We do not do any routine culturing of BM before it is given to premies.  Our
Moms get the standard instructions re cleaning: hot soapy water after each
use, and boil once a day.  We use sterile volufeeders (once only) to collect
milk for our tniest, sickest kids, but when they move to our "grower" unit,
Mom's reuse the collection bottles after hot soap and water or diswasher
cleaning.
Are all three babies sick with the SAME organism?
Is each baby sick with an organism found in her/his mother's milk?
It may be just a coincidence - depends on what percentage of infants in your
unit are getting breastmilk.
Although breastmilk is not sterile, if we DO culture BM for some reason, we do
not use it if it contains > 10,000 col/ml of skin flora or any gram negatives,
or pathogens.
I would not use BM with GBBS in it.
Nancy Wight MD, FAAP, IBCLC
Neonatologist
San Diego CA