Over time, bacteria can become resistant to certain antibiotics. This is an example of natural selection. In a large population of bacteria, there may be some that are not affected by the antibiotic. These survive and reproduce, creating more bacteria that are not affected by the antibiotic.

MRSA

MRSA is methicillin-resistant Staphylococcus aureus. It is very dangerous because it is resistant to most antibiotics. To slow down or stop the development of other strains of resistant bacteria, we should:

• always avoid the unnecessary use of antibiotics
• always complete the full course

Tuberculosis

Tuberculosis, or TB for short, is a disease caused by a bacterium called Mycobacterium tuberculosis. Most people who are infected do not show any symptoms. But about 10 per cent go on to develop serious symptoms including shortness of breath, coughing, fever, and even death.

Infected people without symptoms are usually given a course of one antibiotic. Those who show symptoms need a course of several antibiotics at once. This is to reduce the chance of strains of antibiotic-resistant bacteria emerging. 

The main steps in the development of resistance are:

1. Random changes or mutations occur in the genes of individual bacterial cells.
2. Some mutations protect the bacterial cell from the effects of the antibiotic.
3. Bacteria without the mutation die or cannot reproduce with the antibiotic present.
4. The resistant bacteria are able to reproduce with less competition from normal bacterial strains.

Some bacteria have mutated and become resistant to antibiotics, but new drugs are constantly being developed and tested.

Antibiotics

Antibiotics are substances that kill bacteria or prevent their growth. They do not work against viruses. It is difficult to develop drugs that kill viruses without damaging the body’s tissues.

Penicillin

The first antibiotic, penicillin, was discovered by Alexander Fleming in 1928. He noticed that some bacteria he had left in a petri dish had been killed by naturally occurring penicillium mould.

Since the discovery of penicillin, many other antibiotics have been discovered or developed. Most of those used in medicine have been altered chemically to make them more effective and more safe for humans.

Blind trials

In a blind trial, the volunteers do not know which group they are in. But the researchers do. The problem is the researchers may give away clues to the volunteers without realising it. This is called observer bias. It can make the results unreliable.

Double-blind trials

In a double-blind trial, the volunteers do not know which group they are in, and neither do the researchers, until the end of the trial. This removes the chance of bias and makes the results more reliable. But double-blind trials are more complex to set up.

Placebos

Many doctors do not like giving patients with a disease a placebo. They feel the patient will not benefit from taking a fake drug, and will not get better. They do not think this is fair to the patient.

It is important that the results of clinical trials are not influenced by the expectations of the people involved. So volunteers are put into two groups at random. Checks are done to make sure both groups have a similar gender balance and age range.

There are two main types of clinical trial. In both trials one group of volunteers, called the test group, receives the new drug. Another, the control group, receives the existing drug for that illness. If there is no existing treatment, the control group is given a fake drug that has no effect on the body. This is called a placebo. The researchers look for differences between the experimental group and the control group.

Drugs are substances that cause changes to the body. Some can help the body, others can harm it.

Certain drugs can be extracted from natural sources and their existence has been recognised for a long time. For example, willow bark was used by the ancient Greeks to help cure fevers and pains. It was later discovered that the active ingredient was salicylic acid. This was modified by chemists into the substance we call aspirin, which is less irritating to the stomach than salicylic acid.

Three stages of testing drugs

New medical drugs have to be tested to ensure that they work, and are safe, before they can be prescribed. There are three main stages of testing.

1. The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work.
2. Drugs that pass the first stage are tested on animals. In the UK, new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects.
3. Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check they are safe. The substances are then tested on people with the illness to ensure they are safe and that they work.

Medical drug trials are not without risk. Sometimes severe and unexpected side-effects occur.

Most substances do not pass all of the tests and trials, so drug development is expensive and takes a long time.