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 antibiotic given to the livestock. Since the primary study, there have been many well-documented events showing that antibiotic usage in livestock results in direct influence of antibiotic resistance in humans. Major bacterial infections in humans can be traced back to livestock. The family Enterobacteriaceae includes many opportunistic bacteria, including "E. coli", which are commonly found in livestock. Other bacteria include "Klebsiella" and "Staphylococcus aureus". They cause infections in the urinary tract, digestive system, skin, and bloodstream, and account for a significant portion of antibiotic-resistant bacterial infections. The practice of using antibiotics for growth stimulation is problematic for these reasons: Donald