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 prophylaxis 2006 against antibiotics for growth promotion purposes. It was estimated in 2014 that over 80% of the world's antibiotic use was on farms. Coccidiosis in fowl had evolved increased tolerance to the antibiotic feed. The WHO warned in April 2014 that farm use was a contributor to superbugs in humans. The Auditor General of Canada found lack of progress in 2014 on antimicrobial resistance despite three years of government funds that should have been used to implement a reduction programme. A CBC writer was concerned that there was in Canada "no coordinated national system to control antibiotics in agriculture." Due