Put in a simple modification-related context, bacteria are tiny organisms which cause infection and disease and in very rare cases have been documented as the cause of death after even a simple modification (for example, MVP issues or mastitis).
Bacteria are found almost everywhere on Earth. A teaspoon of soil may contain several hundred billion bacteria, and even thoroughly washed hands contain several million bacteria in every square inch of skin.
Wound infections can occur when bacteria not normally present in an area are introduced into that area. An example of this would be if a piercer did not disinfect his or her hands after going to the toilet and before piercing a client. In this case, bacteria (such as E. coli) from the piercer's digestive tract could be transferred from the piercer's feces to the piercer's hands, which could then be introduced to the fresh piercing, if the piercer had not put on his or her gloves properly or simply failed to use gloves at all.
Wound infections may also occur when a very large number of normally present bacteria are introduced into a piercing, such as Staphylococcus aureus, the bacterium which commonly causes spots and boils on the skin. This commonly happens when a person with a fresh piercing touches his or her skin and then touches the fresh piercing, which may then become infected.