Some of these cells will attack and destroy bacteria directly. These are the T-lymphocytes which are infected by the HIV virus. Other lymphocytes begin to divide creating a group of cells which produce proteins called antibodies.

The antibodies stick to the antigens of different bacterial cells causing them to clump. This makes it easier for other white blood cells to engulf and digest the bacteria.

Some of these antibody-making lymphocytes remain in the blood as ‘memory’ cells. If there is another infection involving the same antigen they rapidly divide and produce antibodies. We have ‘acquired’ immunity after the first infection.

Vaccination uses dead, weakened or part microbes to stimulate the immune system. The body suffers a mild form of the disease but the all important memory cells are produced. If a genuine infection occurs, antibodies will be produced rapidly.

Microbe factfile
For the purposes of the programme we have only considered three groups of microbes: a) bacteria, b) viruses and c) fungi. There are also a number of single-celled organisms that cause disease, eg the malarial parasite plasmodium and several forms of dysentery.

a) Bacteria
Bacteria are the most successful group of organisms on Earth in terms of numbers of individuals and species and the variety of habitats in which they are found.

b) Viruses
Viruses do not fit into the normal classification of living things at all.

c) Fungi
In some ways, fungi are like plants, but they are now classified separately.

Smallpox and the Development of Vaccination
In China, inoculation against smallpox was a common practice by the sixteenth century. By the eighteenth century, methods had been developed to weaken the virus and select the less dangerous of two strains. This was done by taking material from people who had already been inoculated and therefore had a mild form of the disease. The scabs collected were kept at 37^oC for a month, resulting in the destruction of up to 80% of the virus particles. The material was then placed on a cotton plug in the nose so that the virus could be absorbed through the nose.

During the seventeenth century the technique spread west. In the process the technique was modified so that matter was introduced by cutting the skin. In the early eighteenth century European travellers would have met the technique in Turkey. One of these was Lady Mary Wortley Montagu, wife of the British ambassador to Turkey. She had her family inoculated in 1718, at the same time that accounts of the process were being published in London.

Edward Jenner lived in Gloucestershire at the time of a major outbreak of the disease. Inoculation with matter from victims of a mild attack was common practice despite some disastrous results. As a doctor he noted that victims of a mild disease common in milkmaids were not affected by the outbreak. He experimented by inoculating cowpox victims with smallpox but none succumbed to the disease.

In 1796 Jenner performed the now famous experiment on James Phipps, a healthy 8 year old. His innovation was to first inoculate James with cowpox. Once James had contracted the milder disease and recovered, Jenner inoculated him with smallpox matter. Thankfully, James remained healthy.

Although Jenner reported his work to the Royal Society, they considered it too radical for publication. Jenner published privately in 1798 and within a few years the practice was widespread. Jenner coined the term ‘virus’ and in 1803 the new process was named ‘vaccination’ after ‘vaccinia’, the taxonomic name for cowpox.

Preventing the Transmission of Infectious Disease
Infectious diseases are spread by a number of routes, and prevention methods match the route taken. It is impossible to produce an exhaustive list of precautions but this could be a valuable area for student research.

The development of antibiotics and mass vaccination campaigns did not take place until the 1950s. Already the incidence of many common infectious diseases in Europe had fallen dramatically since the 1850s. This was almost certainly due to improved environmental conditions and lifestyle such as:

• improved diets
• access to clean water
• safe disposal of sewage
• uncrowded living conditions
• economic security, and with it, high self-esteem

Antibiotics
Alexander Fleming’s famous chance discovery of Penicillium notatum is a fascinating example of how a chance happening was observed by a researcher with the background to understand its significance. Although Fleming managed to isolate small quantities of penicillin, it was found to be very unstable.

It was not until 1941 that Harold Florey and Ernst Chain managed to extract sufficient quantities of penicillin to treat patients. This was partly because commercial firms were committed to making vaccines. The first patient responded well to treatment but eventually died when the supply of penicillin ran out. Although penicillin was used to treat troops after the Normandy invasion of 1944, mass production did not take place until after the end of the war.

Over four thousand antibiotics have now been isolated. Some ‘broad-spectrum’ antibiotics have been used in animal feeds to increase growth rates. The widespread use of antibiotics has led to the development of resistant strains of bacteria. This occurs when a mutation produces an allele that confers resistance on an individual bacterium. As other individuals succumb to the effects of the antibiotic, the resistant strain multiplies rapidly.

Recent developments in enzyme technology and genetic engineering have allowed the modification of existing antibiotics to overcome resistance. However, this can only bring a temporary respite before new resistant strains arise. Particularly dangerous are multiple resistant strains, which arise when bacteria resistant to different antibiotics exchange genes via plasmids. Plasmids are small rings of bacterial DNA which can leave one bacterium and be taken in by another. In some cases these are proving almost impossible to overcome.

Microbes and Health Poem
Here is the poem used in the programme written by Lemm Sissay.

There’s more microbes on earth than stars in the sky
Yet microbes are invisible to the naked eye.

Microbes travel by air, first class, swim through the sea
On earth first, on earth last, infinite for eternity
They’re the dark dancing diva, the wicked weaver
Of diphtheria, tetanus and scarlet fever.

I’ve got a million, million of them on my skin. Fact.
One hundred million, million in my gastro-intestinal tract.

There’s more microbes on earth than stars in the sky
Yet microbes are invisible to the naked eye.

A weakened body fights day and night. Battle.
Colds and flu in human beings,
Disease ridden cattle. Virus injects and infects,
The body tries to reject it
But by the time you feel it, you’re already infected.
This vile, violent, viral army is already within the ranks,
Invading, persuading, raiding the body’s banks.

There’s more microbes on earth than stars in the sky
Yet microbes are invisible to the naked eye.

If your food has stamped upon it a best before date,
It’s because the producers know that microbes won’t wait.
You’ve seen fruit in the bowl, milk full of mould,
Fungi the fun guy has taken hold.
Yeast is a beast of fungi, producing carbon dioxide,
Making alcohol in beer and dough rise.
If it wasn’t for fungi there’d be no blue cheese.
What a fantastic tapestry the natural world weaves.