Lysine Iron Agar Test- Principle, Media, Procedure, Results, Uses


Lysine iron agar (LIA) test is a biochemical test that is used to differentiate gram-negative bacilli based on their ability to decarboxylate or deaminate lysine and to produce hydrogen sulfide (H2S). Lysine is an amino acid that can undergo two different metabolic pathways: decarboxylation and deamination. Decarboxylation is the removal of a carboxyl group from lysine, resulting in the formation of cadaverine, an alkaline compound. Deamination is the removal of an amino group from lysine, resulting in the formation of alpha-ketocarboxylic acid, which can react with iron to produce a reddish-brown compound. Hydrogen sulfide is a gas that can be produced by some bacteria from the reduction of sulfur-containing compounds, such as sodium thiosulfate. Hydrogen sulfide can react with iron to form a black precipitate of ferrous sulfide.

The LIA test can help to identify and differentiate various members of the Enterobacteriaceae family, such as Escherichia coli, Salmonella spp., Shigella spp., Proteus spp., and Citrobacter spp., as well as some other gram-negative bacilli, such as Morganella morganii and Providencia spp. The LIA test can also be used to distinguish between different serotypes of Salmonella enterica, such as Typhi, Paratyphi A, Paratyphi B, and Paratyphi C. The LIA test is simple, inexpensive, and easy to perform and interpret. It can provide valuable information for the diagnosis and treatment of infections caused by gram-negative bacilli.