You mean that resistance might just be in the population?

Granted, this is from a meat industry website, so they're not going to be too critical:

Study finds antibiotic resistance in poultry even when antibiotics were not used

By Alicia Karapetian on 3/8/2007 for Meatingplace.com

A surprising finding by a team of University of Georgia scientists suggests that curbing the use of antibiotics on poultry farms will do little, if anything, to reduce rates of antibiotic-resistant bacteria that have the potential to threaten human health.

Dr. Margie Lee, professor in the UGA College of Veterinary Medicine, and her colleagues have found that chickens raised on antibiotic-free farms, and even those raised under pristine laboratory conditions, have high levels of bacteria that are resistant to common antibiotics. Her findings, published in the March issue of the journal Applied and Environmental Microbiology, suggest that poultry come to the farm harboring resistant bacteria, possibly acquired as they were developing in their eggs.

"The resistances don't necessarily come from antibiotic use in the birds that we eat," Lee said, "so banning antibiotic use on the farm isn't going to help. You have to put in some work before that."

Lee and her team sampled droppings from more than 140,000 birds under four different conditions:

• 1. commercial flocks that had been given antibiotics;
• 2. commercial flocks that had not been given antibiotics;
• 3. flocks raised in a lab that had been given antibiotics;
• 4. flocks raised in a lab that had not been given antibiotics.

The researchers examined levels of antibiotic resistance in normal intestinal bacteria that do not cause human illness and, in a companion study published in May in the same journal, also examined levels of drug-resistant campylobacter bacteria, a common foodborne cause of diarrhea, cramping and abdominal pain.

The meat industry is often blamed for all antibiotic resistance, but that really is rather unfair; it's possible that animals are picking up resistant strains from people who don't think it's necessary to finish their course of antibiotics when their infection clears up. But that's just my bias.