Levina Wednesday (M. Levine; synonym for eosin-methyleneblau agar) is a colored elective nutrient medium used to differentiate intestinal microorganisms in the microbiological diagnosis of intestinal infections - typhoid, salmonella, dysentery, colienteritis. Stable when stored for several days. The presence in the environment of lactose allows you to secrete pathogens that can not decompose this carbohydrate. Organic dyes in Levin’s medium retard the growth of saprophytes, which allows the medium to be used for direct seeding of the material under study.
To obtain stable results, it is recommended to use ingredients of the same brand when making Levin's medium. It is most convenient to separately prepare the basic medium, solutions of lactose and dyes. The specified ingredients are prepared for the future and mixed before use.
The main medium: 1) bacteriological peptone - 10 g; 2) agar-agar - 15 g; 3) dibasic potassium phosphate (K 2 HPO 4 ) - 2 V; 4) distilled water - 1 l. Pour 100 ml of each and sterilize at 120 ° for 15-30 minutes.
Differential medium: for every 100 ml of molten basic medium, the following solutions are added with stirring; they are prepared in distilled water and sterilized by fractional flowing steam for three consecutive days. Ingredients: 1) 20% lactose solution — 5 ml; 2) 2% bacteriological eosin solution - 2 ml; 3) 0.5% solution of methylene blue - 1.5 ml. Wednesday poured into Petri dishes, dried. The finished medium has a blue-purple color. In the absence of peptone, the medium can be prepared on the basis of Hottinger's par (pH = 7.2-7.3). The dry environment of Levin, produced by industry, has found wide application.
Pathogenic bacteria - causative agents of typhoid fever, salmonellosis, dysentery - do not decompose lactose, grow on Levin's medium in the form of small, round, transparent, often colorless colonies, sometimes with a pinkish or bluish tinge. E. coli forms on the environment of Levin small smooth colonies of dark blue color. In young colonies, coloring can be observed only in the center. Proteus grows in small orange-yellow colonies, the color of the environment around the colonies changes.
Colonies of other bacteria do not give a similar picture.
See also Differential diagnostic media, Nutrient media.