ok.

Here's an example.

We have a bacteria, escherichia coli for example, resistant to pennicilin and beside it, Enterococcus faecium for example, that is not resistant to pennicilin. Now, can the e.coli give that resistant gene, to e.faecium ??

if its on a transmissible plasmid then yes.

Well there are other modes of horizontal gene transfer, including transduction via phages or natural transformation (though Eschericia and Enterococcusspecies are unable to that).

Resistance gets passed across species all the time by various methods. However, it works best in vaguely similar species, as otherwise the genes might be passed on but ineffective due to structural differences. There's conjugation (bacteria sex, notoriously promiscuous across species), transformation (bacteria assimilating loose DNA), and transduction (transfer via virus). Of course the bacteria might develop a resistance of its own accord as well.

these are all true. but the ecoli could catch out the unwary and make the e fecium appear resistant as the blactamase diffuse into the media. one to watch out for if you are training it is a great way to teach people to not trust their eyes but rely on their knowledge and not over complicate things

This will only be visible on plate. And these typically "clumped" colonies are fairly easy to spot.

thanks for the clear answers everyone (espcially Mr Skeptic, can't be any clearer)