Fecal samples have been used in most colonization studies with
probiotic bacteria. These, however, reflect only the bacteriologic
situation in the fecal material and do not give an accurate picture
of the different parts of the gastrointestinal tract or the mucosal
layer of the gut. The use of biopsies from the intestinal mucosa is
a more accurate means of determining colonization. Lactobacillus
strains were found to adhere to rectal mucosa obtained from volunteers
who had consumed a fermented oatmeal soup (7).
When tested in vitro, probiotics are usually grown in laboratory
media. With many probiotics, the aim is at least transient
colonization, in which case the probiotics may need to grow or
at least metabolize in the intestine. The adhesive properties,
metabolism, and morphology of probiotics grown in intestinal
contents or intestinal mucus have been shown to be different
from those of probiotics grown in laboratory media. These differences
may affect the health effects of the probiotics. By using
culture media more resembling the nutrients available in the
intestine, one may obtain a more accurate understanding of the
properties of probiotics in vivo.