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Use of episcopic differential interference contrast microscopy to identify bacterial biofilms on salad leaves and track colonization by Salmonella Thompson

Warner, J.C., Rothwell, S.D. and Keevil, C.W. (2008) Use of episcopic differential interference contrast microscopy to identify bacterial biofilms on salad leaves and track colonization by Salmonella Thompson Environmental Microbiology, 10, (4), pp. 918-925. (doi:10.1111/j.1462-2920.2007.01511.x).

Record type: Article


Zoonotic pathogens such as Salmonella can cause gastrointestinal illness if they are ingested with food. Foods such as salads pose a greater risk because they are consumed raw and have been the source of major outbreaks of disease from fresh produce. The novel light microscopy methods used in this study allow detailed, high resolution imaging of the leaf surface environment (the phyllosphere) and allow pathogen tracking. Episcopic differential interference contrast microscopy coupled with epifluorescence was used to view the natural microflora in situ on salad leaves and their topographical distribution.
Fluorescent nucleic acid staining was used to differentiate between bacterial colonists and inorganic debris. Salmonella enterica serovar Thompson expressing green fluorescent protein was inoculated onto individual spinach leaves for 24 h at 22°C in order to observe spatial and temporal patterning of colonization on the two surfaces of each leaf under different osmotic conditions. The results obtained show that salad leaves are host to high numbers of bacteria, typically 105 per square millimetre. Cells are present in complex three-dimensional aggregations which often have a slimy appearance, suggesting the presence of biofilms. Washing of the leaves had little effect on the number of adherent pathogens, suggesting very strong attachment. Episcopic differential interference contrast microscopy is a rapid alternative to both scanning electron microscopy and confocal laser scanning microscopy for visualizing leaf topography and biofilm formation in the natural state.

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e-pub ahead of print date: 6 January 2008
Published date: April 2008
Organisations: Centre for Biological Sciences


Local EPrints ID: 209325
ISSN: 1462-2920
PURE UUID: 9f5929b7-6eea-4b4a-8b0f-80d3a66c850e
ORCID for C.W. Keevil: ORCID iD

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Date deposited: 30 Jan 2012 15:22
Last modified: 18 Jul 2017 10:47

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Author: J.C. Warner
Author: S.D. Rothwell
Author: C.W. Keevil ORCID iD

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