Remel™ Lysine Iron Agar

Differentiate microorganisms based on lysine decarboxylase and hydrogen sulfide production using Thermo Scientific™ Remel™ Lysine Iron Agar (Dehydrated). In 1961, Lysine Iron Agar (Dehydrated) was developed to detect lactose positive Arizona strains implicated in outbreaks of food-borne disease¹. In 1966, Johnson et al. recommended LIA to help identify Salmonella spp². Later, Ewing recommended the use of LIA with TSI to detect enteric pathogens in routine examination of stools³.

Lysine as a substrate is used for detection of lysine decarboxylase and lysine deaminase. When Salmonella spp. decarboxylates lysine, the amine is converted to cadaverine resulting in a purple butt (alkaline). When Proteus spp. deaminates lysine, the amine is converted to α-ketocarboxylic acid resulting in the slant turning red.

Interpretation of test:

1. Lysine Decarboxylation (detected in butt)
   • Positive test – Purple slant/purple butt (alkaline), the butt reaction may be masked by H₂S production
   • Negative test – Purple slant/yellow butt (acid), fermentation of glucose only
2. Lysine Deamination (detected on slant)
   • Positive test – Red slant
   • Negative test – Slant remains purple
3. H₂S Production
   • Positive test – Black precipitate
   • Negative test – No black color development

The medium contains gelatin peptone and yeast extract that provide nitrogen, amino acids, and vitamins necessary for bacterial growth. Dextrose is the fermentable carbohydrate source and brom cresol purple is a pH indicator. Sodium thiosulfate and ferric ammonium citrate serve as indicators when H₂S is produced, resulting in a black precipitate in the butt of the tube.