AP Biology Case Study help?

[kirstie p]

The goal of the lab is to clone a gene from Salmonella bacterium into a plasmid in E. coli bacterium, the gene was cut out of the Salmonella chromosome with a restrictive enzyme, and the plasmid was cut with the same enzyme, and ligase was used to combine the Salmonella gene into the plasmid. Electroportation was used to introduce the plasmid into E coli, and then plated onto plates containinf ampicillin. The next day, instead of a few colonies showing up that were expected, the plate was covered with a "lawn" of cells, as though every single cell had grown.

What could have gone wrong? Which reason is the best possible explanation?

1. Electroportation cannot be used on bacterial cells, it works only on plant cells.
2. A selectin antibiotic which was needed, was left out when making the medium, so cells grew whether the plasmid was present or not.
2. The E.coli were already resistant to the antibiotic.

can anybody explain this/ suggest an answer? thank you.