Antibiotic resistance

Antibiotics are substances that kill or interfere with the growth of micro-organisms, especially bacteria. Examples include penicillin and tetracycline, but there are many more.
They are used to treat, and sometimes to prevent, infection. Apart from paracetamol and aspirin, no other medicines are used so widely.
They are different from most disinfectants, which also kill bacteria, because they do not harm the person taking them. This is called ‘selective toxicity’

Not all micro-organisms are susceptible to all antibiotics. Micro-organisms which are not killed or inhibited by an antibiotic are called “antibiotic resistant”. They continue to grow and multiply in the presence of that antibiotic. Organisms which are resistant to several antibiotics are called “multiresistant”.
There are several ways in which bacteria can be resistant. Some destroy the antibiotic, for example by producing enzymes against it; some prevent the antibiotic getting into their cells; others get the antibiotic out of their cells before it can harm them.

Some bacteria are naturally resistant; new resistances also arise spontaneously by chance mutations and these resistant strains then multiply.
Some resistances can be passed from one bacterium to another, spreading resistance between species. Loops of DNA (called plasmids) carry the resistance genes from one bacterium to another.
When an antibiotic is given, it kills the sensitive bacteria, but any resistant ones can survive and multiply.
The more antibiotics are used (in animals and agriculture as well as in man) the greater will be the “selective pressure”, favouring resistant strains. This is an example of Charles Darwin's Theory of evolution, operating the “survival of the fittest”.
Antibiotics don’t ‘cause’ resistance; rather, they create an environment which favours the growth of resistant variants which already exist in nature or arise by chance.

Once resistance has been established, it can evolve rapidly because bacteria multiply quickly. Overnight, one bacterium can multiply to become a billion. Resistant variants can swiftly over-run a bacterial population.
The resistant bacteria then spread through direct contact with a person or animal with that infection in the same way that other bacteria spread.
Resistance is a particular problem in hospitals and places like old peoples' homes where many vulnerable people are gathered together. (Patients in hospital also often need antibiotics, and intensive use means resistant bacteria are more likely to emerge).
Antibiotic resistance is more common in some countries than others (usually those where use of antibiotics is less strictly controlled). Increased international travel means that individuals infected with resistant microbes in one country can spread them to another country very quickly.
It is thought that the widespread use of antibiotics in animals has led to resistant strains of some bacteria being transmitted to humans through food.

An infection caused by bacteria that are resistant to the antibiotics usually used to treat that infection, may fail to respond to treatment. This can result in a longer illness and sometimes a greater risk of death.
The alternative antibiotics available for treatment may be less effective, or cause more side effects, and are often more expensive. They may also have to be given in much larger doses and by injection rather than by mouth.
One bacterium, which occurs mainly in hospitals, called methicillin-resistant Staphylococcus aureus (MRSA), is resistant to many antibiotics so is harder to treat.
Resistance to widely used antibiotics is also increasingly seen in the bacteria that cause pneumonia, tuberculosis, dysentery and some types of food poisoning.

Antibiotic resistance is to some extent inevitable because we cannot stop using antibiotics. But we can do a lot to slow down its emergence and contain its spread.

We can “keep ahead of the bacteria” by:

Educating doctors and patients to discourage inappropriate prescriptions for antibiotics; most simple coughs, colds, sore throats and influenza are caused by viruses and an antibiotic won&#3

9;t help.
Advising patients, if they are prescribed antibiotics, to complete the course; stopping before the end of a course may make it easier for the resistant bacteria to take over. This is especially important in tuberculosis.
Reducing the use of antibiotics in farm animals, especially where these are used just to enhance their growth.

High standards of sanitation and hygiene, especially in hospitals and old people’s homes, are needed to stop outbreaks of resistant bacteria.

Antibiotic use abroad influences resistance in the UK. International co-operation is needed to minimise the future emergence and spread of antibiotic resistance. In some countries, antibiotics can be bought without a prescription from a doctor, encouraging inappropriate use.
Pharmaceutical companies are placing renewed emphasis on the search for new antibiotics and are also developing new vaccines to prevent common infections.

‘The Path of Least Resistance’ – the report on Antimicrobial Resistance from the Standing Medical Advisory Committee
The Government's Response to the House of Lord's Report “Resistance to Antibiotics and other Antimicrobial Agents”

(Source: HPA)

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