From Big Medical Encyclopedia

LEVINA WEDNESDAY (M. Levine, amer. bacteriologist, sort. in 1889; synonym agar with eosine and methylene blue) — a color elective medium for differentiation of bacteria this. Enterobacteriaceae, is used at laboratory diagnosis of dysentery, typhoid, salmonelloses and other intestinal infections. For the first time the agar with eosine and methylene blue was offered in 1916 Holt-Harris and Tigom (J. E. Holt-Harris, O. of Teague), later, in 1918, structure of the environment was modified by Levin.

Hp along with other solid color differential and diagnostic nutrient mediums for enterobakteriya found broad application in a lab. to practice. With its help it is possible to find pathogenic laktozonegativny microflora in rather big percent of cases. Ready Hp is quite stable, does not change the properties on light or at storage for several days; at its production exact establishment of concentration of hydrogen ions (pH) is not required. Hp which are a part organic dyes selectively detain growth of gram-positive bacteria thanks to what it at the same time is the environment of enrichment and yields relatively the best results at direct crops of the studied material even if it contains rather trace amount of pathogenic bacteriums.

Depending on quality of separate ingredients (peptone and in particular dyes) the results received on Hp can vary a little therefore at production of each new series of the environment use of materials of the same brand is desirable that considerably facilitates recognition of colonies.

Several copy-books and ways of preparation of Hp are known (Yu. A. Kozlov, G. Ya. Sinay, O. G. Birger, etc.). The greatest distribution was gained by a way, at Krom separately prepare the main environment, solutions of lactose and dyes suitable for preservation for the future and mixed before the use.

The main environment consists of 10 g of bacteriological peptone, 15 g an agar agar, 2 g of potassium phosphate of disubstituted (K2HPO4) and 1 l of a distilled water. It will be sterilized in the autoclave at 1 at 15 — 20 min., pH do not correct.

At preparation of the differential environment on each 100 ml of the melted main environment at constant stirring add prepared on a distilled water and previously sterilized by fluid steam (fractionally, 3 days in a row 15 — 20 min.) the following solutions in the given sequence of 5 ml of 20% of solution of medical lactose, 2 ml of 2% of solution of eosine of alkaline (bacteriological), 1,5 ml of 0,5% of solution of methylene blue. The ready environment is spilled in Petri dishes, slightly dried and used as usual. Color of the environment blue-violet.

Colonies of colibacillus on Hp small, roundish, with a smooth brilliant surface, dark blue (to black) colors, sometimes with metallic luster. Young colonies rather turbid, opaque, can be painted only in the center. Colonies of causative agents of dysentery, a typhoid and paratyphus rather smaller, round, brilliant and transparent, usually absolutely colourless (young people) or with a subtle pinkish or bluish shade. Colonies a protea of creeping growth do not give; they are small, isolated, orange-yellow color. Wednesday changes the color only around colonies a protea.

Some authors recommend to increase the number of 0,5% of solution methylene blue to 2 ml by 100 ml of the main environment or to exclude the phosphatic buffer from its structure. It is possible to prepare Wednesday not with peptone, and on the basis of Hottinger's repitch, at pH 7,2 — 7,3 with addition of the quantity of an agar and potassium phosphate corresponding to a copy-book. Use of meat water for preparation of the environment is inadmissible, differentiation of colonies in this case considerably worsens.

The way of preparation of dry Hp, very stable on quality and especially convenient for long-term storage and in the conditions of forwarding work is known (N. V. Ploskirev).

Stable dry Hp is produced the industry, the instruction for its production and use is distributed together with Wednesday. Most diagnostic laboratories applies to allocation and differentiation of pathogenic enterobakteriya high-quality standard elective dry mediums of domestic production — Hp, baktoagar, Ploskirev's circle (see. Ploskireva Wednesday ).

See also Differential and diagnostic environments , Mediums .

Bibliography: The guide to microbiological diagnosis of infectious diseases, under the editorship of K. I. Matveev, page 110, M., 1973; The Reference book on microbiological and virologic methods of a research, under the editorship of M. O. Birger, page 58, M., 1973; Levine M. The effect of concentration of dyes on differentiation of enteric bacteria on eosin-methylene-blue agar, J. Bact., v. 45, p. 471, 1943.

G. P. Belikov.