Normal flora can become pathogenic if it finds a way to a part of your body in which it doesn’t normally reside. For example, E. coli is NOT pathogenic when it’s in your lower intestines; different story when it finds a way into your bladder. …and even within the normal ‘home’ of a microbe in question, if your internal chemistry or immune system get out of whack, sometimes that resident flora can get out of control. This is basically ‘opportunistic pathogens’ in a nutshell.

So… every square.