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 cover all these areas and instead focuses on the use of antibiotics for growth promotion, which has been banned in Europe since 2006, and on legislation regarding antibiotic use in farm animals in the USA. In 2013, the CDC finalized and released a report detailing antibiotic resistance and classified the top 18 resistant bacterium as either being urgent, serious or concerning threats. Of those organisms, three ("C. diff", carbapanem-resistant enterobacteriaceae, and "Neisseria gonorrhoeae") have been classified as urgent threats and require more monitoring and prevention. In the US alone, more than 2 million people are diagnosed with antibiotic-resistant infections and