Antibiotic resistance.

I get it. Resistant bacteria, which normally have to compete with and get held in check by lots of other relatively benign bacteria, suddenly get a leg up because the broad spectrum AB kills off the competition. Reminds me of a documentary I saw awhile back of a kid - Swiss I think - who was misdiagnosed with ear infections as an infant and given constant streams of antibiotics (by doctors!), and ended up just a couple of years later (after the normal bacteria formation in the digestive tract is complete) with a chronic bacterial deficiency. This resulted in a particular bacterial species - usually present in humans but held in check by other species - flourishing in his gut that produced a biotoxin that affected the kid's brain, making him severely autistic. (It was the mother who did some self-educating and by herself discovered proteins in her son's urine suggesting that particular bacteria as the culprit.) They were able to kill back that particular bacteria and reduce the biotoxin level temporarily with an especially potent antibiotic - and the kid actually began to behave and progress normally - but they couldn't keep him on it because of its (the antibiotic's) extreme virulence, so although the experimental therapy was a "success" while it lasted, the kid had to eventually be returned to his autistic existence. All thought to be because of the misdiagnosed ear infections and antibiotics mistakenly given him as an infant. So very sad, but now thought, if I remember the conclusion correctly, to have contributed significantly to a better understanding of what causes, or at least can cause, autism.

Sorry to bore everybody. But it seems like an object-lesson, even if a special case, in the dangers of misused antibiotics.