I'm growing some E.coli bacteria on LB medium with ampicillin and I recently observed a blue/green staining of the plates after one night of growth, which starts where the bacteria have grown, and then diffuses to the all plate. I was told it might be some Pseudomonas instead of E coli, but I'm a bit confused as I observed that for 12 different strains (independant, but grown at the same time), and the colonies look very similar to E coli colonies. So I think a contamination of my strains by Pseudomonas is unlikely but who knows..
Has anybody observed anything like that with E coli? Do you think they are actually Pseudomonas? How can I distinguish easily some E coli colonies from Pseudomonas?
I hope somebody could help me as it is very confusing for me....
Thanks a lot!