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Levine EMB Agar
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| I. INTRODUCTION |
| Levine EMB Agar is a slightly selective and differential medium for the isolation, cultivation and differentiation of gram-negative enteric microorganisms isolated from both clinical and nonclinical specimens. It is widely used for the examination of materials of sanitary importance for the presence of coliforms. |
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PRODUCT INFORMATION
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| II. INTENDED USE |
| Levine EMB Agar is a selective and differential plating medium for isolation of gram-negative enteric bacteria. |
| III. SUMMARY AND EXPLANATION |
| Shortly following the publication by Holt-Harris and Teague of a paper
describing a new culture medium for the differentiation of enteric microorganisms
through the use of eosin and methylene blue dyes, Levine described a modification
of their formulation which he claimed gave better differentiation between
what are now referred to as Escherichia and Enterobacter species. The two
formulations differ in that Levine EMB Agar does not contain sucrose. Both
of these formulations were developed to improve upon the differentiating
properties of Endo Agar, which was developed previously.
Levine EMB Agar utilizes dyes as selective agents. It is recommended for use in the microbiological examination of dairy products and foods by the American Public Health Association. |
| IV. PROCEDURE |
| Instructions The agar surface should be smooth and moist, but without excessive moisture. Streak the specimen as soon as possible after it is received in the laboratory. The streak plate is used primarily to isolate pure cultures from specimens containing mixed flora. A nonselective medium should also be streaked to increase the chance of recovery when the population of gram-negative organisms is low and to provide an indication of other organisms present in the specimen. Alternatively, if material is being cultured directly from a swab, roll the swab over a small area of the surface at the edge; then streak from this inoculated area. Incubate plates, protected from light, at 35 ± 2°C for 18 to 24 h. |
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Visual Results on This Medium Should
Be As Follows
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| After incubation most plates will show an area of confluent growth. Because
the streaking procedure is, in effect, a "dilution" technique,
diminishing numbers of microorganisms are deposited on the streaked areas.
Consequently, one or more of these areas should exhibit isolated colonies
of the organisms contained in the specimen. Better isolation is obtained
due to the inhibitory action of the medium.
Typical colonial morphology on Levine EMB Agar is as follows: |
| E. coli . . . . . . . . . . . . Large, blue-black, green
metallic sheen Enterobacter/Klebsiella . . . . . . Large, mucoid, blue-black Proteus . . . . . . . . . . . . Large, colorless Salmonella . . . . . . . . . . . Large, colorless Shigella . . . . . . . . . . . . Large, colorless Pseudomonas . . . . . . . . . . Irregular, colorless Gram-positive bacteria . . . . . . No growth to slight growth |