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Bacteria were among the first forms of life on earth, billions of years ago!  Scientists have found fossils of bacteria that are older than three and a half billion years old, that’s a lot older than humans (see the magazine article attached!)!  A bacterium (a single bacteria) is a very simple form of life, just a single cell, compared to humans who have about a trillion cells (that’s 1 x 1013!!).  Bacteria have different shapes and can look like balls, rods or spirals.  Some, like our friend GI Jake who lives in your gut, have two lobes that look like two ears!  These are the bifido-bacteria.  The word bifido just means ‘split into two’ – you can see from the picture that GI Jake is shaped like a ‘Y’ and has two ears called ‘lobes’ – and bacterium just means a single bacteria!

GI Jake - a bifidobacterium!



No matter what shape they have, all bacteria are basically made the same.  They have a tough cell wall that gives them their shape and protects the bacterium.  Underneath the cell wall, the have a cell membrane that lets nutrients get in and out of the bacterium cell.  A bacteria keeps its genes (these are its instructions on how to be a bacterium, just like our genes are instructions on how to be a human!) just floating around inside it, it the space called the cytoplasm
Some bacteria can move by themselves!  These bacteria have one or many things called flagella that look like little tails that let the bacteria swim from place to place.  If bacteria don’t have flagella, they need water, wind, passing animals or you to spread them around! 

Although they are small, bacteria are very clever and they have learnt to live everywhere!  Bacteria live in the air, in the ground, in water, in and on plant and animals, even on and inside of you!  In the many different places on earth where humans cannot live, you can find bacteria.  They are in the coldest parts of the arctic, the hottest parts of the desserts or the deepest parts of the seas.  Some even manage without oxygen and some can even learn to use oxygen when it is there or live without it when it is not!  Most can hibernate for many years without any ill effects (see ‘Attachment 1’ below for news of a bacterium that woke up and grew after being asleep for 8 million years!)!  For most bacteria however, the temperature and conditions of the average healthy human body is their idea of paradise!

Bacteria are like all living organisms, they need to eat for energy and growth.  But what do bacteria eat?  Well, many bacteria eat starches and sugars which can be found on more or less all organic matter.  For other bacteria their diet is not very different from yours because they live in your mouth or digestive system and eat the food you eat!  Other bacteria eat or dead and decaying matter (they are, along with fungi the ‘decomposers’ of organic matter) and some even eat waste products or dangerous materials like oil.  Basically, there are lots of different bacteria out there and between them they will eat just about anything!

Bacteria can make copies of themselves (multiply) wherever they find the right conditions.  This could be anywhere, including on or inside you!  To make more copies of themselves, most bacteria need; food, light, moisture and nutrients, the usual ingredients that allow them to survive.  However, there are bacteria that can live anywhere so they can multiple anywhere, even without light, oxygen, heat or any of the other things a lot of bacteria need!

Bacteria make copies of themselves using a process called binary fission.  This simply means they split in two and make two identical copies with the same structure, genetic information and capabilities of the original cell.  Bacteria can multiply amazingly fast – as fast as once every 20 minutes!  That means if you have 1 bacterium at 9am on Monday, by noon you will have 512, by 4pm you will have over 2 million and by the time you go to bed (8pm) you will have nearly 9 thousand million!  There are some checks in place that keep bacteria from taking you over altogether! They can begin to run out of space, food and other things they need to stay alive.  The good bacteria that live on and in your body reach a state of equilibrium – a point where they are happy and you are happy because they are doing you good!


The good bacteria

There are lots of bacteria that are very important for all living things on earth!  Bacteria have no problem living inside or on you but how do they help?

There are about seven hundred different types of bacteria living inside your gut right now!  They make lots of copies of themselves, so many that there is no room for any of the bad bacteria to grow!  The good bacteria don’t grow too big because there is only a certain amount of resources, the things like food, space and so on, that they need to grow.  When they reach the limit of the resources, they are in equilibrium with your gut.  Equilibrium is the balance where the bacteria are happy because they have somewhere to live and get their dinner every day and your gut is happy because there aren’t lots of bad bacteria!                     

