For more than 50 years, microbiologists in the U.S. and Europe have warned against using antibiotics to fatten up farm animal. T

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问题     For more than 50 years, microbiologists in the U.S. and Europe have warned against using antibiotics to fatten up farm animal. The practice, they argue, threatens human health by turning farms into breeding grounds of drug-resistant bacteria. Farmers responded that restricting antibiotics in livestock would devastate the industry and significantly raise costs to consumers. We have empirical data that should resolve this debate. Since 1995, Denmark has enforced progressively tighter rules on the use of antibiotics in raising pigs, poultry and other livestock. In the process, it has shown that it’s possible to protect human health without hurting farmers.
    Farmers in many countries use antibiotics in two key ways: (1) at full strength to treat sick animals and (2) in low doses to fatten meat-producing livestock or to prevent veterinary illnesses. Although even the proper use of antibiotics can inadvertently lead to the spread of drug-resistant bacteria, the habit of using a low or "sub-therapeutic" dose is a formula for disaster: the treatment provides just enough antibiotic to kill some but not all bacteria. The germs that survive are typically those that happen to bear genetic mutations for resisting the antibiotic. They then reproduce and exchange genes with other microbial resisters. Because bacteria are found literally everywhere, resistant strains produced in animals eventually find their way into people as well. You could hardly design a better system for guaranteeing the spread of antibiotic resistance.
    The data from multiple studies over the years support the conclusion that low doses of antibiotics in animals increase the number of drug-resistant microbes in both animals and people. As Joshua M. Scharfstein, a principal deputy commissioner at the Food and Drug Administration, put it, "You actually can trace the specific bacteria around and… find that the resistant strains in humans match the resistant strains in the animals." And this science is what led Denmark to stop sub-therapeutic dosing of chickens, pigs and other farm animals. Although the transition unfolded smoothly in the poultry industry, the average weight of pigs fell in the first year. But after Danish farmers started leaving piglets together with their mothers a few weeks longer to bolster their immune systems naturally, the animals’ weights jumped back up, and the number of pigs per litter increased as well. The lesson is that improving animal husbandry—making sure that stalls and cages are properly cleaned and giving animals more room or time to mature—offsets the initial negative impact of limiting antibiotic use. Today Danish industry reports that productivity is higher than before. Meanwhile, reports of antibiotic resistance in Danish people are mixed, which shows—as if we needed reminding—that there are no quick fixes.
    Of course, the way veterinary antibiotics are used is not the only cause of human drug-resistant infections. Careless use of the drugs in people also contributes to the problem. But agricultural use is still a major contributing factor. Every day brings new evidence that we are in danger of losing effective antibiotic protection against many of the most dangerous bacteria that cause human illness. The technical issues are solvable. Denmark’s example proves that it is possible to cut antibiotic use on farms without triggering financial disaster. In fact, it might provide a competitive advantage. Stronger measures to deprive drug-resistant bacteria of their agricultural breeding grounds simply make scientific, economic and common sense.
What can we learn from Paragraph 2?

选项 A、Use of antibiotics can let bacteria change their genes.
B、Drug-resistant bacteria are typically killed by antibiotics.
C、Antibiotics in animals can enter human bodies as well.
D、Antibiotics are used to prevent the spread of illnesses.

答案A

解析 根据第2段第3和第4句“那些存活下来的病菌,通常发生了能抵抗抗生素的基因突变。然后,这些细菌进行繁殖,并与其他具有抗药性的微生物交换基因”可知,使用抗生素会导致细菌基因突变,故A项正确。B项意为“耐药细菌一般会被抗生素杀死”,根据第2段第2句“这种治疗方法仅让抗生素杀死部分细菌而非全部”可知B项表述不正确,第2段倒数第2句“动物体内产生的耐药菌株最终会进入人类体内”得知,可以进入人类体内的是耐药菌株,而不足C项中的抗生素,故C项错误。D项意为“抗生素用以疾病的扩散”在第二段中没有提及,故排除。
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