There are no universally agreed normal/acceptable levels for bacteria or yeast and mold in a home. However, you may find levels suggested by various organisations. I would say that since there will always be bacteria/mold/yeast in houses, any levels that appears abnormally high is unacceptable. However, apart from the levels, you have also to consider what organisms are present since some are more harmful (that is can cause diseases) or destructive than others. Hope this helps.