Competent cell growth on all my plates (multi resistant)

[emadsadeghian]

I have been given a batch of XL1 blue cells. I made them competent using calcium chloride procedure. To test them, i plated them out on agar plate containing: Kanamycin, Tetracyclon, Ampicilin an control. After overnight incubation, there is bacteria colonies in all plates. These colonies are so dense we cant not see them separately.
Since I have kept my original stock of cells before making them competent, I did the same test on the original stack and i saw colonies only on the tetracyclin plates (XL1 Blue is resistant to Tet). This means the procedure of producing the competent cell has somehow made my Ecoli strand a multiresistant strain.
My question is if this is possible and if not why this has happened to my batch?