BOOSTING IMMUNITY: A STRATEGY FOR HEALTH-PATHOGENS: BACTERIA

These ubiquitous microbes are single-cell organisms which reproduce by dividing into two. Their great talent is as chemical engineers; they take in substances through their cell membranes from the environment and transform them into useful products. Their purpose is to feed so that they may grow and reproduce. The activity of bacteria in fulfilling this basic aim makes all other life possible.

Every part of the planetry biosphere teems with bacteria. Plants depend upon them for their food in the soil, we depend upon plants to oxygenate the air and provide food. Bacteria are continually breaking down and recycling the basic molecular materials necessary 'for life. We may not like to acknowledge it, but our own digestive processes depend upon the activities of colonies of bacteria which live in our gut. They manufacture vitamin K, essential for blood clotting, and make some nutrients available to us that our digestive processes cannot produce. A course of antibiotics, particularly tetracycline, can cause weeks of bowel upset by killing too many of the goodies along with the baddies; things get back to normal when the goodies

re-establish themselves. This illustrates both our open-ended commitment to our shared environment, and our intimate dependence on the talents of bacteria.

Since Louis Pasteur confirmed the existence of the bacterial microsphere, the germ theory of disease and our overreaction to it has been central to our concept of illness. Yet if we were to kill all known germs dead, we would rapidly follow them into extinction. Nevertheless it is true that not everything bacteria do is good, and their occupation of some environments can cause trouble.. If this happens to be inside your body, the wrong bacteria in the wrong place, you may suffer from a bacterial infection. In dealing with bacteria and coexisting with them, understanding becomes crucial and a balanced approach essential.

Problem bacteria tend to pick specific parts of the body to inhabit. Meningococcal bacteria invade the brain, where they can cause meningitis; tubercule bacteria go for the lungs, and cause tuberculosis. Some can cause problems in many sites, such as staphylococci, which cause skin boils, sore throats, blood poisoning, or osteomyelitis if they get into bones.

Like viruses, many bacteria can go into a dormant state where they are highly resistant to unfavourable conditions. Once they find a favourable environment they reproduce rapidly; many can double their population every fifteen minutes. At this rate, one bacterium can become sixteen million in only six hours, and thirty-two million fifteen minutes later. This doubling of numbers in a fixed time is called exponential growth; it is characteristic of many life processes. It explains how particularly virulent bacteria can overwhelm us so quickly. Some victims of the Black Death 'woke well at dawn, to be dead by noon', as one observer noted.

Slightly more sophisticated than bacteria are the life-forms broadly classified as flagellates, protozoa and amoebae. These are all microscopic life-forms and some live parasitically in humans. They cause conditions such as vaginal trichomonas, diarrhoea and malaria. For most practical purposes we may think of them as bacteria.

The fungi which infect our bodies mainly grow on our skin and mucous membranes; they like areas which are frequently damp. Fungi as a whole come in a range of shapes and sizes. We are all familiar with edible mushrooms and poisonous toadstools; some fungi are large, some microscopically small, some invisible and others very colourful. Fungi and moulds are

traditionally associated with death and decay. Although they are plants, fungi have no chlorophyll, the green substance which allows other plants to manufacture food by photosynthesis; because of this fungi live by feeding on ready-made organic matter.

Some of the smaller fungi give us useful products. Penicillin is produced by a mould, as in blue cheese, and the yeast sub-group is active in everything from alcohol to our daily bread. Much fungal activity complements the useful work done by bacteria in recycling waste. It is fungal activity which breaks up fallen leaves and converts them to the fertile fine-textured leaf mould found on forest floors. As we may know to our cost, it is also fungal activity which breaks up dead wood.

Fungi also live parasitically on plants and animals. If you are their chosen diet of ready-made organic matter, you may not feel too enthusiastic about this sort of activity. Fungi feed by excreting an enzyme on to the surface where they are growing; this digests the living matter, which is then absorbed by the fungus. This method of attack, and the immune system's

counter-attack with toxic chemicals, gives you some idea why fungal infections such as athlete's foot and thrush are characteristically itchy.

The last creatures our immune systems tackle are worms. Worms are about halfway up the evolutionary ladder. In essence they are cells which have combined to form one tube inside another. Like bacteria and fungi, most worms live industrious and very useful lives, existing as free-living agents in earth and water. Unfortunately, some exist as parasites in both plants and animals. Those we are concerned with are almost microscopic, and around a hundred species are parasitic in humans. Like bacteria, they can invade almost every organ of the body, and the preferred sites of particular species produce specific disease conditions in much the same way as bacteria produce disease.

Serious worm problems are more common in tropical and sub-tropical regions. In these areas one species, the hookworm, causes untold misery and, indirectly, the deaths of millions. Infected children tend to be both physically and mentally retarded, contributing to the cycle of poverty and deprivation upon which the worm depends. The hookworm problem could be solved very simply by two measures: wearing shoes and digging deep holes to dispose of human excreta. Both measures depend, like most measures which create health, upon minor amounts of money combined with major changes in the attitudes of the potential victims.

Temperate zone worm problems are rarely fatal. The most common are infestations of the digestive tract, which are easily dealt with by poisoning the worms. Those worms which can cause us most damage are those for whom we are accidental hosts. The best known is the trichina worm (Trichinella spiralis) which normally lives in pigs and rats. Humans become infected by eating pork containing the larval stage of the worm. The answer to trichina worms is more simple than to hookworms; make sure all pork is well cooked. Fortunately infections with trichina are fairly rare, as the rat-pig part of their life-cycle has become progressively disrupted.

Those are the four main groups of living organisms with which our immune system deals. In addition, it tackles a wide variety of other foreign bodies which enter our bodies. These are either metabolized (that is, broken down for disposal) or moved to the surface to be expelled or lost with replaceable tissues.

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