Role of capsular colanic acid in adhesion of uropathogenic Escherichia coli

Abstract

Urinary tract infections are the most common urologic disease in the United States and one of the most common bacterial infections of any organ system. Biofilms persist in the urinary tract and on catheter surfaces because biofilm microorganisms are resistant to host defense mechanisms and antibiotic therapy. The first step in the establishment of biofilm infections is bacterial adhesion; preventing bacterial adhesion represents a promising method of controlling biofilms. Evidence suggests that capsular polysaccharides play a role in adhesion and pathogenicity. This study focuses on the role of physiochemical and specific binding interactions during adhesion of colanic acid exopolysaccharide mutant strains. Bacterial adhesion was evaluated for isogenic uropathogenic Escherichia coli strains that differed in colanic acid expression. The atomic force microscope (AFM) was used to directly measure the reversible physiochemical and specific binding interactions between bacterial strains and various substrates as bacteria initially approach the interface. AFM results indicate that electrostatic interactions were not solely responsible for the repulsive forces between the colanic acid mutant strains and hydrophilic substrates. Moreover, hydrophobic interactions were not found to play a significant role in adhesion of the colanic acid mutant strains. Adhesion was also evaluated by parallel-plate flow cell studies in comparison to AFM force measurements to demonstrate that prolonged incubation times alter bacterial adhesion. Results from this study demonstrate that the capsular polysaccharide colanic acid does not enhance bacterial adhesion but rather blocks the establishment of specific binding as well as time-dependent interactions between uropathogenic E. coli and inert substrates.

FIG. 1.

SEM micrograph of an AFM cantilever tip coated with E. coli C97 bacteria.

FIG. 2.

AFM force-versus-distance curves of E. coli C97 bacteria interacting with hydrophilic glass. (A) CPS⁺ (+), CPS wild-type (•), and CPS⁻ (▵) strains in PBS buffer. (B) The CPS⁻ strain interacting with glass in PBS (▵), PBS plus 100 mM NaCl (▪), and PBS plus 1,000 mM NaCl (∗).

FIG. 3.

AFM force-versus-distance curves of E. coli C97 bacteria interacting with hydrophobic OTS-treated glass. The CPS⁺ (+), CPS wild-type (•), and CPS⁻ (▵) strains were evaluated in PBS buffer.

FIG. 4.

AFM force-versus-distance curves of E. coli C97 bacteria interacting with hydrophobic silicone in PBS buffer. Interactions with spun-coated silicone were evaluated in CPS⁺ (+), CPS wild-type (•), and CPS⁻ (▵) strains.

FIG. 5.

Photographs of E. coli bacteria adhering to hydrophobic OTS-treated glass in PBS buffer in the parallel-plate flow cell apparatus.