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Microbes and Disease
What Are Microbes?
One of my favourite topics to teach in High School is microbiology. The quintessential piece of biology equipment must be the microscope, and my pupils are always keen to see what can be seen in the world of the very small.
Living things are called organisms, and they all share the same seven life processes. The vast majority of life on our planet (both in terms of mass and number) is very small - so small that we need to use a microscope to see them. These organisms are called micro-organisms, or microbes for short
What is a Fungus?
Fungi Fact File
Fungi are the largest micro-organism. They also show a huge variation in size and shape but all possess a nucleus (some fungal cells have more than one nucleus) and a cell wall made of chitin. Unlike Bacteria, fungi can be multicellular as well as single-celled. This means that fungi can create specialised structures for different purposes. For example, the mushroom is the fruiting body (analogous to a flower) of a fungus, specialised for reproduction.
- Examples: Penicillium, Yeast
- Size:Some can be seen with the naked eye. Most are larger than Bacterial cells
- Shape: Huge variety of morphology and structure
- Reproduction: Huge variety of reproductive strategies, from splitting and budding (seen in different yeasts) to sexual reproduction using spores.
- Food Poisoning
- Whooping Cough
Bacteria Fact File
Bacteria are single-celled organisms that show a huge range of morphology (shape). Being prokaryotes, bacteria do not possess a nucleus - their DNA is naked in the cell cytoplasm. Bacterial cells have a cell wall, but it is very different to the cell wall of plants.
- Examples: Streptococcus, Salmonella
- Size: 1/1000mm
- Shape: Spherical, Rod-shaped, Comma-shaped
- Reproduction: Potentially exponential. Most divide by splitting, so 2 becomes 4, then 8, then 16 and so on.
- Chicken Pox
Virus Fact File
Viruses are the smallest type of microbe. The largest is the mimivirus, which can be seen with a good optical microscope and is almost as large as a bacterium. The usual size of a virus is around one millionth of a millimetre long. This makes most viruses difficult to see even with the most powerful of electron microscopes! Unlike every other living thing on our plant, viruses are not made up of cells and cannot reproduce without being inside another cell. This leads some scientists to question whether a virus is an organism at all. Viruses are made up of a protein coat surrounding genetic material:
- Examples: HIV, Flu
- Size:1/1,000,000 mm
- Shape: All viruses have regular, geometric shapes.
- Reproduction: Viruses can only reproduce inside other cells. When infected, a cell can be forced to create thousands of viruses before rupturing and releasing those viruses to infect more cells.
Fungi, Viruses and BacteriaClick thumbnail to view full-size
How Diseases are Spread
"Coughs and Sneezes Spread Diseases!" Microbes can spread in a huge number of ways, but their inexorable march can be stopped using common sense and good hygiene.
- Air: When you cough or sneeze, a fine spray of watery droplets is ejected at high speed into the air. These droplets can contain microbes; if breathed in by someone else, these microbes can infeect that person. Colds, flu, chickenpox, measles and TB are all spread through the air. Remember to "catch it, kill it, bin it" using tissues, soap and bins.
- Touch: Fungal infections such as athlete's foot and ringworm are spread by direct or indirect contact with humans and animals already infected by the fungus. It is very important to not share towels, bedding or shower mats with someone infected with thrush, athlete's foot or ringworm.
- Cuts: Your skin forms a pretty good barrier to microbes, unless it is broken that is! Your body will form a scab over any cut to reform this protective barrier as quickly as possible. This takes time, however, so you should always clean any wounds with antiseptics before covering them - you wouldn't want to force pathogens into your body now, would you?
- Water: Dirty water transmits many diseases including cholera. Dirty water should be avoided at all costs, or at least boiled several times to make safe.
- Food: Food poisoning is caused by bacteria found in food, usually E. coli. This is not a problem provided that food is thoroughly cooked. Bacteria can grow on food after it is cooked, so ensure food intended for reheating is refrigerated quickly, and reheated thoroughly
- Animals: Most of our infectious diseases originated from animals, and animals still play a major role in the transmission of disease today. Mosquitoes carry yellow fever, and many animals can transmit ringworm.
