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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!  Bacteria live in the air, in the ground, in water, in and on plant and animals, even on and inside 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 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! 

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.

You can’t avoid bad bacteria altogether but the best way to avoid getting really sick is to make sure you are fit and healthy.  That way, even if you do get sick, you are better prepared for recovery!


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 (‘Article 1’) below for news of a bacterium that woke up and grew after being asleep for 8 million years!


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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