The bacteria in your gut all work together to keep you healthy by destroying bad bacteria, they slow down cells that are growing out of control and they make vitamins.  Even better than that, they help your to digest your food - they are very busy!  Bacteria help you to take the nutrients from the food you eat and make waste with the leftovers that aren’t any use to you! 

You can tell bacteria are working in your gut because you can sometimes smell the gas they produce.  The gas builds up in your intestines, it is a waste product from the bacteria as the work to digest your food.  When there is too much gas for your intestines, it escapes from your body as flatulence – which is also called a fart!  If you eat certain types of foods, like beans, the bacteria make lots of gas.  The gas gets really smelly though is you eat a lot of processed foods or if you don’t chew your food really well before you swallow it. 

Outside of your body, bacteria like lactic acid and streptococcus bacteria are also very useful in producing food.  Bacteria are used to make dairy products like cheese, yoghurts, sour cream and crème fraîche!  These bacteria are added to milk and they grow and ferment the milk.  The different types of bacteria that are added to make the different types of dairy products give each of them the taste you love!  If you ferment milk with bacteria, the products change and get a little thicker.  This is because the main protein in milk, casein, cannot dissolve in the acid that is produced by the bacteria during the fermentation process.  It is lucky this happens – it would be very difficult to drink the cheese in your sandwich!

Bacteria are used a lot in the making of yoghurt and cheese.  Yoghurt is just fermented milk, made by adding good bacteria that you can find in the ‘natural’ yoghurts in the supermarket, and heating for several hours.  Cheese can be made from the milk of lots of animals, but they all need bacteria to turn the milk into cheese.  The different types of bacteria give the different cheeses their own taste and texture (if they are runny or hard, for example).  Both yoghurt and cheese come in a huge amount of flavours – you’ll definitely fine one that suits you!

If you look closely at the labels of dairy products of yoghurts, you will see that some of them have had probiotics added.  This means that good bacteria are added that, if you eat enough of them, they will be good for your health.  GI Jake is a probiotic – he helps to keep you gut healthy and fight off invaders!

It isn’t only dairy products that can be fermented.  – you can ferment vegetables too using bacteria!  If you add lactic acid bacteria to thin strips of white cabbage, they ferment the cabbage to give sauerkraut (which just means, sour cabbage).  These bacteria are also involved in the pickling of foods like onions, gherkins the production of vinegar and the curing of meats.

Bacteria have lots of other uses other than making sure we don’t get hungry!  Scientists have been using bacteria for a long time to produce medicines like vaccines.  Now they are going even further and they are making bacteria work for humans!  Scientists at the APC are using good bacteria to help to understand ho bacteria work in the gut and how they can be used to fight diseases of the gut.  Find out more at:  http://apc.ucc.ie


Bacteria have learnt to live anywhere so they have learnt to eat whatever is closely by to survive.  For some bacteria their diet is not very different from yours because they live in your mouth or digestive system and eat the food you eat.  There are bacteria out there however who will eat anything!  Bacteria have been found that will eat dangerous or harmful substances, like oil.  These have been used to clean up oil spills but unfortunately they don’t work very quickly so it is still best not to have spills in the first place.  Other bacteria eat anything that is decaying.  This sounds quite nasty but it makes sure that decomposing plants and animals don’t become environmental waste.  Bacteria are also great recyclers – they are the new clean-up crew!

Instead of cleaning up fuel, some bacteria make fuel!  Methane makes up a large part of the natural gas found in the earth.  Methane is made by bacteria that live deep underground and sometimes underwater, wherever there is no oxygen.  Natural gas is used as fuel to keep our homes warm.

So, how do you get some good bacteria?  Well, the easiest way is to eat some!  Look at the labels on foods like yoghurt, dairy drinks and cheeses to see which contain good bacteria the next time you are in the supermarket.  Bacteria are good for you – make them work for you!

