Why does some bacteria help us, and others make us sick?

Different parts of our body are inhabited by different types of bacteria. These live in harmony, and regulate each other’s growth without causing a reaction (infection) in our body.

A reaction (infection) will happen if either:

  • a bacteria native to one part of our body invades another. E.g. Bacteria from the skin entering the blood stream
  • a bacteria is transmitted from an external source into the patient’s body. E.g. Patient to patient transmission of Clostridium Difficile causing severe diarrhea
  • we take an antibiotic that suppresses the growth of one native bacteria, and disrupts the balance. E.g. Vaginal thrush caused by overgrowth of candida albicans (fungus)