- Sex: Sexually transmitted infections are on the rise in the West. Syphilis, HIV and gonorrhea are all transmitted through unprotected sex with an infected individual. STIs often have very few symptoms and can cause sterility if not treated quickly.
Remember, microbes can enter the body in a huge number of ways (through the eyes, mouth, nose, ears, genitals, cuts etc) but you can protect yourself using basic hygiene rules!
What are Antibiotics?
How we Fight Infections
Infections are usually seen off by our immune system, but there are one or two things doctors, scientists and even the general public can do in the fight against pathogens.
- Immunizations: A vaccine can protect us from diseases such as measles, mumps, rubella and polio. A vaccine contains the microbes that normally causes a disease but have been treated to stop them causing any symptoms. Your body can then ready it's defences (antibodies etc.) in case of infection by the real thing! This uses a trick from the body called immunity - once you have recovered from a disease, small particles called antibodies stay in your blood stream. This will prevent you from getting the disease again, even if reinfected.
- General Hygiene: coughs and sneezes really do spread diseases. We can all keep the number of infections we get down by washing hands regularly, sneezing into tissues that we then bin, and minimising contact with weakened or ill people - such as patients in hospital.
- Keeping clean and tidy: Hygiene can extend to the home as well. Clean surfaces are with antibacterial sprays and disinfectants. Obviously hand washing comes in again here, particularly after using the toilet. Also, make sure your toilet lid is down before flushing - microbes in your faeces can be thrown into the air during flushing...
- Correct food preparation: Make sure that food is thoroughly cooked, unused food is hygienically and quickly disposed of. If storing food, make sure fridges and freezers are at the correct temperature, and not overfilled. Food blocking the ventilation in a fridge can raise the temperature sufficiently to allow microbial growth in your fridge....gross!
- Antibiotics: Only as a last resort (see the video), antibiotics can assist our immune system in seeing off the more persistent and dangerous infections. Antibiotics can only kill bacteria and have no effect on viruses. This is why you may be prescribed antibiotics for a sore throat (bacterial infection) but not for a cold or flu - DON'T ASK FOR ANTIBIOTICS IF YOU HAVE THE FLU! (They won't make the slightest difference.)
How a Virus Replicates
What is your favourite microbe-produced product?
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Uses of Microbes
My favourite question to ask my pupils at this point is: Are all microbes bad? This usually throws up a response about 'good bacteria' in our gut.
In a simple numbers game, there are more bacterial cells in your body than human cells. You do not spend your entire life at Death's Door, so something else must be going on. Indeed, if you were to wipe out your natural bacterial populations, you would find digesting food much more difficult and would be open to a host of dangerous and deadly diseases. Our natural fauna prevent dangerous pathogens from moving in, help digest our food and keep us healthy.
It is not just in our body where we need microbes - they play important roles in a number of industrial processes:
- Baking: Without the fungus yeast in our bread, it would not rise. The yeast respire aerobically during the baking process, releasing carbon dioxide - this causes the bread to rise.
- Brewing: Beer and Wine are also made using yeast. By removing oxygen in the mixture, yeast start to respire anaerobically (without air). This turns the sugars in the mixture into ethanol - a type of alcohol. This processes is known as fermentation.
- Antibiotics: Penicillin was first discovered by Alexander Fleming in 1928 after he accidentally left out some agar plates over a weekend. He returned to notice that the plates had gone mouldy (after a fungus had landed on the plates) but the bacteria he had been growing had died. The mould that had landed on the plate was Penicilium; this had released penicillin to kill the bacteria. Many of our antibiotics originally came from Fungi
- Insulin: The mass production of insulin is only possible thanks to Bacteria. Scientists have developed a technique to splice a human gene for insulin into bacteria. The bacteria then make insulin, but have no need for it and so excrete it. This turns bacteria into a insulin-making factory
- Waste removal: Many microbes break down the dead bodies of animals and plants. Think of a world where nothing rots or decays - leaves would pile up, dead animals would remain at the sides of roads forever, nutrients would not be recycled for plants to use. We also use microbes at sewage plants and in biodigesters to make electricity.
- Other foods: Cheese, Yoghurt, and Quorn are all made using microbes