We got purple black, pink and white colonies on EMB agar plate. From that how we will detect E.coli.
Dear people, isn't it enough to repeat the same answer once?! Nomally you vote the same answer up! Or are you publishing the similar results that you generate in more than one journal? No! Thanks! Cheers, Nadine
Http://www.microbelibrary.org/component/resource/laboratory-test/2869-eosin-methylene-blue-agar-plates-protocol
Typical E.coli colonies are small and pink on EMB agar with a green metallic sheen. It's quite an identifying characteristic, which helps in recognising them.
Green Metallic Sheen. For your info visit this google link: http://www.google.co.in/imgres?imgurl=http://learn.chm.msu.edu/vibl/content/differential/images/eosinmethylene_e.coli.jpg&imgrefurl=http://learn.chm.msu.edu/vibl/content/differential/&usg=__OhC3BdwyGilbg29_r5t1nch-aOE=&h=756&w=800&sz=88&hl=en&start=1&zoom=1&tbnid=dsdb-mM_dE47TM:&tbnh=135&tbnw=143&ei=ftTfUbH6OonJrAfKooFY&prev=/search%3Fq%3Dgreen%2Bmetallic%2Bsheen%2Bof%2BE%2Bcoli%26sa%3DG%26hl%3Den%26site%3Dimghp%26tbm%3Disch&itbs=1&sa=X&ved=0CCwQrQMwAA
Lactose fermentation produces acids, which lower the pH. This encourages dye absorption by the colonies, which are now colored purple-black. use chromogenic medium for selective and identification use colinstant agar.
Eosin methylene blue agar provides a rapid and accurate
method of distinguishing E. coli from other gram-negative , the colour is green metallic sheen
The colour of E coli is green metallic sheen colour on EMB agar
simple method is that set id SIMCUT,90% you can identify E.coli.
Distinctive Green metallic sheen due to the metachromatic properties of the dyes used with agar.
Dear people, isn't it enough to repeat the same answer once?! Nomally you vote the same answer up! Or are you publishing the similar results that you generate in more than one journal? No! Thanks! Cheers, Nadine
E.coli colonies look greenish metallic sheen colour on EMB agar
Saba - that is not typical E. coli colony morphology on EMB, as noted above there's no green metallic sheen. E.coli on EMB really does look like green metallic paint - geenn irridescence on an angle.
It's hard to tell the exact photo from the photo, but if the colonies are purple to blue-black it could be Klebsiella or Enterobacter. You could try streaking onto Standard Methods Agar and growing overnight to get isolates, then using IMViC test or API 20E for confirmation.
i faced a problem in obtaining green metallic sheen on EMB agar using std E.coli culture. does anyone know why E.coli showed no sheen on EMB???
Dear Tejal,
U can increase the quantity of lactose in the media as the bacteria ferment lactose and produce strong-acid. This encourages dye absorption by the colonies.
Hi Tejal,
Only Lactose fermenting E.coli give a green sheen on EMB. Not all E.coli are lactose fermenters.
nonlactose-fermenting gram-negative bacteria appear pink on EMB plate
Quite a late reply, but might be relevant to someone finding this thread on a web search. From what I can gather through online searches, some studies find 10-20% of E.coli isolates are non-lactose fermenters. Some have made the distinction that of this 10-20% some do ferment lactose but slowly, and may require (e.g.) a 48hour incubation as opposed to 24hr for this to be apparent.
I would note that even with textbook colony morphologies on MacConkey Agar and EMB, three recent isolates were tested by API 20E and found to be Enterobacter cloacae. Interestingly the Hygiena Microsnap E.coli method correctly identified these isolates as NOT being E.coli -- based on B-glucuronidase activity basically.
Richard Deschene, I concur with you, particularly on the fact that, some have made the distinction that of this 10-20% of E.coli do ferment lactose but slowly, and may require 48 hours incubation as opposed to 24 hr for this to be apparent.
Additionally insufficient incubation temperature would delay the appearance of typical greenish metallic sheen colonies of E. coli.
the colour of the colonies on the EMB media is complicated. two factors contribute to the dynamics of the colour of a colony.
1. the buffering capacity of the media
2. how much the bacterial colony lower the pH of the media
under normal circumstances, E.coli should produce green colonies with a metallic finish. However, if the media have a different pH or buffering capacity, E.coli may not produce the typical green metallic sheen. you can find more information of colony colour in the following link.
https://sharebiology.com/emb-agar-eosin-methylene-blue-agar/
According from Microbiology book by Mahon, the carbohydrates lactose and sucrose are incorporated to allow differentiation of isolates based on lactose and sucrose fermentation. Fermentation is detected by color changes.
Escherichia coli is a coliform lactose fermenter. It forms blue-black colonies with a metallic greenish sheen.
Escherichia coli can be identified with eosin methylene blue (EMB) agar based on the occurrence of a green-metallic sheen
Escherichia coli appears as large, blue-black colonies, often with a green metallic sheen
The color of E. coli colonies on eosin- methylene blue agar according to Mahon appears blue-black. As a result of rapid production of acid from lactose and sucrose fermentation, it produces green metallic sheen.
By using EMB agar Levine, Escherichia coli appears as large, blue-black colonies, often with a green metallic sheen.
Reference:
Hardy Diagnostic. (n.d.). Retrieved from https://catalog.hardydiagnostics.com/cp_prod/Content/hugo/EMBAgar.htm
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