150
This review focuses on the development of microbial biofilms, their signaling
and associated drug resistance, and potential emerging strategies to control and disrupt the biofilm.
7.2 Architecture of Biofilm
Biotic as well as abiotic surfaces are susceptible to biofilm formation that progresses
via different stages that may be classified broadly into an adhesion stage, which is
reversible, followed by an irreversible coaggregation/ maturation stage. During progression through different stages of biofilm development, the microbial cells express
or repress genes required for different stages: (i) attachment to a surface, (ii) non
motile growth, (iii) colony formation, and (iv) dispersion. The differentially
expressed unique set of genes enables production of extracellular matrix consisting
of polysaccharides, glycol peptides, lipids, proteins and nucleic acids.
7.2.1 Contacting the Surface: Role of Motility in Adherence
to Surfaces
Hydrodynamic forces and electrostatic forces act as repulsive forces that a bacterium is subjected to in a liquid environment, especially when it is approaching a
surface. In order to overcome these inhibitory forces, bacteria have developed
mechanisms of active motility, which increases its chances of attaching to a surface
(Donlan 2002). Although biofilm development is different for two unicellular lifestyles: motile and non-motile, the generalized biofilm model constructed from the
results of the prior work fits many bacterial species.
Under advantageous conditions for biofilm formation, individual non motile bacteria upsurges its stickiness through increased expression of adhesins on their outer
surface. This stickiness of bacteria advances both cohesive: cell-cell, as well as
adhesive: cell-surface adherence upon encountering a surface (Götz 2002). For
example, certain strains of staphylococcal species express surface proteins including Bap that promote binding to polystyrene surfaces as well as cell-cell interaction
and are part of the extracellular matrix (Lasa and Penadés 2006). On other hand,
when conditions are propitious for biofilm formation, individual motile bacteria
such as E. coli and Salmonella confine to a surface and trigger a striking lifestyle
switch. Bacteria lose its motility by losing its flagella and begin to produce an extracellular matrix that encapsulates and holds the cells together. It was earlier demonstrated using flagella defective or flagella and/or motility minus mutants (fliC, flhD,
motA and motB) that such bacteria are comparatively defective in formation of
biofilms due to lack of initial attachment of cells to the surface (Pratt and Kolter
1998). It is postulated that the motility helps in overcoming the repulsive forces that
are generated between the cells and abiotic surfaces, thus, permitting favorable
B. P. Singh et al.
This review focuses on the development of microbial biofilms, their signaling
and associated drug resistance, and potential emerging strategies to control and disrupt the biofilm.
7.2 Architecture of Biofilm
Biotic as well as abiotic surfaces are susceptible to biofilm formation that progresses
via different stages that may be classified broadly into an adhesion stage, which is
reversible, followed by an irreversible coaggregation/ maturation stage. During progression through different stages of biofilm development, the microbial cells express
or repress genes required for different stages: (i) attachment to a surface, (ii) non
motile growth, (iii) colony formation, and (iv) dispersion. The differentially
expressed unique set of genes enables production of extracellular matrix consisting
of polysaccharides, glycol peptides, lipids, proteins and nucleic acids.
7.2.1 Contacting the Surface: Role of Motility in Adherence
to Surfaces
Hydrodynamic forces and electrostatic forces act as repulsive forces that a bacterium is subjected to in a liquid environment, especially when it is approaching a
surface. In order to overcome these inhibitory forces, bacteria have developed
mechanisms of active motility, which increases its chances of attaching to a surface
(Donlan 2002). Although biofilm development is different for two unicellular lifestyles: motile and non-motile, the generalized biofilm model constructed from the
results of the prior work fits many bacterial species.
Under advantageous conditions for biofilm formation, individual non motile bacteria upsurges its stickiness through increased expression of adhesins on their outer
surface. This stickiness of bacteria advances both cohesive: cell-cell, as well as
adhesive: cell-surface adherence upon encountering a surface (Götz 2002). For
example, certain strains of staphylococcal species express surface proteins including Bap that promote binding to polystyrene surfaces as well as cell-cell interaction
and are part of the extracellular matrix (Lasa and Penadés 2006). On other hand,
when conditions are propitious for biofilm formation, individual motile bacteria
such as E. coli and Salmonella confine to a surface and trigger a striking lifestyle
switch. Bacteria lose its motility by losing its flagella and begin to produce an extracellular matrix that encapsulates and holds the cells together. It was earlier demonstrated using flagella defective or flagella and/or motility minus mutants (fliC, flhD,
motA and motB) that such bacteria are comparatively defective in formation of
biofilms due to lack of initial attachment of cells to the surface (Pratt and Kolter
1998). It is postulated that the motility helps in overcoming the repulsive forces that
are generated between the cells and abiotic surfaces, thus, permitting favorable
B. P. Singh et al.