The use of force-volume microscopy to examine bacterial attachment to titanium surfaces
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Force-volume microscopy (FVM) was used to study the interfacial and adhesive forces affecting primary bacterial attachment to surfaces. Forces were measured for titanium surfaces immersed either in cation-enriched (CE) solutions of yeast extract amended with phosphate buffer or in control solutions lacking the cation enrichment. The FVM measurements demonstrated that regions of elevated interfacial repulsion covered 72(±2)% of the surfaces immersed in CE solutions, compared to 26(±2)% for immersion in control solutions. Parallel collection of scanning electron micrographs demonstrated that surface densities of attached Pseudomonas aeruginosa were approximately 0.62(±1.3) × 106 cells cm−2 compared to 8.7(±0.8) × 106 cells cm−2 for surfaces immersed in the CE and control solutions, respectively. Interfacial repulsion indicated by FVM measurements therefore served as a predictor of bacterial attachment. Another factor influencing bacterial attachment was the adhesion force. FVM measurements indicated that the upper fifth percentile of surface adhesion was 1784(±40) pN for surfaces immersed in the CE solution compared to 2284(±40) pN for the control solutions. The more extensive regions of elevated interfacial repulsion as well as of decreased surface adhesion provide an explanation for the lower density of attached cells observed for the surfaces immersed in the CE compared to the control solutions. The conclusion is that FVM is a sensitive and informative technique that can be used to measure and explain interactions between microorganisms and surfaces.
KeywordsForce-volume microscopy Atomic force microscopy Pseudomonas aeruginosa Interfacial forces Surface adhesion
We are grateful for support received from the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences in the US Department of Energy and a gift from the Akatsuka Group, Japan to Harvard School of Engineering and Applied Sciences. We thank Dingding An at the Harvard Medical School for helpful discussion.