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Journal of Biomedical Optics

Optical interference probe of biofilm hydrology: label-free characterization of the dynamic hydration behavior of native biofilms
Author(s): Richard T. McDonough; Hewen Zheng; Mercy A. Alila; Jerry Goodisman; Joseph Chaiken
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Paper Abstract

Biofilm produced by Escherichia coli (E. coli) or Pseudomonas aeruginosa (P. aeruginosa) on quartz or polystyrene is removed from the culture medium and drained. Observed optical interference fringes indicate the presence of a layer of uniform thickness with refractive index different from air-dried biofilm. Fringe wavelengths indicate that layer optical thickness is < 20    μ m or 1 to 2 orders of magnitude thinner than the biofilm as measured by confocal Raman microscopy or fluorescence imaging of the bacteria. Raman shows that films have an alginate-like carbohydrate composition. Fringe amplitudes indicate that the refractive index of the interfering layer is higher than dry alginate. Drying and rehydration nondestructively thins and restores the interfering layer. The strength of the 1451-nm near infrared water absorption varies in unison with thickness. Absorption and layer thickness are proportional for films with different bacteria, substrates, and growth conditions. Formation of the interfering layer is general, possibly depending more on the chemical nature of alginate-like materials than bacterial processes. Films grown during the exponential growth phase produce no observable interference fringes, indicating requirements for layer formation are not met, possibly reflecting bacterial activities at that stage. The interfering layer might provide a protective environment for bacteria when water is scarce.

Paper Details

Date Published: 8 March 2017
PDF: 13 pages
J. Biomed. Opt. 22(3) 035003 doi: 10.1117/1.JBO.22.3.035003
Published in: Journal of Biomedical Optics Volume 22, Issue 3
Show Author Affiliations
Richard T. McDonough, Syracuse Univ. (New York)
Hewen Zheng, Syracuse Univ. (New York)
Mercy A. Alila, Syracuse Univ. (New York)
Jerry Goodisman, Syracuse Univ. (New York)
Joseph Chaiken, Syracuse Univ. (New York)

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