Hi everyone. I need to do a lot of colony counting tomorrow and when I was doing it today I’ve noticed that most of the colonies are too transparent - I have to shine bright light on them all the time in order to see something and I might’ve skipped tons of them. I left them for one more night of incubation at 37C and hopefully it gets better, but I am not completely sure about it.

Has anyone ever encountered an issue like this? I’m growing them on LB agar and maybe that’s the reason, but re-plating them is not an option at the moment.

Any tips on light source? Maybe I need to illuminate them with UV to visualise the pigment but I’m afraid of killing them and I know that very specific conditions are required for them to start making pigment.

Thank you!

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