When testing water systems, we test several ports for Aerobic and Y&M Counts. Lately the Y&M plate for a port that comes after a carbon media bed has been turning up with high counts. We use m-Green y&f broth from Neogen. Also, the aerobic count for the same port is very low. The colonies that appear on the yeast and mold plate are crateriform, beige, and matte. It is unclear if they are yeast or bacteria at this time. My questions are as follows:
1) Are there circumstances which would allow for growth of bacteria on my y&m plate?
2) What conditions would arise in which I would have a high yeast or bacterial count but a low total aerobic count?