The bad bacteria

Bacteria get a lot of bad press because some of them are really bad!  There are plenty of good bacteria but these don’t make the news so often because they just get on with their jobs and don’t cause any trouble.  In fact, without good bacteria we would have a lot of trouble surviving because they manage to keep you safe from a lot of the bad bacteria!  

Although they are small, bacteria are very clever and they have learnt to live everywhere, including inside and on you!  Bacteria get a lot of attention because some of them, a small amount, can make you sick or even kill you!   They can also cause some really annoying illnesses like sore ears, nose, throat and eyes.  Some infections can spread right inside your body and give you more serious diseases such as respiratory infections like pneumonia!

If bacteria get inside you, they have the right conditions to grow - food, moisture, nutrients, whatever they need to allow them to survive.  There are also bacteria that can live even without light, oxygen, heat or any of the other things a lot of bacteria need and these can also grow inside you!  Bacteria make copies of themselves, using binary fission, amazingly fast – as fast as once every 20 minutes!  That means if you have 1 bacterium at 9am on Monday, by noon you will have 512, by 4pm you will have over 2 million and by the time you go to bed (8pm) you will have nearly 9 thousand million! 

The bad bacteria in the environment cause lots of problems – they can cause waste and disease.  If you leave food out in the open, it will begin to rot.  This is because bacteria like tasty food too and will eat the food you have left out and make lots more bacteria in the process!  You have to be very careful to store food correctly because if you eat food that contains bacteria, you will get food poisoning which can make you very ill.  You cannot always tell if your food does contain bacteria – unless of course it smells really bad a looks a little yucky!  Sometimes though things can look less than perfect but they are safe to eat.  If a banana skin has spots or a slice of apple gets a little brown because it was left out in the air, they are still perfectly safe to eat and you won’t get sick.  Good hygiene when you are buying, storing, preparing, cooking and eating food will make sure that you avoid getting bacteria on your food and any small amount that do make it will be killed by making sure you cook your food properly.    

Food can be protected from bacteria by preserving it – you can do this by freezing, drying, pickling or salting it.  These methods of preservation slow down the growth of the bacteria or kill them off altogether.  Remember though that bacteria are really tough and there are so many different types you would have trouble counting them all!  Eventually even food that has been preserved can be invaded by bacteria so remember to check all ‘use by’ dates. 

Your body takes the nutrients from the food you eat and leaves the things it doesn’t want or cannot use behind.  These waste products, your faeces (or poo!) can smell pretty bad.  This smell comes from the bacteria that help you to digest the food you eat - they produce gases like nitrogen, carbon dioxide and methane as they ferment undigested complex carbohydrates in your food.  The smell and build up of gas really depends on what you eat!  Some foods like beans, breads, some vegetables and processed food (a lot of the stuff that comes ‘ready-made’) make sure that lots of gas builds up while others have no effect at all.  You know what happens when there is a build up of gas in your body – it is expelled at great speed and usually with a loud noise from your body!  If you have eaten lots of food that make your faeces smell, this will also make your gas smell really bad.  Also, if you don’t chew your food really well, it can go through your digestive system in large lumps.  This means that nutrients are not absorbed properly and also that bacteria ferment even more – which can cause smells to get worse.


Bacteria cause lots of different types of disease, from sore throats and food poisoning to swelling of the brain and death of nerves in your skin!  There are some common villains that cause these diseases and these are usually put into groups according to what shape the bacterium is:

  • Cocci – these are like little spheres or balls
  • Streptococci cause a lot of sore throats and its cousin, Streptococcus pneumoniae causes the more serious lung infection, pneumonia.  A cocci bacterium also causes Meningitis, an infection that causes the membrane around the brain to swell.  Pneumonia and meningitis can be very serious indeed, although with better medicines today, less people die than did before.
  • Bacilli – these are shaped like rods

There are two very well-know causes of food poisoning – salmonella and Escherichia coli (called E.coli).  Salmonella is usually found in chickens and eggs that have been contaminated and anything that has been made using contaminated chicken or eggs.  E. coli lives in your large intestine and doesn’t do you any harm.  If E. coli gets into other parts of your body though, it can cause a lot of problems.  The most common reason people get sick from E. Coli bacteria is if they drink water or eat food that has been washed in water that has untreated sewage in it.  Sewage contains the waste water from toilets and it is usually processed to make it safe.  The other common reason people get sick from E. Coli poisoning is people not washing their hands after they have been to the toilet (ugh!).  Make sure you always wash your hands after you go to the toilet, before you prepare or eat food!

