> I don't follow your logic here, Pete. 

Let me put it differently. Imagine if terramycin was only used as a preventative and all active cases were destroyed, as was recommended by most researchers. It seems to me that terramycin would have retained its effectiveness far longer than it did given the alternative scenario, where it was used to treat active infections. 

The old school proposes that resistant strains are always present and the use of antibiotics selects for them. However, there is an alternate hypothesis, that the organism *responds* to antibiotics by becoming resistant. In this case, if there is no infection, there is no response. Only by exposing active bacteria to the antibiotic would resistance then develop over time.

But, as they stated in the article that I cited, "It is a complex issue that should not be oversimplified or over-generalized because there is not a simple, direct relationship between antimicrobial drug use and antimicrobial resistance." 

I understand the logic which suggests that chronic use of low levels of antibiotics may lead to resistance, but it doesn't mesh with what I have actually observed. Inspecting in New York State, I learned that resistant foulbrood is relatively rare in our area and seemed to originate from one outfit which was notorious for not eliminating foulbrood hives, but dosing them instead. Another large scale outfit that I know of used extender patties during the active season and had no breakdowns as a result. One medium sized operation eliminated outbreaks by regular use of tylosin. Whether tylosin resistance will crop up is another matter. Dunno.

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