Remel™ Modified Lysine Iron Agar

Selectively isolate Salmonella species using Thermo Scientific™ Remel™ Modified Lysine Iron Agar (Dehydrated). Edwards and Fifa developed lysine iron agar (LIA) to detect rapidly fermenting lactose positive Arizona strains¹. Based on the production of hydrogen sulfide (H₂S), LIA was modified by Rappold and Bolderdijk by adding novobiocin, bile salts, lactose, and sucrose for selective and differential isolation of Salmonella spp.² and was called Modified Lysine Agar (MLIA). It is recommended by the American Public Health Association (APHA) for isolation of Salmonella from food products^3,4.

Modified LIA medium is recommended for use in qualitative procedures for selective isolation of Salmonella spp. from food samples. The United States Department of Agriculture (USDA) also observed superior recovery of Salmonella from fresh and cured meat using MLIA as compared to other selective and differential media. This medium uses lysine as the substrate for detection of the enzyme lysine decarboxylase produced by Salmonella.

• Selective medium – Novobiocin inhibits gram-positive organisms such as staphylococci.
• Recommended by the American Public Health Association(APHA) to isolate Salmonella from food products^3,4.
• Easy to interpret
  1. H₂S Production
     • Positive test – Black precipitate
     • Negative test – No black color development
  2. Lysine Decarboxylation
     • Positive test – Purple colonies
     • Negative test – Yellow colonies

MLIA has lactose and sucrose as the source of fermentable carbohydrates. Sodium thiosulfate and ferric ammonium citrate help in the detection of H₂S-positive Salmonella. Lysine acts as a substrate for detection of lysine decarboxylase. Novobiocin is added as the selective agent which inhibits gram-positive organisms such as staphylococci.

When Salmonella spp. decarboxylate lysine, the amine is converted to cadaverine, which has an alkaline pH, and the medium remains purple. Salmonella form colonies which are purple with black centers. Enteric gram-negative bacilli like Proteus spp. produce H₂S, but they do not decarboxylate lysine and form yellow colonies. Citrobacter freundii have been found to mimic salmonellae on this medium.