However, bacteria often contain slight mutations in genetic make-up that allow them to escape death and inhibition. These bacteria, resistant to an antibiotic, can then multiply and quickly become the dominant strain. Just because a bacterial strain only infects chickens doesn't mean antibiotic resistance will remain within the chicken population. Resistance can spread from bacteria that infect livestock to those that infect humans. These tiny organisms often contain small pieces of DNA, called plasmids, that can transfer to other bacteria, with resistance mutations embedded within the plasmid's genetic code.
Many drugs used to treat humans also end up in livestock feed.
Amoxicillin, ampicillin, erythromycin, neomycin, penicillin and tetracycline are among the most common drugs used for treating both people and farm animals. Although many scientists have written articles on the problem of antibiotic resistance in humans and its possible link to antibiotic use in livestock feed, the legal profession has remained relatively silent on the issue, Carol Goforth said. Addressing this subject requires the evaluation of lots of scientific data. At least one government office has attempted to calculate the financial costs of antibiotic resistance. That does not take into account the human suffering and death toll caused by these microscopic marauders, the Goforths contend.