Each of us, as an adult, has around 30,000,000,000,000 viable microbes living in our intestines and body, comprising over 400 different species. How much do all these bugs weigh in an average adult? Around 200g, according to the US Library of Medicine. However, this estimate varies widely. They help to digest food, especially vegetable matter and keep harmful bacteria (or pathogens) at bay.
Examples of helpful microbes include Lactobacillus bacteria that make up parts of the normal human oral and gut flora. They are able to ferment lactose to lactic acid. This makes them important as a preservative and in yogurt production. If you add lactic acid bacteria to thin strips of a cabbage, they ferment the vegetable to create sauerkraut.
Humans cannot digest many plant molecules on their own. Bacteroides thetaiotamicron helps humans by digesting plant molecules for us to digest. We also use the nitrogen fixing abilities of Rhizobium to help with crops and other plants’ growth.
Bacteria live all over our body, helping us to digest and to keep our skin healthy.
So not all bacteria are bad of us, just a few.