Disk diffusion test.... - control problem (Jan/17/2011 )

Recently I was doing disk diffusion test with self made ampicillin disk.

Inhibition zone were forming in all the test strains except my control, e.coli ATCC 25922 (i suppose)

what is the problem I'm facing? Is it the problem of my control strain?

Hola, Yes your control strain is ampicillin resistent. It carries beta lactamase (penicillinase) and destroy all beta lactam antibiotics. For that I think, is the control strain I suposse. Buena suerte

do you know the difference between a positive control and negative control badguy?

The positive one: should be able to survive the antibioticum , the nevative one should die for sure..