152
7.2.3 Fimbriae Affect the Irreversible Adhesion to Surfaces
In case of biotic surfaces, bacterial attachment to the host surface is mediated via the
specific recognition of bacterial surface proteins by the extracellular proteins or
carbohydrate moieties expressed on surface of the cells/ tissues. In E. coli, three
categories of fimbriae strengthen the bacteria-to-surface interactions; type 1 fimbriae, curli, and conjugative pili. Type 1 fimbriae (or pili) are filamentous adhesins
produced by both commensal and pathogenic E. coli isolates. Type 1 pili can adhere
to wide range of eukaryotic surface receptors in mannose dependent manner. Type
1 pili tip adhesin, Fim H, binds to eukaryotic mannose oligosaccharides and is
involved in pathogenesis caused by uropathogenic E. coli. Moreover, curli fimbriae,
also called thin aggregative fimbriae, were initially identified in E. coli, are also
produced by other Enterobacteriaceae such as Shigella, Citrobacter, and
Enterobacter. Curli bind to eukaryotic proteins such as fibronectin, laminin and
plasminogens, to promote adhesion to eukaryotic host. Curli production is encoded
by two sets of divergently transcribed operons: csgBA (structural components of
curli fimbriea) and csgDEFG (regulatory and export machinary of curli) (Ben Nasr
et al. 1996). Researchers showed that F conjugative pilus could functionally substitute for Ag43, curli or type 1 fimbriea. In Pseudomonas aeruginosa, attachment and
movement through the viscous cell surface is aided by type IV pili (Reisner et al.
2003). A collagen binding surface adhesion molecule, Sag, was reported in
Enterococcus spp. provides focal points for adherence and aggregation on eukaryotic cells, leading to biofilm formation. Staphylococcus epidermidis and
Staphylococcus aureus express several different types of microbial surface components recognizing adhesive matrix molecule (MSCRAMMs: ~12 in S. epidermidis
and ~ 20 in S. aureus) that have ability to bind to host matrix proteins including
fibronectin and fibrinogen (Fey and Olson 2010).
7.2.4 Surface Adhesins That Contribute to biofilm Structure
Maturation stage of the biofilm leads to the three dimensional mushroom like cell
growth surrounding fluid filled channels. It is characterized intercellular aggregation, which involves many different adhesive proteins or polysaccharide based exopolymers. Mostly as a consequence of bacterium-bacterium interactions, a
heterogeneous physicochemical environment is created wherein bacteria shows
traits distinguished from their planktonic counterparts (Romeo 2008).
An autotransporter protein Antigen 43 encoded by flu locus, is found in many
strains of E. coli, it and other SAAT: self associating autotransporter proteins,
including AIDA-I and TibA impair bacterial motility to mediate attachment to the
surface and also aids in intercommunication between the bacteria of same species
(Ulett et al. 2007). Moreover, in urinary tract infections (UTI), E. coli cells that form
biofilm like structures within bladder cells overexpress Ag43 (Anderson et al. 2003).
B. P. Singh et al.
7.2.3 Fimbriae Affect the Irreversible Adhesion to Surfaces
In case of biotic surfaces, bacterial attachment to the host surface is mediated via the
specific recognition of bacterial surface proteins by the extracellular proteins or
carbohydrate moieties expressed on surface of the cells/ tissues. In E. coli, three
categories of fimbriae strengthen the bacteria-to-surface interactions; type 1 fimbriae, curli, and conjugative pili. Type 1 fimbriae (or pili) are filamentous adhesins
produced by both commensal and pathogenic E. coli isolates. Type 1 pili can adhere
to wide range of eukaryotic surface receptors in mannose dependent manner. Type
1 pili tip adhesin, Fim H, binds to eukaryotic mannose oligosaccharides and is
involved in pathogenesis caused by uropathogenic E. coli. Moreover, curli fimbriae,
also called thin aggregative fimbriae, were initially identified in E. coli, are also
produced by other Enterobacteriaceae such as Shigella, Citrobacter, and
Enterobacter. Curli bind to eukaryotic proteins such as fibronectin, laminin and
plasminogens, to promote adhesion to eukaryotic host. Curli production is encoded
by two sets of divergently transcribed operons: csgBA (structural components of
curli fimbriea) and csgDEFG (regulatory and export machinary of curli) (Ben Nasr
et al. 1996). Researchers showed that F conjugative pilus could functionally substitute for Ag43, curli or type 1 fimbriea. In Pseudomonas aeruginosa, attachment and
movement through the viscous cell surface is aided by type IV pili (Reisner et al.
2003). A collagen binding surface adhesion molecule, Sag, was reported in
Enterococcus spp. provides focal points for adherence and aggregation on eukaryotic cells, leading to biofilm formation. Staphylococcus epidermidis and
Staphylococcus aureus express several different types of microbial surface components recognizing adhesive matrix molecule (MSCRAMMs: ~12 in S. epidermidis
and ~ 20 in S. aureus) that have ability to bind to host matrix proteins including
fibronectin and fibrinogen (Fey and Olson 2010).
7.2.4 Surface Adhesins That Contribute to biofilm Structure
Maturation stage of the biofilm leads to the three dimensional mushroom like cell
growth surrounding fluid filled channels. It is characterized intercellular aggregation, which involves many different adhesive proteins or polysaccharide based exopolymers. Mostly as a consequence of bacterium-bacterium interactions, a
heterogeneous physicochemical environment is created wherein bacteria shows
traits distinguished from their planktonic counterparts (Romeo 2008).
An autotransporter protein Antigen 43 encoded by flu locus, is found in many
strains of E. coli, it and other SAAT: self associating autotransporter proteins,
including AIDA-I and TibA impair bacterial motility to mediate attachment to the
surface and also aids in intercommunication between the bacteria of same species
(Ulett et al. 2007). Moreover, in urinary tract infections (UTI), E. coli cells that form
biofilm like structures within bladder cells overexpress Ag43 (Anderson et al. 2003).
B. P. Singh et al.