Are microbes good or bad?
With microbes being everywhere you may wonder how scientists can separate them and study them. They do this by using heat and by giving microbes food. From the studies on microbes many things have been discovered. One of the most important was the discovery that a microbe could make a substance which would kill microbes that harm us. This substance we now call an antibiotic. Here is how the first antibiotic was discovered.

When a scientist wants to study the microbes from a place, he or she makes some microbe food. This is a jelly, which is heated to kill any microbes that may be in it, then spread in a shallow dish, which is immediately covered. Inside the dish, the jelly sets and the cover keeps away other microbes from its surface. If a scientist wanted to study the microbes on a piece of bread, for example, he or she would carefully lift up one side of the lid and place the bread on the jelly with forceps which had been heated to kill any microbes on them. The dish of jelly and bread would then be put in an oven and gently warmed. Any microbes on the bread would begin to feed on the jelly and breed. In a few days there would be so many that they would form large colonies that could be seen. For example, some bacteria form waxy spots while fungi, such as moulds, form furry discs. If a scientist wants to separate the microbes, a wire loop is heated to kill any microbes on it then used to scoop up a colony from the jelly. The colony is quickly put into a second dish of jelly and allowed to grow on its own.

One day in 1928, a scientist called Alexander Fleming was clearing away some dishes that he no longer needed. The dishes contained jelly with spots made by bacteria colonies. He noticed that on one of the dishes a mould was growing. This had grown from a spore that had somehow managed to settle on the jelly. When Fleming looked closely at the dish he noticed that around the mould was a clear area of jelly in which colonies of bacteria did not grow. He thought that perhaps there was something from the mould that was entering the jelly and killing the bacteria.

Fleming decided to test his idea and planned and carried out a series of experiments. In his experiments he took a range of bacteria and grew them on separate dishes of jelly. He put a piece of the mould in each dish and left the microbe to feed and breed. When he looked at his dishes again he found that the mould had killed off some of the different kinds of bacteria.

Fleming then realised that a bacteria-killing substance could be useful if he could separate it from the mould. He needed the substance in liquid form and decided to try and grow the mould on a kind of meat soup called a broth. When he tried this the mould grew and he was pleased to find that when he filtered the broth he had discovered that the filtered liquid could kill bacteria.

The mould had been observed and identified long before Fleming's work. In those days, Latin was widely used to help scientists name the living things they discovered. When the mould was observed under the microscope, the scientists thought they could see tiny brushes. These were objects that the mould made to release the spores. The scientists decided to use the Latin word penicillus, which means brush, to name the mould Penicillium. The substance that Fleming extracted from the mould was named penicillin.
Fleming wondered if the penicillin affected living cells.

He thought that if the penicillin killed both bacteria and cells, it would be no use in fighting disease. If, however, penicillin did not kill the cells it could be a useful substance. Fleming set up some more experiments to see what happened when bacteria and white bloods cells were treated with penicillin. To his delight he found that the bacteria died but the white cells lived. He had discovered a way to kill harmful bacteria in the body.

Other scientists became involved in Fleming's work and today there is a wide range of substances produced by microbes to kill harmful germs. These substances are called antibiotics. Their invention was due to the way microbes can be controlled in a laboratory and a scientist who had very keen powers of observation.

Are there any good microbes on the body?
Yes, some on the skin help to keep down the numbers of harmful germs, which settle there. In the intestine there are microbes that make vitamin B for the body to use.

Do other animals have good microbes?
Yes, they do. Some animals, such as cattle, have part of their stomach in the form of a bag, which is full of microbes. When a cow eats it swallows the grass and the microbes feed on it first. In this process they make the grass more edible to the cow. When the cow is resting it regurgitates the microbe-digested grass into its mouth and chews it again. This process is called chewing the cud. The cow then swallows the food for a second time. This time it goes to another part of the digestive system where digestion is completed. You would not enjoy milk or beef if it was not for the good microbes in the cow's stomach.

Do any plants have good microbes?
Yes. Plants such as the pea and clover have good microbes, which come out of the soil and live in their roots. The plant makes swellings on its roots in which they live. The swellings are called nodules. In the root nodules the bacteria take a gas from the air, called nitrogen, and turn it into a food that plants can use.

Are there any good microbes that make food for us?
Yes. Yeast is used to make bread. Bacteria are used in making cheese and yoghurt. Some moulds are used in cheese making. One microbe fungus is used to make a substance that contains the same nutrients as meat but contains less fat and more fibre. It is made to look like meat and can be used instead of meat in making some meals.

Are there good microbes in the countryside?
Yes, there are. If it weren't for them the countryside would be littered with dead plants and animals. These microbes feed on the dead bodies of plants and animals and break them down. In this process, minerals from the bodies are released into the soil. The minerals provide plants with nourishment. So, not only do these microbes clear up the countryside, they help to make the plants grow healthily.

What are bad microbes?
These are the microbes that cause disease in other living things. The disease may affect health for a short time or may be fatal. Bad microbes, such as rusts, affect crops and cause poor harvests. When this happens, people may starve.

Other bad microbes cause food to go rotten or they live in food and cause food poisoning when the food is eaten.

What is a germ?
It is a microbe that causes disease. All viruses cause disease and are germs but only some bacteria are germs. Many are harmless.

Are useful microbes only grown in dishes of jelly?
No. When a microbe is used to produce a large amount of a substance it is grown in a large metal cylinder called a fermenter. It is provided with a liquid food, warmth and all the oxygen it needs. These things encourage the microbe to grow well and produce large amounts of the useful substance. This is then filtered from the microbe and prepared for use by humans.