As a society we have become almost obsessed with the idea that all bacteria are bad and must be eliminated, both in our bodies and in the home. Adverts for cleaning agents with "antimicrobial properties" bombard us on television.

The end result of all this is that last year, in three geographically different areas, three different patients had a strain of a dangerous bacteria, Staphylococcus aureus, which was resistant to the once reliable antibiotic, vancomycin. Fortunately for these patients, their bacteria responded to other antibiotics, and they were cured. But how long will that last and how have we got ourselves to a situation where once again people are dying of pneumonia and meningitis?

Bacteria: a normal part of life

Bacteria are single-celled organisms, which exist in huge numbers everywhere in our environment. They are on our skin, in our guts and all over our houses, gardens, rivers and countryside. They are a necessary and natural part of our life.

The bacteria in our bodies are commensal organisms, that is, we provide them with the environment they need and they in turn protect us from the few bacterial species which can be dangerous to us. If we destroy our natural bacterial population, then the potentially dangerous bacteria are able to multiply and so cause problems.

No-one is saying that antibiotics are not needed to control bacteria which cause infections. However, even these can also have much broader effects on microbial ecology. They will produce long-lasting changes in the kinds and proportions of bacteria, not only in the treated individual, but in the rest of the environment and in others living close to the treated person. This change in the mix of microbial populations often leads to an increase in bacteria which are resistant to common antibiotics, and problems arise when an infection requires treatment.

A public health nightmare

The increase in bacterial resistance to commonly used antibiotics is spreading throughout the world and, in some cases, is leading to the death of people with diseases which have not killed for the past few decades.

Since the 1940s bacteria which are resistant to antibiotics are becoming increasingly common. An even more worrying trend is the increasing numbers which are becoming resistant to more than one antibiotic ? so-called multi-drug resistance.

Certain strains of at least three bacterial species causing life-threatening diseases are now resistant to every type of antibiotic available. One of these is mycobacterium tuberculosis, which causes TB. The others are enteroccocus faecalis, which can affect many parts of the body, and pseudomonas aeruginosa, causing respiratory disease among others.

What are antibiotics?

Antibiotics are naturally occuring substances, made by living organisms, which inhibit the growth or proliferation of bacteria, or kill them directly. In practice, most antibiotics available now have been altered in the laboratory to improve their effectiveness and to increase the range of bacterial species they affect. Some are completely synthetic such as quinolones and sulphonamides, which technically should be considered under the broader name of antimicrobial.

As part of their action is inhibition of growth of bacteria, antibiotics give the infected person's immune system a chance to destroy the invading bacteria for themselves. The drugs prevent the dangerous bacteria from increasing in numbers by entering their cells and interfering with the production of components used to make new bacterial cells. It is by evolving methods to combat this interference with their ability to multiply, that bacteria develop resistance to antibiotics.

Antibiotic resistance

The two main factors which influence whether a bacteria in a person or community will become insensitive to an antibiotic are the prevalence of resistance genes and the extent of antibiotic use. Resistance genes are those which make the proteins which allow the bacteria to shield itself from an antibiotic's effects.

Antibiotic-resistant strains of bacteria are no more virulent than those which are susceptible to antibiotics. But they are harder to destroy. If they are only slightly insensitive, then larger doses of the antibiotic will suffice, but some are highly resistant and need other drugs altogether.

Some resistance genes work by producing enzymes, which degrade the antibiotic, or chemically modify it to make it inactive. Others allow bacteria to alter or replace molecules which are normally bound by an antibiotic, so preventing the drug from acting within the cell.

If a community has bacteria which do not carry resistance genes to a particular antibiotic, then infection by bacteria specific to that community will be controlled by antibiotic use. If the bacterial flora of the community carries many resistance genes, and drugs to which the bacteria are resistant are used continuously, then resistant bacteria will emerge and multiply.

Resistance genes spread through a bacterial population in a number of ways. They may be inherited from previous bacterial generations. New mutations can arise spontaneously, producing a new resistance gene or strengthening an existing one. Bacteria can also pass resistance genes between themselves.

How do antibiotics promote resistance?

Cells which are highly susceptible to antibiotics will die when treated. However, cells which have some initial resistance, or later acquire it, will survive, particularly if too little of the drug is given. The resistant cells, without competition from the susceptible bacteria, will then multiply. Ultimately the most resistant cells in a group will outcompete all the others when confronted by an antibiotic.

Not only do antibiotics promote resistance in bacteria which are pathogenic (disease causing). They also eliminate non-pathogenic bacteria which would usually keep the pathogenic ones in check. In addition, the resistance genes carried by the pathogenic bacteria will pass into the normal bacterial flora, so increasing the population of resistance bacteria which will be able to pass on the resistance trait.

Cephalosporin antibiotics (eg Zinnat and Ceclor) are widely, and usually inappropriately, used in general practice. This widespread use has made a once harmless intestinal bacterium, enteroccocus faecalis, multiply in the population. E. faecalis is naturally resistant to cephalosporins. In most people the immune system prevents the growth of this bacteria so that it does not cause illness. But in patients whose immunity is compromised, enteroccocus can spread to the heart valves and other organs, causing death.

Long use of the antibiotic vancomycin has also produced reservoirs of E. faecalis which are resistant to vancomycin. Some strains of S. aureus are only susceptible to vancomycin. This vancomycin resistance may spread from E. faecalis to S. aureus, making it incurable.

Two bacteria which only five years ago were not known as pathogens, have emerged as carriers of potentially fatal food borne infections to hospitalised patients ? acinobacter and xanthomonas. This is a direct result of antibiotic use.

