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Lysine Iron Agar (LIA)
This agar is used as a diagnostic test for salmonellae. Salmonellae are the only group of Enterobacteriaceae that regularly decarboxylate lysin (by lysine decarboxylase) and produce large amounts of hydrogen sulphide. Bacteria that decarboxylate lysine cause an alkaline reaction (purple colour) throughout the medium. Those that do not, produce an alkaline slant and an acid butt (yellow) due to fermentation of glucose. Some bacteria may deaminate the lysine and produce a red slant and acid butt. Production of hydrogen sulphide causes a blackening in the medium due to formation of ferrous sulphide. The indicator is bromcresol purple.

1. Uninoculated medium.

2. Alkaline/alkaline/H2S: Salmonella.

3. Alkaline/yellow/H2S: Citrobacter.
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© Department of Veterinary Disease Biology 2011
Faculty of Health and Medical Sciences - University of Copenhagen