On the photo you can see some  horrible 'mold' on a mandarin, but in fact it's Penicillum Digitatum (a kind of Penicillin, because yes it's an "old" and natural antibiotic if you extract and purify the good molecules!).  It is possible to take a sample and grow it in Petri dishes. BUT Don't do this and don't use it at home! If you still want to experience this, do not use penicillin afterwards! Here the tests carried out are just used to find natural antibiotics, but not to use them!

The second image is Penicillin under microscope.