Entire families affected by antibiotics

Not only do antibiotics affect the bacterial mix of those using them. They also affect others in the same environment. If one member of a family is using chronic antibiotics to treat acne, then others in the same family have antibiotic-resistant bacteria on their skins. Similarly, heavy use of antibiotics in hospitals, clinics and farms (where antibiotics are added to livestock feed) increases the level of antibiotic resistance in those who work in these settings and even in those living nearby.

The rise in international travel means that antibiotic resistance can spread world-wide. Multi-drug resistant TB has spread to the US this way. A strain of multi-drug resistant streptoccus pneumonia has spread from Spain to Britain, America and South Africa. This bacterium causes pneumonia and meningitis among other diseases.

Causes of this increase in antibiotic resistance

Antibiotic use is out of control.

About 50 percent of all the antibiotics consumed each year are accounted for by human treatment. Of this, maybe only half is appropriate ? that is, used against bacterial infection.

If you are over 40, think back on how often you had antibiotics when you were a child. Now compare the number of times that your grandchildren seem to be on courses of antibiotics. It is an unfortunate fact that there is a perception that antibiotics are needed for every minor cough and cold. It is also an unfortunate fact that busy GPs all too often acquiesce to their patients' misguided requests for antibiotics to treat these viral infections, particularly for their children. This becomes an ever increasing spiral of misuse, with patients asking for antibiotics, doctors giving them, and then the doctors believe that the patient always wants an antibiotic (often they will be happy with an explanation of the viral nature of the illness), and so more and more antibiotics are used ? unnecessarily.

Viruses and antibiotics

A viral illness will not respond to an antibiotic. Colds and flu are caused by viruses. The cough which goes with most colds, and with the flu which is going around at the moment, is also viral. Your child's ear infection is usually viral. By pressuring your GP to give an antibiotic in these situations you are simply adding to the problem of antibiotic resistance. This might mean that one day you or a member of your family will die of pneumonia or meningitis, completely unnecessarily.

In industrial countries antibiotics are only available by prescription. However, even with this apparent safeguard, antibiotics are often used incorrectly. People don't finish the course, or don't take the pills correctly. This means that they fail to get the full therapeutic dose and so cannot eliminate the pathogenic bacteria, encouraging the growth of resistant strains. They also stockpile unused antibiotics and then use these to treat their family and friends inappropriately and, if a bacterial infection is present, inadequately, so further promoting resistance.

In developing countries, antibiotics are available over the counter, leading to less control and more potential for resistance. These poor countries then cannot afford the expensive drugs which may be needed to treat resistant bacteria.

The same antibiotics which are used for human treatment are widely used in animal husbandry and agriculture. More than 40 percent of the antibiotics made in the US are given to farm animals. Some are used to treat infection, but most go into animal feeds to promote growth. This is a particularly dangerous use in terms of the build-up of resistance. Amounts too small to have any effect on infection are fed to these animals for weeks at a time. This is a perfect formula for selecting increasing numbers of resistant bacteria in the treated animals. These resistant bacteria are then passed on to the farm workers, and to people who eat and prepare the meat.

Antibiotics are also sprayed over acres of fruit trees to control bacterial infection in plants. In areas of high concentration, all bacteria will be killed. But residues of the antibiotic sprays may not be sufficient to kill bacteria, so promoting resistant strains. The aerosol spray can also carry to other areas, where it will kill off sensitive bacteria, allowing resistant strains to multiply. People eat fruit and vegetables treated in this way, increasing their own potential to carry resistant bacteria.

How can we stop this?

Obviously we cannot stop all antibiotic use to prevent this inexorable rise of resistant bacteria. But we can use antibiotics more responsibly.

Farmers should be helped to find, and encouraged to use, other methods for promoting growth in livestock. Simple measures such as improved hygiene go a long way towards improving growth in farm animals. There are alternative ways of protecting fruit trees from infection ? planting mixed stands, for example.

Wash all fruit and vegetables thoroughly before use. This will clear off resistant bacteria and possible antibiotic residues.

Do not request antibiotics for simple viral infections. They will do you and your family a lot more harm than good! Seek other methods of dealing with acne. Chronic antibiotic use has a lot of problems.

If you do need an antibiotic, finish the course. Never give medication prescribed for yourself to someone else.

Think twice before buying hand creams, soaps and household products which have antimicrobial agents in them. New research is showing that certain of the bacteria-fighting chemicals which are now used in these products can promote antibiotic resistance. It is not necessary to "kill all known germs"! Our immune systems actually benefit from a bit of dirt now and then.

Doctors can also help, sometimes with very simple measures, such as washing their hands between each patient. Wherever possible, a sample should be taken to identify the bacteria causing an infection, and the antibiotic to which it will respond, before starting treatment.

New research is uncovering both new drugs and ways of rejuvenating those drugs which are already useless against certain bacteria. However, this is time-consuming and costly, and, since all the drugs act in a similar way, novel resistance genes are likely to arise in the future.

An environmental problem

This is an environmental problem, and requires control of antibiotic use on an international scale. Countries world-wide should make a concerted effort to educate people about antibiotic resistance and the impact of misuse of antibiotics.

Bacteria are a normal and vital part of life. Trying to eliminate them will only lead to increases in those few which do cause disease. The same is starting to happen to other microorganisms such as fungi and certain parasites. Consumption of medication to eliminate these, as well as all the antimicrobial household products now available, is leading to similar resistant strains of anti-fungal and anti-parasitic drugs.