I too work in the NICU and have posted this same question. We currently do not
routinely test breastmilk. This has become an issue for us as a mom with
triplets  had a mastitis. For some reason her milk was cultured and grew out
Group b strep. We were unable to use her milk. After research on Lactnet and
through text info as well as help from Marsha Walker we found that we could
heat treat the milk. Unfortunately one of the babies became extremely ill and
mom decided she had had enough. They have tolerated the formula well, probably
because they at least got a few weeks of the milk. Anyway, the neonatologists
are questioning routine culturing vs. checking those moms with mastitis. We
are trying to find documentation against this. Dr. Jack's response was to also
routinely culture and check the formula. Also check the standards of the Human
Milk Banking Association of North America. If you check the archives you'll
also find other articles for reference given to me by Dr. Jack(can't put my
hand on them now). Good luck and let me know what info you find out as we're
in the same position.
Lisa Enger RN BSN IBCLC