Animal -> bacterial gene transfer seems easier than bacteria -> animal (rotifers are an interesting exception); there are bacteria live in close contact to us but our germ-line cells are protected. Given enough time, even free-living bacteria would start to pick up some of our genes (once the introns were lost).
Is this true? If so, do we see animal/plant genes gradually spreading into single cell organisms as time goes on (although "seeing" this would be difficult)? Is this effect "significant" for evolution in microbes?