As can be seen in attached images, we have cultured a pure E. coli strain on EMB agar, and the strain have grown over all the inoculated area, but only in certain portions of the plate the microorganism showed tipical green, with metalic shine colonies (turning to black with metalic shine in the final areas where the inoculum was spread). We would like to know if anyone saw something similar ever, and opinions of why this phenomenon occurred.
Enterobacter gives fish eye colonies on EMB.. In some cases E. coli loses the metallic sheen with time when cultures are kept more than 7 days, and the colonies become like fish eyes
The plate show this aspect from the beggining of the culture, from 24 hs on
It happens some times.
Some strain of E.coli have lower ability to ferment lactose, maybe you incubate your isolation for 48h all bacteria show metallic green color.
Dear Alireza, thanks for your answer, but I am afraid that it was not a matter of time, as the plate shown this aspect from the beggining of the culture, at 24 hs, and also after 48 and 72 hs at 37°C.
Dear Ceruti Roberto Julio why this issue is important to you?
I saw this issue before many times, but unfortunately I did not see a reference or paper about this.
In biochemistry test for bacteria we do not have liner result like computer data zero or one.
When you do a test result are between 0 to 100% ability of strains.
Probably your strain have 20% ability to ferment lactose, for example.
You can check your media with a ATCC strain and check your strain with addition lactose in media.
Dear Alireza,
It is not particularly important for us this issue, but it caught our attention. The plate was spread from one single pure colony, that is the reason because we are surprised. There are whole zones that are clear, and others where we could see the tipical aspect of E. coli on EMB medium
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