Antibiotic antibiotic therapy. The antibiotic treatment may select for bacterial strains with physiologically or genetically enhanced capacity to survive high doses of antibiotics. Under certain conditions, it may result in preferential growth of resistant bacteria, while growth of susceptible bacteria is inhibited by the drug. For example, antibacterial selection for strains having previously acquired antibacterial-resistance genes was demonstrated in 1943 by the Luria–Delbrück experiment. Antibiotics such as penicillin and erythromycin, which used to have a high efficacy against many bacterial species and strains, have become less effective, due to the increased resistance of many bacterial strains. Resistance may take the form
Antibiotic use in livestock in its inaugural 2013 report on antibiotic resistance threats in the United States, the CDC identified resistant non-typhoidal "Salmonella" and "Campylobacter" as "serious threats" and called for improved surveillance and intervention in food production moving forward. There are other bacteria as well, where research is evolving and revealing that bacterial resistance acquired through use in livestock may be contributing to disease in humans. Examples of these include Enterococcus (including "E. coli" 0157) and "Staphylococcus aureus". For foodborne illness from "E. coli", which is still not typically treated with antibiotics because of associated risk of renal failure, increasing rates of antibiotic-resistant