Drugs and Antibiotics
IGCSE Biology Topic 15 4:37 English narration · English + 中文 subtitles burned in
Chapters
Transcript
Ask a doctor for antibiotics when you have a cold and they will say no.
感冒时向医生要抗生素，医生会说不。
Not because they are being difficult — because it genuinely would not work, and because taking them anyway makes things worse for everybody.
不是因为医生故意为难—— 而是因为它真的不会起作用，而且照吃不误会让所有人的处境变得更糟。
This short topic explains both halves of that answer.
这个简短的专题解释了这个答案的两个部分。
Welcome to drugs and antibiotics.
欢迎来到药物与抗生素。
What a drug is, what antibiotics do, and how resistance spreads.
什么是药物、抗生素做什么，以及耐药性如何扩散。
Let's begin.
让我们开始吧。
Start with the definition, and notice how broad it is.
先看定义，注意它有多宽泛。
A drug is any substance taken into the body that changes or affects the chemical reactions in the body.
药物是任何摄入体内、 能改变或影响体内化学反应的物质。
That definition is much wider than you might expect.
这个定义比你想的要宽泛得多。
It does not only mean illegal drugs.
它并不只是指非法药物。
Caffeine is a drug.
咖啡因是药物。
Nicotine is a drug.
尼古丁是药物。
Alcohol is a drug.
酒精是药物。
And so is every medicine on a pharmacy shelf.
药房货架上的每一种药也都是。
Many drugs are medicines that help to treat illness — and antibiotics are one of the most important kinds.
许多药物是用来治疗疾病的药品—— 抗生素就是其中最重要的一类。
Antibiotics are drugs used to treat bacterial infections.
抗生素是用来治疗细菌感染的药物。
They kill bacteria, or stop them growing.
它们杀死细菌，或者阻止细菌生长。
But here is the sentence that carries the marks: they do not affect viruses.
但这句话才是得分的关键：它们对病毒没有作用。
Not weakly — not at all.
不是作用弱——是完全没有作用。
Bacteria and viruses are completely different kinds of thing, and antibiotics only work on bacteria.
细菌和病毒是完全不同的东西，抗生素只对细菌起作用。
So antibiotics cannot cure a cold, and they cannot cure the flu, because both of those are caused by viruses.
所以抗生素治不好感冒，也治不好流感，因为这两者都是病毒引起的。
That is why the doctor says no.
这就是医生说不的原因。
How do you find out which antibiotic works best against a particular bacterium?
你怎么找出哪种抗生素对某种特定细菌最有效？
There is a standard practical.
有一个标准实验。
Small paper discs, each soaked in a different antibiotic, are placed on a plate covered with a lawn of those bacteria.
把小纸片分别浸泡在不同的抗生素里，放在长满那种细菌的培养皿上。
Then you leave it to grow.
然后让它生长。
Where an antibiotic kills the bacteria, a clear ring with no growth appears around the disc.
凡是抗生素杀死细菌的地方，纸片周围就会出现一个没有细菌生长的透明圈。
And here is how you read it: a bigger ring means the antibiotic is more effective, because it killed bacteria further away from the disc.
读法是这样的：圈越大表示这种抗生素越有效，因为它杀死了离纸片更远的细菌。
Watch what happens to a population when something kills most of it.
看看当某种东西杀死一个种群的大部分个体时会发生什么。
The few survivors are not random — they are the ones that could already survive.
少数幸存者不是随机的——它们是本来就能活下来的那些。
Some bacteria are resistant to an antibiotic — meaning that antibiotic no longer kills them.
有些细菌对某种抗生素有耐药性——意思是那种抗生素不再能杀死它们。
Now follow what happens in three stages.
现在跟着看三个阶段发生了什么。
Stage one: in any large population a few bacteria are already resistant, purely by chance.
第一阶段：在任何大的种群里， 纯粹出于偶然，已经有少数细菌是耐药的。
Stage two: you give the antibiotic, and it kills the non-resistant ones — so only the resistant few survive and multiply.
第二阶段：你使用抗生素，它杀死了不耐药的那些——所以只有耐药的少数存活并繁殖。
Stage three: those survivors become most of the population, and now the antibiotic barely works at all.
第三阶段：这些幸存者成为种群的大多数，现在抗生素几乎完全不起作用了。
That is why the antibiotic slowly becomes less effective for everyone, not just for one patient.
这就是为什么抗生素会慢慢地对所有人都变得不那么有效，而不只是对一个病人。
Here is the exam question, and it has one trap in it.
这是考题，里面有一个陷阱。
A patient stops taking their antibiotic as soon as they feel better, and the infection comes back worse.
一个病人一感觉好转就停了抗生素， 结果感染复发而且更严重。
Explain that using resistance.
用耐药性来解释。
In the starting population a few bacteria were already resistant, by chance.
在最初的种群里，出于偶然，已经有少数细菌是耐药的。
The antibiotic killed the non-resistant ones, so those few survived, multiplied, and came to make up most of the population — and now the antibiotic no longer works on it.
抗生素杀死了不耐药的那些，所以这少数存活下来、繁殖，并成为种群的大多数—— 现在抗生素对它不起作用了。
Stopping early leaves behind exactly the bacteria that are hardest to kill.
提前停药留下的正是最难杀死的那些细菌。
Now the trap: you must say the resistant bacteria already existed and survived.
现在说陷阱：你必须说耐药细菌本来就已经存在并且存活下来。
Writing that the antibiotic made them resistant is wrong, and it loses every mark.
写抗生素"让它们变得耐药"是错的，会丢掉全部的分。
For the supplement paper, how do we slow this down?
补充部分：我们怎样减缓这个过程？
Two rules.
两条规则。
First, antibiotics should be used only when they are really needed — not for a cold, not just in case.
第一，只在真正需要时才使用抗生素——不用于感冒，也不要"以防万一"地吃。
Second, always finish the full course, even after you feel better, so that no partly-resistant survivors are left behind.
第二，永远要吃完整个疗程，即使你已经感觉好了， 这样就不会留下部分耐药的幸存者。
Using antibiotics too often lets resistant bacteria spread, and the one you are expected to name is MRSA.
抗生素用得太频繁会让耐药细菌扩散， 你需要能说出名字的那一种是MRSA。
Three marks to lock in.
锁住三个分。
First: a drug is any substance that changes the body's chemical reactions — not only illegal drugs.
第一：药物是任何改变身体化学反应的物质——不只是非法药物。
Second: antibiotics kill bacteria only; they do nothing to viruses, so they are useless against colds and flu.
第二：抗生素只杀死细菌；它们对病毒毫无作用，所以对感冒和流感没用。
Third: the resistant bacteria already existed — the antibiotic selected them, it did not create them.
第三：耐药细菌本来就已经存在——抗生素是筛选了它们，而不是制造了它们。
Master these, and this topic is yours.
掌握这些，这个专题就是你的了。