LYSINE IRON AGAR SLANT (10 Slants)

Lysine Iron Agar (LIA) is a differential culture medium employed for the detection of enteric pathogens, especially Salmonella spp., and identification through lysine decarboxylase or lysine deaminase activity and the production of hydrogen sulphide (H2S). LIA is routinely used in clinical, food, environmental and research laboratories to differentiate Enterobacteriaceae.

Lysine Iron Agar (LIA), originally developed by Edwards and Fife, was developed to aid in the identification of lactose and non-lactose utilizing Salmonella spp. Some strains of Salmonella are capable of rapid fermentation of lactose which may inhibit hydrogen sulphide production on other differential media and thus may lead to false-negative results. The utilization of lysine and specific indicators in the formulation of it aids in further differentiation and identification of the organisms.

As per the formulation it consists of peptone and yeast extract which supply the nutrients needed to sustain growth. Dextrose is the fermentable carbohydrate, whilst ferric ammonium citrate and sodium thiosulphate allow the clouding of hydrogen sulphide to be identified. The production of H2S is identified by the characteristic black precipitate of ferrous sulphide.

The medium can also be used to differentiate organisms based on their ability to ferment/ metabolise lysine. If an organism can decarboxylate the amino acid lysine, it is converted into free amine, leading to the production of cadaverine. This produces an alkaline reaction, causing a purple colour change in the medium.

If the organism produces acidic by-products in its metabolism of lysine, it produces a yellow butt. Lysine deamination produces a reddish brown colour change on the surface of the slant.

Lysine Iron Agar is used as an adjunct to Triple Sugar Iron (TSI) Agar to enhance the differentiation of Salmonella and Shigella, Escherichia coli and other enteric organisms, due to its accuracy and simplicity of interpretation as an aid to investigation and quality control testing.

Lysine Iron Agar (LIA) is a differential medium used to identify enteric bacteria, including Salmonella, through lysine decarboxylase activity, lysine deaminase activity and H2S (hydrogen sulphide) production. The medium itself contains peptone, yeast extract, dextrose, ferric ammonium citrate and sodium thiosulphate to grow the bacteria. The production of H2S is indicated by black precipitate, whilst the progression of the bacteria through metabolism of lysine results in the medium changing colour. Lysine Iron Agar is commonly used in clinical, food and research laboratories in conjunction with Triple Sugar Iron Agar in order to identify enteric pathogens.