Incubation time
The effect of the incubation time on the adhesion of
probiotics has not been fully investigated. In most assays
probiotics are incubated for 1/2 h with the substratum.
Some investigators have reported little or no effect of
incubation time on the level of adhesion of propionic acid
bacteria (72) and bifidobacteria (47). However, incubation
time may have a major influence on the observed adhesion
(Fig. 2). This phenomenon can be explained by sedimentation
of the microbes. As incubation progresses, more and
more microbes sediment and increase their local concentration
on the substratum. This allows more bacteria to bind
than in a homogeneous suspension and leads to artificially
increased levels of adhesion. Since sedimentation is not
likely to happen in vivo, it should also be avoided in
adhesion assays. This can be done by gently rocking the
substratum to counteract sedimentation, which would also
mimic the intestinal flux, or by using standardized incubation
times. The incubation time should be based on a
physiologically relevant contact time between probiotics
and the intestinal mucosa, this being different in different
parts of the intestine and possibly ranging from 10/15 min
in the upper small intestine to /1 h in the colon.