What are your results?

Colonies are yellow spots large enough that I cannot conclude if it is a single colony for the higher amount of colonies. So I made my serial dilutions to reach from 1000cfu to 3-5cfu. But now at the second day I don't see any colonies. Any clue why?

Description doesn't fit 0157.

0157 should be +/- colorless and not large yellow spots - colonies.

Are you sure of your inoculum?

Yes! I perform colony PCR and everything result positive.

what primers or ID system?

As you see, this growth is not consistent with any E. coli. I'd Gram stain of yellow colony and streak traditional MacConkey and EMB from the original.

And please be careful with your aseptic technique.

I perform colony PCR with Eurofins BacGene E.Coli O157-H7. So from 100cfu/10mL stock I just inoculate to MacConkey plates 330ul to each petri. Total 3 Petri-dishes, total volume inoculation about 1mL. So, how many days are necessary for incubation at 37?

Thank you in advance,

Kiriakos

should be 18-24 hours. Eurofins test confirms presence of 0157 genetic signal. It does not confirm a pure culture or of necessity a viable population of E. coli. You clearly have a colony morphology inconsistent with E. coli and colony count inconsistent with the claim.

Streak for isolation - not dilution plating.