nitrogen as a stereocenter in Beta-lactam-antibiotics

Hello,

first of all I would like to apologize if my english isn't perfect. It's not my first language and I am still struggling with some scientific terms. However, I don't find much chemistry forums in my language and I usually have lots of questions, so why not go international with them? :)

I read that nitrogen can be a stereocenter if it is "fixed/locked" in a certain way. Usually this is the case for quarternary amines. However I also read that the N-1 nitrogen, the one "inside" the lactam structure of beta-lactam-antibiotics can be seen as "sort of" a stereocentre. I barely find information about this. Is there a clear answer? Or can we just say that the nitrogen inversion is reduced, but not to what extent/whether there is a stereocenter or not?

Thanks for your answers in advance!

Aconitin