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 common foods harboring these pathogens. There is evidence that a large proportion of resistant "E. coli" isolates causing blood stream infections in people are from livestock produced as food. When manure from antibiotic-fed swine is used as fertilizer elsewhere, the manure may be contaminated with bacteria which can infect humans. Studies have also shown that direct contact with livestock can lead to the spread of antibiotic-resistant bacteria from animals to humans. Sampling of retail meats such as turkey, chicken, pork and beef consistently show high levels of Enterobacteriaceae. Rates of resistant bacteria in these meats are high as well. Sources