Investigating Bacterial Outer Membrane Polymers and Bacterial Interactions with Organic Molecules Using Atomic Force Microscopy

Atabek, Arzu

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Investigating Bacterial Outer Membrane Polymers and Bacterial Interactions with Organic Molecules Using Atomic Force Microscopy

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The adhesion of bacteria to surfaces has been analyzed in terms of surface charge, surface energy, and the characteristics of polymers on bacteria, to understand the factors that control bacterial adhesion. Pseudomonas aeruginosa has received a great deal of interest because it is responsible for a variety of chronic bacterial infections such as airway infections in cystic fibrosis patients and ulcerative bacterial keratitis in soft contact lens users. Over the past few years, force measurement techniques such as atomic force microscopy (AFM) have made it possible to examine interactions between colloidal particles and surfaces. In the present study, the AFM was used to study the interactions between each of two Pseudomonas aeruginosa strains with proteins. Topographical images and force cycles of bacterial cells and proteins were analyzed. Bovine serum albumin (BSA) and concanavalin A (Con A) were the model proteins chosen to represent protein molecules that might affect bacterial adhesion. In addition, the role of LPS structure in bacterial adhesion was investigated. The magnitude of adhesive forces for two P. aeruginosa stains was not statistically significant when they interact with silicon. Although it is not clear if the pull-off distances are accurate representatives of the absolute length of bacterial surface molecules, the trend indicates that the surface molecules of strain AK1401 are shorter than those of strain PAO1. The semi-rough strain AK1401 was more hydrophobic than the smooth strain PAO1, according to the water contact angle measurements. However, surface free energy components and zeta potential values were not significantly different for both strains. Zeta potential of bacterial cells decreased when they were suspended in HEPES/DTT buffer instead of ultrapure water. The AFM results demonstrate the importance of nano-scale interactions between proteins and bacterial cells. Our results show that the lipid A and core oligosaccharides are the most important molecules influencing the interactions of P. aeruginosa with protein molecules. The interactions of P. aeruginosa with model proteins in our study were weak. Therefore, the role of protein molecules may be inadequate for the purpose of enhancing subsurface delivery for bioremediation. Our results suggest that the semi-rough mutant, AK1401, can adhere to the protein receptors of the epithelial cells or protein coated implants stronger than the smooth strain, PAO1, and therefore can cause serious infections.

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