If you pasteurize it correctly then it will kill all the unwanted stuff and leave you with healthy soil.

' Using pasteurized soil is another way gardeners avoid
diseases. Fill a pan or metal tray with a 4 inch, or less,
layer of moist soil. Bury a one and a half inch diameter
potato in the center of the soil, then cover the pan with
aluminum foil, and seal the edges. Punch a small hole in
the center of the aluminum foil and insert the bulb end of a
candy thermometer. Place the pan in an oven at 180 to 200
degrees. After the thermometer reads 180 degrees, leave the
soil in the oven 30 minutes then remove and allow it to
cool. The potato will be cooked if the soil is properly
pasteurized. Pasteurizing the soil is useless if dirty
containers are used. Pasteurizing soil in the oven can
create an odor some people find offensive. Clean clay pots
can be sterilized by baking while the soil is heated. Pots
can be sterilized by soaking them in a solution of one part
chlorine bleach and nine parts water. Rinse, and allow the
pots to dry thoroughly before filling them with soil. '

Here is a link that might be useful: http://www.cyber-north.com/gardening/seed.html