@annagh If the PMN's are on the slide examined under the microscope, they are considered "normal flora." PNM's are a specific type of white blood cells that fight infections, and do not grow in a culture. If you have an active infection, that, not PAM'S, will grow in the culture, alerting the doctor that you may need treatment.
Many people are "colonized" by a specific bacteria that isn't an acute infection, and doctors usually choose to allow the body to fight it instead of using antibiotics. For example, I have staph ( not MRSA) that appears every time I get any small wound. We only treat it when it happens, but my WBC (PNM is only one kind) is always elevated.