In a quick answer to your first point about the reduction in the beneficial effect to growth and feed efficiency with growth promoters, it's pretty well documented now that there has been a reduction from about 5% to 10% down to about 2%.
We don't really know for sure why that is. It's thought to be in part because we now have better production systems. We have better animal management. We have better biosecurity. We have better systems to prevent the spread of disease in animal populations. We have better quality feed and better feeding regimens. All of those things, plus the emergence of resistance, may also diminish the effectiveness of these growth promoters.
The second question—which, with all of my talking, I've kind of forgotten—is whether people are getting resistant to these. It's the bacteria that are getting resistant; bacteria in people, animals, and in the environment.