Bacteria and Viruses - Elementary reader coming soon on Read Listen Learn


Bacteria And VirusesWe learn every day at school that human beings are the kings of the planet. It’s just not true! Really, bacteria and viruses are.

Bacteria and viruses are so small that we need a microscope to see them. Because we can’t see them with the naked eye, we often think that they are the same, but they are as different as rhinoceroses and rats. Another thing we often believe about bacteria is that they are bad for us. In fact, less than 1% of bacteria make us sick and we need some of them so that we can stay alive. But viruses are nearly always dangerous and some can kill us.

There are about one trillion (1,000,000,000,000 or 10¹²) bacteria that live on our skin and, maybe, one hundred quadrillion (10¹⁷) inside our bodies: up our nose, on our hair, inside our teeth, everywhere. There are 10¹⁴ bacteria just in our gut to help us to use the food that we eat (or ‘digest’ food). If we kill all these (but that is impossible), we will die. Of course, not all bacteria are the same. There are four hundred different types in and on our bodies.

Bacteria don’t only live in and on people. They can live everywhere. Twenty or thirty years ago, scientists thought it was impossible for anything to live below 600 metres in the sea because there is no light on the seabed and the pressure is huge. It’s the same as you sitting under fifty 747 planes. But bacteria live eleven kilometres down in the Pacific Ocean. They also live in volcanoes and – we think – on the moonScientists found bacteria in a camera that was on the moon for two years! You cannot kill bacteria by freezing them. If you put bacteria in your freezer, they will sleep and then wake up when you take them out. And they are not choosy about their food: they can eat steel, chicken, sulphuric acid (H2SO4), French fries and radioactive waste.

But that’s not all. Bacteria can not only live in difficult places, they can also live for very long times. We have found bacteria in cans of meat about eighty years old, but that’s nothing for bacteria. It’s like Messi playing football against a primary school team. What about this? In the year 2000, American scientists found bacteria in frozen salt that was 250 million years old. They were sleeping but became active again in a few hours. Bacteria have probably been on this planet for 3.5 billion years.

virus 1Bacteria can also multiply very, very fast. A Belgian scientist thinks that one – only one – bacteria cell can make 280,000 billion new cells in twenty-four hours. That’s 28 X 10¹³. At other times, for example when it’s very cold or there is no food, bacteria can almost close down. Then, some bacteria will make a new cell only once in five hundred years.

When bacteria make new cells, they sometimes make a mutant. This usually dies. But sometimes it makes something useful and then it sends this new thing to other bacteria. In other words, bacteria can share information and develop in new ways. This makes it hard to kill them because they keep changing.

In short, scientists think there could be 100,000,000,000,000 (10¹⁴) tonnes of bacteria in the world today! That means A LOT OF bacteria.

Bacteria are useful to human beings. They make our rubbish decay. With no bacteria, everything will stay the same. But bacteria turn food, trees, dead people and animals and many other things into something different. We can then put this on fields, for example, to make bigger and better vegetables. Other bacteria make oxygen. Bacteria in the sea make 150,000,000,000 (15 X 10¹°) kilograms of oxygen every year. No bacteria, no oxygen.

But some bacteria also sometimes make us sick. Gangrene comes from a type of bacteria and so does tuberculosis (or TB). Every year, two million people die of TB. So, it’s true that only one in a thousand bacteria is dangerous for people, but that’s enough. Bacteria are still the number three killer in the world. We are now looking at some bacteria to see what they do. For example, we know that bacteria in your teeth can give you a heart attack. They may also give you cancer. However, in general, bacteria are good for us.

This is not true of viruses. They are never good for us. They make many serious diseases and lots of colds and flu too. There are about five thousand different viruses in the world and they give us smallpox (that killed 300 million in the twentieth century) and AIDS (which kills two million people every year at the moment). But there are worse diseases than smallpox and AIDS. In the First World War from 1914 to 1918, twenty-one million people died. Spanish flu, a virus, killed the same number in four months in 1919. This disease killed maybe fifty to one hundred million people in three years all over the world. In fact, 80% of American soldiers in the First World War did not die fighting – they died of a flu virus.

virus 2Of course, Spanish flu stopped killing people in the 1920s, nearly one hundred years ago. So, we don’t need to worry. But we now know that the first person to die of AIDS was in England …. in 1959. Only three or four people died and then the virus stopped. Nobody knows why. We also don’t know why it started again in the 1980s and why it has not stopped.

Viruses need to go from one animal to another, between people or, often, between animals and people. They do this in different ways. Everybody knows that you get AIDS from sex and you give someone a cold by coughing or sneezing. This is what happens when you get a cold virus. The virus attacks your body. The white blood cells start to attack the virus. They also start to make more and more white blood cells. This is what makes us feel sick. The body tries to get the virus out – by coughingsneezing, from a runny nose and so on. Other people take in the virus through their mouth, nose, etc., from the air or by kissing or, sometimes, by touching.

So, how do we stop viruses and bacteria? The problem is that we often use antibiotics for both. But this medicine is no good for viruses. The best way to fight viruses is by vaccination. When we are at school, the nurse comes and gives us a piece of sugar with medicine on it or an injection. This can make us a little sick, but only a little. The good news is that we will not get this sickness very badly later and, perhaps, die. Why? It’s because the medicine on the sugar or injection gives us a very small amount of the disease. Our white blood cells start to fight the virus and kill it. But when the virus is finished, the body still remembers the virus and so if it comes again, the body is ready.

bacteria 1Another way to stop serious diseases from viruses is not to live with animals. Many farm animals get sick from viruses that can also travel to people. Smallpox can start in cows and then make people sick, for example. A few years ago, many people died of bird flu – it came from chickens in China. AIDS comes from monkeys in Africa. These days, the virus can go from one country to another, from Asia to America, from Europe to the Middle East very easily and very fast. It travels with us on planes, of course. A virus that is not so dangerous to Chinese people can kill Arabs. This happened in the fifteenth century when people from Spain and Portugal went to South America. They were not sick but the viruses in their bodies killed 90% of South American Indians.

We cannot give vaccinations against bacteria. Here, we need to use antibiotics, like penicillin. This kills bacteria. In fact, it killed bacteria – in the past. These days, it is not so useful. Why? The problem is that doctors give us penicillin for every little problem: colds, serious viruses, bacteria and so on. Farmers even give animals food with penicillin in it to stop them getting sick. Now, you remember that bacteria can change easily and get new information from other bacteriacells. This is also true of viruses. They can then change their DNA so that penicillin and other antibiotics cannot fight them.

We need to use less antibiotic medicine, so that we are ready for new diseases and can fight them when they come … because they are coming!


 This post is from our Elementary collection of non-fiction graded readers...

All images from Wikimedia Commons
By MarcoTolo at en.wikipedia [Public domain], from Wikimedia Commons
By Philippe Le Mercier (Own work) [CC-BY-SA-3.0 (], via Wikimedia Commons
By Thomas Splettstoesser ( (Own work (rendered with Cinema 4D)) [CC-BY-SA-3.0 (], via Wikimedia Commons