Infants whose gut is colonized by ES. coli bacteria early in life have a higher number of memory B cells in their blood. according to an article posted in the May of 2012 issue of the Journal of Immunology. There has been a trend caused by an increasingly hygienic lifestyle where this colonization is occuring later than in previous decades. This is believed to be associated with immune deficiencies that have lead to an epidemic of allergies and possibly other autoimmune disorders. Healthy newborns should not be over-protected against natural exposure of the gut flora.