考满分 toefl

1 .listen to part of a lecture in a microbiology class.

听一段微生物学课上的讲座。

1 .P: last week, we discussed how the discovery of penicillin in 1928 gave rise to the age of antibiotics. Antibiotics became the medication of choice for treating bacterial infections. Bacteria, as you'll recall, are single celled organisms. How does penicillin stop a bacterium from growing? S: It prevents the bacterium from building its cell wall, the thin barrier that protects the organism. P: Good. We also talked about other antibiotics that work by targeting the proteins that bacteria rely on to reproduce. Bacteria generally have a short lifespan, so if we can prevent their reproduction, the bacteria in an area are soon gone. But increasingly, we're finding bacteria that are resistant to antibiotics, that don't respond to antibiotic treatment.

教授：上周我们讨论了1928年青霉素的发现如何开启了抗生素时代。抗生素成为治疗细菌感染的首选药物。大家记得，细菌是单细胞生物。青霉素是如何阻止细菌生长的呢？ 学生：它能阻止细菌构建细胞壁——那个保护细菌的薄屏障。 教授：很好。我们还谈到其他通过靶向细菌繁殖所需蛋白质起效的抗生素。细菌寿命通常较短，所以如果能阻止其繁殖，该区域的细菌很快就会消失。但越来越多抗生素耐药菌出现，它们对抗生素治疗没有反应。

1 .Now this is a natural phenomenon and not altogether unexpected, and that's because organisms mutate. That is, their genetic structure changes randomly. Sometimes those random changes create traits that help an organism survive. When that happens, the traits tend to get passed on to future generations, so say, a random change in the bacterium allows it to overcome an antibiotic. This new form of the bacteria will reproduce in the presence of the antibiotic, while other bacteria die off. Soon the new resistant form becomes the dominant strain of bacteria in that area. This natural process has been aided to some extent by the overuse of antibiotics. The more we use antibiotics, the more opportunity there is for resistant strains of bacteria to emerge, which is why many doctors are now cautious when prescribing antibiotics.

这种情况是自然现象，并不完全意外，因为生物体会发生突变。也就是说，它们的基因结构会随机改变。有时这些随机变化会产生帮助生物体存活的特性。当这种情况发生时，这些特性往往会遗传给后代。例如，细菌的某个随机突变使其能抵抗某种抗生素。这种新型细菌在抗生素存在时仍能繁殖，而其他细菌则死亡。很快这种耐药菌就成为该区域的主要菌株。这种自然过程在某种程度上因抗生素滥用而加剧。我们使用抗生素越多，耐药菌株出现的机会就越大，这就是现在很多医生开抗生素时都很谨慎的原因。

1 .So how does the resistance to antibiotics work? One of the most successful forms of resistance has to do with enzymes. Enzymes are special proteins that speed up chemical reactions. Bacteria produce enzymes and sometimes genetic mutations cause them to produce new enzymes, including enzymes that attack antibiotic molecules and break them down.

那么抗生素耐药性是如何产生的呢？最成功的耐药形式之一与酶有关。酶是加速化学反应的特定蛋白质。细菌会产生酶，有时基因突变会让它们产生新酶，包括能攻击并分解抗生素分子的酶。

1 .Another form of resistance has to do with bacteria's structure. For example, we saw that penicillin destroys bacteria by destroying their cell walls, but if the chemical structure of the cell wall has changed, then the penicillin may no longer be effective. A third form of resistance involves something called molecular pumps. A molecular pump is a special structure that can transport molecules out of the cell. If an antibiotic enters a bacterium, a mutated pump could send it back outside the cell, preventing the antibiotic from reaching its target.

另一种耐药性与细菌结构有关。例如我们知道青霉素通过破坏细胞壁来杀灭细菌，但如果细胞壁的化学结构改变了，青霉素就可能失效。第三种耐药机制涉及分子泵。分子泵是能将分子运出细胞外的特殊结构。如果抗生素进入细菌，突变的泵会将其排出细胞外，阻碍抗生素到达作用靶点。

1 .So what can be done to overcome these mechanisms of antibiotic resistance? Well, since we know the resistance comes about through genetic changes, we can counteract it through genetically designed antibiotic solutions. For example, researchers have identified the gene in bacteria that prevents penicillin from damaging bacterial cell walls. Most importantly, they found that the gene can be chemically deactivated. In other words, there are chemicals that will stop this new gene from functioning properly.

如何克服这些抗生素耐药机制呢？既然知道耐药性源于基因变化，我们可以通过基因设计的抗生素方案来对抗哦。例如研究人员已发现细菌中阻止青霉素破坏细胞壁的基因。最重要的是，他们发现该基因可被化学灭活。也就是说有些化学物质能阻止这个新基因正常运作。

1 .This opens up an interesting possibility. First, remove the penicillin resistance by turning off the new gene. Then follow that up with penicillin to destroy the bacteria. We might call this combination therapy. One of the benefits of this combination therapy is that we don't have to develop a whole new range of antibiotics after the new gene has been disabled. We can use the same penicillin we've always used.

这开启了有趣的可能性：首先通过关闭新基因消除青霉素耐药性，然后用青霉素消灭细菌。我们可称之为联合疗法。这种疗法的一个优点是，当新基因被禁用后，我们不用开发全新抗生素，可以继续使用原有青霉素。

1 .Some researchers have taken a different approach to finding ways to fight resistant bacteria. They decided to look for an answer in nature, and that's not a bad idea, because nature sometimes comes up with solutions that are far superior to anything we can think of ourselves. For example, the naturally occurring viruses that are called phages. In nature, phages are a type of virus that target and destroy specific bacteria, and because phages already exist, we don't need to spend time and expense to develop them. Phages are also highly adaptable.

如何克服这些抗生素耐药机制呢？既然知道耐药性源于基因变化，我们可以通过基因设计的抗生素方案来对抗哦。例如研究人员已发现细菌中阻止青霉素破坏细胞壁的基因。最重要的是，他们发现该基因可被化学灭活。也就是说有些化学物质能阻止这个新基因正常运作。

1 .As bacteria evolve, so do phages. In theory, this means it should be impossible for bacteria to become totally resistant to phages. But the great challenge with phages is that they're highly specific about which bacteria they target. This means we need to find and catalog a different phage for every different type of bacterium, which is no easy task.

噬菌体适应力也很强，会随细菌进化而进化。理论上这意味着细菌无法完全抵抗噬菌体。但噬菌体的最大挑战在于其高度特异性——这意味着我们需要为每种细菌找到对应的噬菌体，这绝非易事。