Micro-organisms and Diseases Click to move on Mike Turner, Mar. 2004

Types of Microbe What we often call germs are in fact micro-organisms such as bacteria, viruses and fungi. They are much too small to be seen with the naked eye. There are millions of types of bacteria, fungi and viruses. Some of them are harmful to us, but many are not. E. coli, a bacterium which lives inside humans. A type of flu virus. Athlete’s foot. Click to move on Mike Turner, Mar. 2004

Bacteria Bacteria are living cells. They are found in most places. They are much larger than viruses. Some bacteria cause diseases, such as food poisoning, but many are harmless. The structure of a bacterium is like this : They do not have a nucleus, but do have a cell wall, cell membrane, and cytoplasm. Bacteria can reproduce quickly, but their reproduction is slowed down at lower temperatures. This is the main reason that food stays fresh longer in a fridge. Click to move on Mike Turner, Mar. 2004

Culturing Bacteria In the laboratory, bacteria can be grown, or cultured, in a Petri dish. The dish contains a culture medium for the bacteria to grow on. This has nutrients for the bacteria to feed on. The culture medium needs to be inoculated with bacteria initially. The bacteria will then reproduce. Click to move on Mike Turner, Mar. 2004

Culturing Bacteria - Safety There are several safety precaution that must be taken when working with micro-organisms : Precaution Reason Use a sterilised Petri dish. No unwanted bacteria already in the dish will grow. Never inoculate from areas of the body that may contain harmful bacteria, eg inside the nose or mouth. There is less chance that harmful bacteria will develop in the culture. Fix lid firmly in place. Bacteria will be unable to escape from or enter the dish. Ensure the edges of the dish are not completely sealed. Oxygen can enter the dish, so anaerobic bacteria (which are often harmful), will not develop. Never store the culture at human body temperature (37 degrees celsius). At body temperature, bacteria that infect humans will grow very quickly. Store the inoculated culture upside down. Any droplets of water than condense inside the container will not fall onto the culture. Click to move on Mike Turner, Mar. 2004

Viruses Viruses are very small, much smaller than bacteria. The SARS virus. (There are 1,000,000 nm in 1 mm) Viruses are very small, much smaller than bacteria. Some scientists do not classify viruses as living organisms. This is because they do not need nutrition (and as they do not eat, they do not excrete). Viruses do not have any of the structures found in normal cells. They have a protein coating rather than a cell membrane. They contain a strand of DNA, and to reproduce they infect a host cell with this DNA. A virus approaches a bacterial cell The virus injects DNA into the cell Click to move on Mike Turner, Mar. 2004

The Effects Of Viruses On Cells The viruses’ DNA then takes over the cell, and makes copies of itself. As this happens in many cells, millions of copies of the virus are made. A cell is attacked by viruses (left). So many copies are produced as the virus reproduces, that eventually the cell bursts open, and the new viruses escape to infect other cells. Click to move on Mike Turner, Mar. 2004

Fungi Yeast, penicillin and athlete’s foot are all members of the fungus family, as are mushrooms. Fungi grow well in warm, moist, dark conditions, such as between the toes! To avoid athlete’s foot, it is important to keep the feet cool and dry. Yeast is a type of fungus that is used in producing bread. It produces carbon dioxide as it respires, which makes the dough rise. Yeast is also used to produce alcohol. An important use of fungi is to produce antibiotics, such as penicillin. Antibiotics are used to treat bacterial infections – they attack and kill bacteria. Click to move on Mike Turner, Mar. 2004

Spreading Disease Diseases can spread in many different ways. These include : Person to person - Bacteria and viruses can pass from person to person by blood, saliva or by being coughed or sneezed into the air. Food borne infection – Food that has not been stored correctly, or has been stored for a longer time than it ought to be, will contain lots of bacteria. Also, if an infected or unclean person prepares food then the infection will pass to the people that eat the food. Water borne infection – When water is not properly treated, it can contain many sources of infection. Airborne infection – Some diseases can spread through the air. A dangerous one is Legionnaire’s disease, which can be spread by badly maintained air conditioning systems. Insect borne infection – Many diseases can be spread by insects, when they bite humans, for example the plague. (Borne means ‘carried by’). Click to move on Mike Turner, Mar. 2004

The Body Fights Back We are surrounded by micro-organisms, many of them harmful. They live around us, on us and in us. Even so, we rarely get ill. The body contains a number of defences that fight off the invaders. When you breathe in through the nose, small hairs inside it act as a filter to trap dust and some micro-organisms. Sticky mucus in the airways also traps many microbes. They are then removed from the body when you cough, sneeze or blow your nose. If you cut yourself, platelets from the blood will clot and form a scab, stopping microbes from entering the body and stopping the blood from leaking out. White blood cells rush to the site to attack the microbes that have entered. The white blood cells surround the micro-organisms and ‘eat’ them. They also produce antibodies – chemicals which weaken or destroy the micro-organisms. White blood cells are carried in the blood, and also in the lymph system. White blood cells travel to the site of a wound. Click to move on Mike Turner, Mar. 2004

A Helping Hand When a person has been infected with a particular microbe, the body can produce the correct antibodies very quickly if that type of microbe attacks again. The person is now immune to that disease. If a person is deliberately given some dead or weak microbes, then the body will learn to produce antibodies to attack that microbe, and so will be immune to that disease in the future. This is called vaccination. We say the person has been immunised against the disease. The dead microbes that are put into the body are called vaccines. This is the bacterium that causes tuberculosis (TB). The BCG injection you have in your upper arm is a vaccination that immunises you against TB. Click to move on Mike Turner, Mar. 2004

Some Definitions Can you match the terms and their definitions? Click the mouse to see the answers. Immune Micro-organism Epidemic Vaccine Antibody A very small organism, such as a bacterium, virus or fungus. A chemical that is produced by white blood cells, which kills or weakens micro-organisms. When a disease spreads very quickly to a lot of people. Safe from a particular disease. A substance containing dead or altered micro-organisms, which is put into the body to give you immunity from a disease in the future. Click to move on Mike Turner, Mar. 2004

Thank you for looking at this work, and good luck in your test. You have now reached the end of the revision presentation for the ‘Micro-organisms and Diseases’ topic. I hope you have found it useful. If you have any ideas to improve this presentation please let Mr. Turner know. Thank you for looking at this work, and good luck in your test. Click to finish Mike Turner, Mar. 2004