What color is a positive EMB result?
What color is a positive EMB result?
In the completed test an EMB positive colony (dark, metallic color) is used to inoculate a tube of lactose broth to verify acid and gas production. A nutrient agar slant is also generally inoculated and serves as a source for stains to confirm the Gram-negative, non-spore-forming nature of coliforms.
Is E coli positive for EMB?
In EMB agar, most of the strains of E. coli colonies have a characteristic green sheen. Rapid fermentation of lactose & production of strong acids, thus a rapid reduction in the pH of the EMB agar the critical factor in the formation of the green metallic sheen observed with E. The colonies will be colorless.
What does green on EMB agar mean?
Escherichia coli, a vigorous fermenter, often produces a green metallic sheen. Normally-colored or colorless colonies indicate that the organism ferments neither lactose nor sucrose and is not a fecal coliform. Escherichia coli often produces a metallic green sheen on EMB.
What bacteria grows on EMB?
Colony morphology
| Organism | Colonial appearance on EMB agar |
|---|---|
| Enterobacter aerogenes | Colonies are 4-6mm in diameter, raised and mucoid, tending to become confluent. No metallic sheen, grey-brown centers by transmitted light |
| Salmonella and Shigella spp | Translucent and colorless colonies |
| Pseudomonas spp | Colorless irregular colonies |
How EMB media differentiate bacteria?
Differentiation of enteric bacteria is possible due to the presence of the sugars lactose and sucrose in the EMB agar and the ability of certain bacteria to ferment the lactose in the medium. This metallic green sheen is an indicator of vigorous lactose and/or sucrose fermentation ability typical of fecal coliforms.
Is EMB Agar defined?
Eosin methylene blue agar (EMB) is an undefined medium. EMB is a complex medium consisting of peptone, dipotassium phosphate, lactose, eosin Y (dye), and agar. In Undefined media, the exact biochemical composition of the nutrient is not known and provides the growth of wide varieties of microorganisms.
What is the difference between EMB agar and MacConkey agar?
EMB agar and MacConkey agar are differential and selective media. The selective components in EMB agar are eosin and methylene blue dyes, whereas crystal violet dye and bile salts are the selective components in MacConkey agar. Lactose is the differential component in both media.
Is EMB agar selective or differential or both?
Eosin Methylene Blue (EMB) agar is both selective and differential. It contains the dyes eosin and methylene blue, which inhibit the growth of gram-positive bacteria and therefore select for gram-negative bacteria.
What type of bacteria does EMB agar favor?
EMB agar is a selective culture medium for Gram-negative bacteria. It is primarily used for isolation and differentiation of lactose fermenting (forms coloured colonies) and non-lactose fermenting (form colourless colonies) enteric bacilli.
Which of these bacteria will grow on EMB agar?
Only gram-negative bacteria grow on EMB agar. Gram-positive bacteria are inhibited by the dyes eosin and methylene blue added to the agar. Because of vigorous fermention of lactose and producion of large quantities of acid, colonies of Escherichia coli appear dark and blue-black with a metallic green sheen.
