Cranberry juice has long been believed to benefit the prevention and treatment of urinary tract infections (UTIs). As the first step in the development of infection, bacterial adhesion is of great research interest, yet few studies have addressed molecular level adhesion in this context. P-fimbriated Escherichia coli play a major role in the development of a serious type of UTI, acute pyelonephritis. Experiments were conducted to investigate the molecular-scale effects of cranberry juice on two E. coli strains: HB101, which has no fimbriae, and the mutant HB101pDC1 which expresses P-fimbriae. Atomic force microscopy (AFM) was used to investigate both bacterial surface characteristics and adhesion forces between a probe surface (silicon nitride) and the bacteria, providing a direct evaluation of bacterial adhesion and interaction forces. Cranberry juice affected bacterial surface polymer and adhesion behavior after a short exposure period (<3 h). Cranberry juice affected the P-fimbriated bacteria by decreasing the adhesion forces between the bacterium and tip and by altering the conformation of the surface macromolecules on E. coli HB101pDC1. The equilibrium length of polymer (P-fimbriae) on this bacterium decreased from approximately 148 to approximately 48 nm upon being exposed to cranberry juice. Highly acidic conditions were not necessary for the prevention of bacterial adhesion, since neutralization of cranberry juice solutions to pH = 7.0 allowed us to observe differences in adhesion between the E. coli strains. Our results demonstrate molecular-level changes in the surfaces of P-fimbriated E. coli upon exposure to neutralized cranberry juice.

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Staphylococcus epidermidis is among the most commonly isolated microbes from medical implant infections, particularly in the colonization of blood-contacting devices. We explored the relationships between surface wettability and root-mean-square roughness (Rq) on microbial adhesive strength to a substrate. Molecular-level interactions between S. epidermidis and a variety of chemically and texturally distinct model substrata were characterized using a cellular probe and atomic force microscopy (AFM). Substrata included gold, aliphatic and aromatic self-assembled monolayers, and polymeric and proteinaceous materials. Substrate hydrophobicity, described in terms of the water contact angle, was an insufficient parameter to explain the adhesive force of the bacterium for any of the surfaces. Correlations between adhesion forces and Rq showed weak relationships for most surfaces. We used an alternate methodology to characterize the texture of the surface that is based on a fractal tiling algorithm applied to images of each surface. The relative area as a function of the scale of observation was calculated. The discrete bonding model (DBM) was applied, which describes the area available for bonding interactions over the full range of observational scales contained in the measured substrate texture. Weak negative correlations were obtained between the adhesion forces and the area available for interaction, suggesting that increased roughness decreases bacterial adhesion when nano- to micrometer scales are considered. We suggest that modification of the DBM is needed in order to include discontinuous bonding. The adhesive strength is still related to the area available for bonding on a particular scale, but on some very fine scales, the bacteria may not be able to conform to the valleys or pits of the substrate. Therefore, the bonding between the bacterium and substrate becomes discontinuous, occurring only on the tops of ridges or asperities.