When I was at Uni, 40 years ago, I was friends with some of the medical students in my year. Antibiotic resistance was a cause for concern then. It has taken about 80years since Fleming and Florey & Chain discovered and developed the first penicillins for us to squander their legacy. Inappropriate prescribing to humans (eg for viral conditions), and use in farming as a 'growth promoter ' by the dosing of otherwise healthy animals being the major factor of overuse allowing resistance to develop by natural selection. Political inertia in the face of resistance from big pharma and the agri business has meant little or nothing seems to have been done to address the problem. It was raised in the media here in the UK about two years ago and STILL nothing seems to be happening.
As good as any short explanation in layman's terms of agricultural use and it effects on resistance can be found on this website- see Sequoyah's A Special Place, Concord Five, Chapter 4. http://www.awesomedude.com/sequoyahsplace/Stories/ASP/htcon5.htm#Chapter_Four . The patient, has been found unconscious in the slurry pit of a dairy farm.