Eosin Methylene Blue Agar was first developed by Holt-Harris and Teague. This formula contains both lactose and sucrose with the two indicator dyes, eosin Y and methylene blue. Escherichia and Enterobacter species can be easily distinguished from other Gram negative enteric bacilli using this medium. EMB Agar contains two mildly selective dyes, eosin Y and methylene blue, which interact under strong acidic conditions to impart metallic sheen to Escherichia coli colonies. In addition, E coli produces dark blue-black colonies. Other coliforms produce mucoid, pinkish brown colonies. Non-lactose fermenting bacteria Salmonella and Shigella, produce translucent or colorless colonies. Acinetobacter, Aeromonas, Pseudomonas, Plesiomonas and Yersinia also grow on this medium. Gram-positive bacteria are inhibited by eosin Y. The slow lactose fermenters also ferment sucrose which reduces the incidence of false-positive interpretations. Eosin Methylene Blue Agar is used for the isolation and identification of Gram negative enteric bacteria. (Alpha Biosciences # E05-102-500gm)
Use: Eosin Methylene Blue Agar is used for the isolation and identification of Gram negative enteric bacteria.
Description: Eosin Methylene Blue Agar was first developed by Holt-Harris and Teague. This formula contains both lactose and sucrose with the two indicator dyes, eosin Y and methylene blue. Escherichia and Enterobacter species can be easily distinguished from other Gram negative enteric bacilli using this medium. EMB Agar contains two mildly selective dyes, eosin Y and methylene blue, which interact under strong acidic conditions to impart metallic sheen to Escherichia coli colonies. In addition, E coli produces dark blue-black colonies. Other coliforms produce mucoid, pinkish brown colonies. Non-lactose fermenting bacteria Salmonella and Shigella, produce translucent or colorless colonies. Acinetobacter, Aeromonas, Pseudomonas, Plesiomonas and Yersinia also grow on this medium. Gram-positive bacteria are inhibited by eosin Y. The slow lactose fermenters also ferment sucrose which reduces the incidence of false-positive interpretations.
Formula* per Liter
- Pancreatic Digest of Gelatin ........ 10.0g
- Lactose ......................................... 5.0g
- Dipotassium Phosphate ................. 2.0g
- Sucrose ......................................... 5.0g
- Eosin Y .............................................. 0.4g
- Methylene Blue ......................... 0.065g
- Agar ............................................. 13.5g
Final pH: 7.2 ± 0.2 at 25.0°C
* Grams per liter may be adj. or formula supplemented to obtain desired performance
Preparation: Mix 36 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for one minute to dissolve completely. Distribute and autoclave at 121°C for 15 minutes. Cool to 45-50°C and mix thoroughly before pouring plates.
Quality Control Specifications:
- The powders are homogeneous, free flowing and light reddish-purple.
- Visually the prepared medium is clear to slightly hazy and dark bluish purple to reddish purple.
- Expected cultural response after 18-24 hours at 35.0°C.
Organism                                                                                  Result
Enterococcus faecalis ATCC 29212Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Partial Inhibition, colorless
Escherichia coli ATCC 25922                        Growth, blue-black colonies with dark       Â
                                                                                    center and metallic sheen.
Salmonella typhimurium ATCC 14028Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Growth, colorless colonies
Storage: Store the sealed bottle containing the dehydrated medium at 2 to 30.0°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original reddish-purple.
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