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Chapter 1
[82]. Previous research has suggested that cellulose plays a crucial role in
biofilm formation including in batch biofilm reactor systems [82], epithelial
cell surfaces [83], glass cover slips [84] and alfalfa sprouts [85]. However
others have suggested that cellulose is not crucial for Salmonella biofilm
formation on gallstones [84] and polystyrene [86]. The activation of
cellulose production comes as a result of the regulator AdrA. AdrA
stimulates cellulose formation via the bacterial cellulose synthesis operons
bcsABXC-bcsEFG [82]. Römling hypothesised that the production of
cellulose is subject to selective pressure and under certain conditions it is
not produced in host-invasive diseases (in less common serovars). Römling
et al. suggested that as cellulose is not always found in strains isolated
from invasive diseases, this may indicate that selective pressure may
prevent the production of cellulose under certain invasive conditions.
Römling et al. also suggests that the production of cellulose by strains such
as S. Enteritidis and S. Typhimurium outside of an animal host may allow
the bacteria to survive in other environments [87]. The hypothesis that
cellulose is not necessary for virulence has been supported through in vivo
studies elsewhere [82].
Curli and cellulose combined form the extracellular polymeric substances
(EPS) or matrix of a developed biofilm [78]. It is suggested that curli provide
the thin rigid link between cells whereas cellulose provides more stable
attachment through elastic polysaccharide bonds [87]. Gualdi et al.
suggested that csgD over expression results in limited production of curli,
while deletion of the bcsA, gene responsible for cellulose production
resulted in increase of curli-dependent bacterial attachment [88]. Gualdi et
al. also suggested that both expression of curli and cellulose may be
interchanged depending on the requirements of the cell and the host
environment [88].
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