Antibiofilm polysaccharides

Abstract

Bacterial extracellular polysaccharides have been shown to mediate many of the cell-to-cell and cell-to-surface interactions that are required for the formation, cohesion and stabilization of bacterial biofilms. However, recent studies have identified several bacterial polysaccharides that inhibit biofilm formation by a wide spectrum of bacteria and fungi both in vitro and in vivo. This review discusses the composition, modes of action and potential biological roles of antibiofilm polysaccharides recently identified in bacteria and eukarya. Some of these molecules may have technological applications as antibiofilm agents in industry and medicine.

Fig. 1. Properties of antibiofilm polysaccharides

(A) Biofilm formation by E. coli K12 MG1655 F+ on glass spatulas in a continuous flow biofilm microfermentor (top) or in microtiter plate wells (bottom) in the presence of fresh media (control), E. coli CFT073 supernatant, or K2 group II capsule mutant (ΔkpsD) supernatant. (B) Biofilm formation by S. epidermidis, S. aureus and K. kingae in microtiter plate wells in the absence or presence of K. kingae colony biofilm extract. (C) S. aureus biofilm formation in the presence of K. kingae colony biofilm extract or broth culture supernatant shows that PAM galactan is preferentially released within biofilms.

Fig. 2. Mode of action of antibiofilm polysaccharides

(A) Alteration of abiotic surfaces. Determination of the surface contact angle of a drop of water on untreated (double-distilled water [dH₂O]), K2 group II capsule or Ec300p-treated microscope slides showed an increased hydrophilicity of the surfaces (B) Surface coating. Biofilm formation by S. epidermidis on polystyrene surfaces coated with K. kingae colony biofilm extract. The extract forms an anti-adhesive layer where it contacted the surface. (C) Alteration of biotic surfaces. GFP-tagged E. coli K12 was inoculated in a flow cell and monitored by confocal microscopy. Addition of K2 culture supernatant after 2 hours of growth shows an alteration of development of K12 biofilm after 20 hours of growth.

Fig. 3. Biological roles and potential applications of anti-adhesion polysaccharides

BIOLOGICAL ROLES. (A) Competition. Anti-adhesion polysaccharides can inhibit biofilm formation or enhance biofilm dispersal. They are also involved in colonization resistance against invading or competing bacteria, hence providing an ecological advantage to the producer bacteria. (B) Anti-adhesion polysaccharides are secreted into the extracellular medium. Bacteria producing such polysaccharides can be also susceptible to their own antibiofilm polysaccharide and therefore self-regulate their adhesion behavior. (C) Competing bacteria can sense secreted anti-adhesion polysaccharides and respond to it by altering their own gene expression, for instance, by downregulating expression of their adhesion factors. POTENTIAL APPLICATIONS. (D) Adjuvant. Several studies point out that anti-adhesion polysaccharides enhance antibiotic functions when administered together. For instance, they can rupture cell-to-cell interactions, rendering antibiotic effect more efficient. (E) Anti-adhesive coating. surfaces coated or grafted with anti-adhesion polysaccharides could be used on indwelling medical devices (here, totally implanted veinous catheters and silicone tubing) or industrial settings (here industrial tubes). (F) Prebiotic/Probiotic. Bacteria producing anti-adhesion polysaccharides could be used as probiotics in order to outcompete pathogens, for instance in the gastro-intestinal tract. Moreover, biodegradable oligosaccharides are currently used as prebiotics to confer health advantages.