There are other bacteria that cause more serious diseases – tetanus, botulism and tuberculosis.  Botulism is a nasty type of food poisoning while tetanus makes a toxin that makes muscles go stiff.  Neither of these are very pleasant, but tetanus can be prevented by getting an injection from the doctor when you have a serious cut, especially if you are cut by rusty metal.  Tuberculosis (TB) lives in the lungs and destroys them.  Until medicines were found to treat TB, it caused a lot of people to die. 

The drugs that treat a lot of diseases caused by bacteria are called antibiotics.  There are micro-organisms that defend themselves by making antibiotics that kill other micro-organisms.  Penicillin is the best known antibiotic – it is actually made from a mold!  Penicillin was discovered by the scientist Sir Alexander Fleming in 1928.  He found that mold growing with a colony (a group) of Staphylococcus aureus bacteria was killing them.  It wasn’t long before scientists found out what part of the mold was killing the bacteria and they began to make lots of it and people were able to recover from bacterial infections more easily.  The problem was that bacteria are really very clever.  The more antibiotics that people took, the more the bacteria learnt to get around them so today, there are a lot of bacteria that penicillin used to kill but it cannot kill any more.  The bacteria had adapted to the antibiotic, they are drug-resistant.  New antibiotics are very difficult to find – the best way to make sure that all bacteria don’t become drug-resistant is to:

  • only take antibiotics when you really need them
  • always finish the course of treatment that your doctor gives you, even if you begin to feel better
  • never take antibiotics from someone else or antibiotics that are out of date
  • rememberantibiotics do not work on viruses so there is no point in taking them!  Taking antibiotics when you don’t need them because the can reduce the amount of good bacteria in your body and make you even more likely to get another infection!

Bacteria are also responsible for other nasty things like bad odours in the environment and the decay for food and organic material.  Sometimes it isn’t even the action of the bacteria but a substance called a toxin that it produces that does the damage.  Toxins are produced by some bacteria - the botulinum toxin that causes severe food poisoning is one of them.  This toxin affects the nervous system and can be very dangerous.  Another well known example of a toxin that causes disease is Cholera, which is one of the developing world’s deadliest diseases.  Exposure to toxin from the bacteria Vibrio cholerae in contaminated food and water in the walls of your intestine is very serious and can cause death. 

Bacterial toxins can be helpful though, sometimes they protect you against disease.  The part of the toxin that causes the disease is shut down and a vaccine is made to protect and prevent you from getting the disease.  Some of the diseases above, like cholera and others like diphtheria have vaccines made from their toxins that protect against getting the disease.

Bacteria can live for a very long time so it isn’t clever to think something is safe because it is old!  Most bacteria can in fact hibernate for many years without any problems.  Read the report (‘Attachment 1’) below for news of a bacterium that woke up and grew after being asleep for 8 million years!


The ugly bacteria

The really ugly bacteria are the bacteria that cause the really horrible diseases.  These are usually the ones that are very contagious, they pass from one person to the next, very quickly and very easily.  A lot of the really ugly bacteria are also very serious and they used to kill a lot of people.  Medicine has improved so that less people die now, but these are still not diseases that you would want to get!

The ugly bacteria usually contaminate the air (by coughing and sneezing) or water, things that you need to survive!  Cholera is spread through contaminated drinking water while tuberculosis (TB) and pneumonia are spread by bacteria that are in the air.  There have been lots of cholera and TB epidemics, where lots of people were sick with the same disease at the same time, but modern medicine and better hygiene means that these diseases don’t really happen in developed countries any more. 

