Lots of seeds are now being spliced with other genetic material - for instance - tomato seeds are spliced with a fish gene that causes the tomato to resist rot - this gene might also do other things to the plant and fruit - but we don't know.
The sprouts might have been spliced with a chicken gene - maybe for faster growth or to resist certain diseases - maybe this slpced animal gene into the pant caused it to be able to harbor salmonella.