Fig. 3 also shows that higher nutrient levels resulted in higher
maximum OD values of adhesion in both tested strains. Higher
nutrient levels are known to yield higher bacterial cell counts in
suspension. This could not only give cells more chances to interact
with other cells and with the surface; but could also lead to a more
rapid depletion of nutrients in solution, higher production of acid
and stronger competition among cells. These stresses were prolonged
and could affect quorum sensing of cells in the positive way
to form biofilms. Nutrient starvation has been demonstrated to
increase the expression of agfD promoters relating to biofilm
formation of S. typhimurium. The depletion of nitrogen and phosphate
compounds gave signals to switch on agfD promoters in S.
typhimurium (Gerstel & Romling, 2001).