My daughter, now ten years old, was given IV antibiotics (gentamicin) on
day 6 of her life in attempt to control projectile vomiting (several
hours later it was discovered that the vomiting was due to a congenital
defect which caused her intestines to twist and kink, a condition known
as malrotation with volvulus, which was corrected surgically).  She
ended up with asthma and allergies to dairy, eggs, peanuts and tree
nuts.  However, there is a family history of asthma and allergies.  It's
interesting to speculate on what caused her allergies, but finding the
cause won't change our daily lives--she has the allergies and we have to
deal with them.  Considering that the hospital was trying to save her
life, I don't blame them for perhaps unintentionally triggering her food
allergies by giving her an antibiotic.  It's my understanding that
probiotics may help prevent diarrhea caused by administration of
antibiotics, but have never heard credible claims that they could
reverse food allergies.