normal flora in the gut can also help by breaking down food that can't be digested by your body's own enzyme production. This frees additional nutrients for absorption that would otherwise have been lost to waste.
In addition to helping break down food, the bacteria in your gut flora produce small amounts of B vitamins, supplementing what you get naturally from food. Intestinal bacteria are also your body's primary source of vitamin K, which plays a key role in blood clotting. This is the reason why newborn babies routinely need a shot of vitamin K; babies lack gut flora at birth.
Bacteria Maintain the Natural Cycle of Life
When plants and animals die, such as when trees fall in the forest, it is bacteria along with fungi that break down the remains and return nutrients to the soil. This replenishes the soil's ability to nourish new plant growth. Without the action of bacteria, soil would cease to be able to nourish plant growth and dead organisms would not be broken down, constituting a serious disruption to the natural cycle of the ecosystem.
Bacteria Are Used in Food Production
Many food production processes involve bacteria. Fermentation of milk into cheese and yogurt, for example, would not be possible without the activity of bacteria found in lactic acid. These bacteria are also sometimes used in making wine, in sausages and deli meats, and in the pickling of vegetables.
Bacteria Have Industrial Functions
Some species of bacteria can be useful in agriculture and other large industries. For example, oil-eating bacteria are used to help clean up oil spills, and some types of bacteria can help degrade pesticide residues on farms.