A disease that still frightens people is the Bubonic plague (sometimes known as the Black death).  The plague is caused by a bacterium called Yersinia pestis.  It killed millions of people, maybe half of the people living in all of Europe at the time, during the 14th century!  Plague bacteria was carried by the fleas that live on mice and rats.  Mice and rats lived everywhere people did at that time, because there were no proper toilets and people did not understand about hygiene.  When the fleas bit humans, they passed on the bacterium and people got sick.  About 6 out of every 10 people who got the plague died (that’s 60%!).  The plague was also called the ‘black death’ because when people died, their faces turned black.  The Bubonic plague is still around in the world, but it can be treated so it doesn’t spread like it used to.   

Another disease that people were very frightened of is leprosy.  Leprosy is caused by a rod-shaped bacterium called Mycobacterium leprae but it is not very contagious (it doesn’t spread very easily).  This bacterium was discovered in 1873 in Norway and it was the first time a bacterium was seen to cause a disease in humans – before then, people thought that leprosy was caused by a curse!  Leprosy kills nerves so people loose their sense of touch and feeling, they go numb.  Parts of the body get injured and people can go blind, get terrible infections or deformities.  People with leprosy were forced to live separately, away from their friends and families.  They often died without ever seeing them again.  Although leprosy still can’t be cured, it isn’t such a problem now because there are antibiotics that mean people can live normal lives with their families and friends.

A very ugly bacterium that is around and causing problems today is MRSA.  This is methicillin-resistant Staphylococcus aureus and causes an infection that is very difficult to cure.  MRSA is resistant to penicillin, methicillin and many other antibiotics so there are very few defences against it.  It is found in hospitals where people are weak because they are already suffering from other diseases or injuries.  You can help to stop MRSA if you are visiting a hospital by making sure you follow all the rules to stop the spread of the disease – in particular, remember to always wash your hands.

Did you know…?

Bacteria make the holes in Swiss cheese!  There are three types of bacteria used but only two of them make lactic acid as a waste product.  At the end of the cheese-making, the third bacteria eats the lactic acid and makes lots of carbon dioxide gas as its waste product.  This gas makes bubbles that are the holes you see in the finished cheese!


Article 1

New Scientist is one of the worlds leading popular science magazines.

Eight-million-year-old bug is alive and growing 

An 8-million-year-old bacterium that was extracted from the oldest known ice on Earth is now growing in a laboratory, claim researchers.  If confirmed, this means ancient bacteria and viruses will come back to life as ice melts due to global warming. This is nothing to worry about, say experts, because the process has been going on for billions of years and the bugs are unlikely to cause human disease.

Kay Bidle of Rutgers University in New Jersey, US, and his colleagues extracted DNA and bacteria from ice found between 3 and 5 metres beneath the surface of a glacier in the Beacon and Mullins valleys of Antarctica. The ice gets older as it flows down the valleys and the researchers took five samples that were between 100,000 and 8 million years old.  They then attempted to resuscitate the organisms in the oldest and the youngest samples. "We tried to grow them in media, and the young stuff grew really fast. We could plate them and isolate colonies," says Bidle. The cultures grown from organisms found in the 100,000-year-old ice doubled in size every 7 days on average.

Whereas the young ice contained a variety of microorganisms, the researchers found only one type of bacterium in the 8-million-year-old sample. It also grew in the laboratory but much more slowly, doubling only every 70 days.  By examining the average length of DNA fragments found in all the ice samples, the researchers determined that frozen DNA is progressively degraded as time passes. Its half life is 1.1 million years – that is, after 1.1 million years half the original DNA has been degraded.

The researchers believe the DNA is degraded by cosmic rays, which are particularly strong at the poles where the Earth's magnetic field is at its weakest.  Paul Falkowski of Rutgers University, who led the study, describes the ancient bacteria as small round cells that had been in a "suspended state of animation for 8 million years". He says the increasingly rapid flow of glaciers into the ocean as a result of global warming could release new organisms into the sea but he does not believe this is cause for concern because marine bacteria and viruses are typically far less harmful to human health than, for instance, those found on land.

07 August 2007


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