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Martha Ruben, M.D., Ph.D. - Science Kit Martha Ruben, M.D., Ph.D. Dealing with GermsWherever we go, whatever we do, we are surrounded by billions of little beings that we call microorganisms or microbes. They got this name because we can only see them with a microscope, which in some cases has to be very sophisticated and powerful. Microbes cover our skin, mouth, nose, and ears, and even our gut. They form what is called our “normal flora”; we don’t see them, but we need them to stay in good shape. Such wonderful creatures help our skin to keep healthy; they protect our mouth, ears, and lungs from diseases; they even help us to digest some foods and they work very hard in our gut to produce some vitamins we could not obtain otherwise. However, it is not always like that; there are also some “bad germs” that bug us… They are around us, waiting for the occasion to attack and cause disease. One of the functions of the “good microbes” is to protect us from the nasty ones, and, like in any battle, there are many factors that help both parties to fight and the winner to win. For instance, a cut in your skin, the lack of some required vitamins or nutrients, or the invasion of very aggressive germs (like the influenza virus) might favor the development of disease. Alternatively, a strong, well-nourished person will have better chances to avoid getting sick or to recover fast. Many healthy individuals can even carry different agents of disease within their normal flora, without noticing it! Presently, we also have many tools to prevent and fight infections. Vaccines are an example; they are designed to protect us from very crippling or even deadly germs that destroyed young and healthy populations in the past. Some medications, on the other hand, can kill some germs and help for an easy and prompt recovery. The balance between good and evil bugs is very delicate. We already know how to change it to favor our health; however, it if we are not careful enough, we can also distort it and loose control of some nasty germs that are always developing mechanisms to trick us. Related Products: Explore concepts presented in the above article with these Science Kit Products. Prepared Slide, Bacteria, Three Shapes Introductory Bacteria Set, 12 Slides Bacteriology Poster Micro-Slide Viewer back 2 top Germs: Where Are They?The unseen universe of microorganisms is HUGE and DIVERSE. They represent about one half of the biomass (mass of living organisms), while plants constitute about 35% and animals just a 15%. Nevertheless, it takes a great deal of imagination to picture such a world, since we cannot see it; it took many generations of researchers to discover that it exists. At the present time, however, we have many tools that allow us to see or to demonstrate the presence of microbes.A major division in microbiology is between the “living organisms”: bacteria, protozoa, and fungi and “non-living particles”: viruses, viroids, and prions. In the first situation, the microbes possess all the required machinery to make a copy of themselves and to keep growing in number. As for the viruses and viroids, however, this is not possible, and they need a host to reproduce. They are also much smaller and the devices required to detect their presence are much more complicated. The size of protozoa can be measured in micrometers or microns (1 mm = 1000 microns); as an example, the length of a paramecia swimming in the water of your flower vase is about 300-400 microns (close to ½ of a millimetre). Common bacteria, on the other hand, range between 0.5 and 1 micron in diameter. However, viruses are much smaller and need another unit to measure them; they are measured in nanometres (1 micron = 1000 nanometres). Most viruses measure between 20 and 300 nanometres. Nowadays, it is possible to see and even to take a photograph of a virus with a very sophisticated device called electron microscope. Hands-On
2) If the teacher can get an agar plate from a local microbiology lab, the children can touch the surface of the agar with their fingers, or breath at it. Keep the plate on a warm and protected surface for a couple of days. The children will be very excited watching at what grows on it! Macroscopically they will see white or yellowish colonies of bacteria (they appear as little domes). 3) If the teachers can manage to get some stained slides (from the same microbiology lab) they would be able to show some bacteria. There is a basic staining called Gram staining that will give the bacteria a bluish colour (Gram positive bacteria) or pinkish colour (Gram negative bacteria). The bacteria will appear as little rods (bacilli) or spheres (cocci). The cocci may form rows (streptococci) or appear in groups of two (diplococci) or in little bunches (staphylococci). Related Products: Explore concepts presented in the above article with these Science Kit Products. DigiScope 150 & DigiScope 300 Digital Microscopes K-8 Manual for DigiScope Contact Plates: Total Bacteria, Total Coliform, & Yeast/Mold Prepared Bacteriological Medium, Pkg. of 6 Plates Microbiology for Everyone back 2 top Bacteria: What Are They?When we hear the word bacteria, we associate it to nasty organisms that cause diseases or spoil our food. However, most bacteria (from Latin: singular bacterium, plural bacteria) are harmless and they are even beneficial to us. In fact, they play an essential role as decomposers, breaking down organic matter. Along with other microorganisms, the bacteria are natural recyclers; that is, they recover essential raw elements (like Nitrogen, Carbon, Sulphur, and Phosphorus) to keep life going. Without germs, all these vital elements would be locked in dead plants and animals and life would stop because of the lack of ingredients. According to their shapes, the bacteria can be classified as: cocci (singular: coccus) when they look like little spheres, bacilli (singular: bacillus) if they resemble little rods, and spirals. The cocci may appear in groups of two; in larger groups resembling bunches of grapes; or in rows, like beads in a necklace. The bacilli may appear alone or they may also form little necklaces under the microscope. The shape of the bacteria, their ways of grouping together, and their staining properties are very important to identify the different types of bacteria. Many bacteria are used in the industry, and at home, to produce some foods and beverages. Lactobacillus acidophilus is an example; it is used to produce yoghurt and acidic milk. Some bacteria are used to produce all kinds of cheese and other bacterial species produce vinegar, citric acid, and soy sauce. A number of bacteria together with other microorganisms are also used for sewage treatment, to break down solid wastes, and to clean up pollution from water and landfills. A small number of bacteria, however, are pathogens, i.e. they can cause diseases to plants or animals. Some types of bacteria have been identified causing different human diseases, several of them very serious. In the next chapters we are going to take a look at the most common diseases caused by bacteria. We will also talk about ways to prevent some infections, and about some treatments regularly used. Hands-On If yoghurt cultures (Lactobacillus acidophilus and Lactobacillus Bulgaricus) are available, the kids can prepare yoghurt. They have to boil milk (to be sure that no other bacteria are present), wait until the temperature reaches ~ 45 degrees Celsius (the container is still hot, but it can be touched with the hands without scalding), mix with the bacterial cultures, and leave overnight, preferable in a warm, undisturbed surface (it could be at room temperature, in a protected area without cold air flow). Related Products: Explore concepts presented in the above article with these Science Kit Products. Boreal Identification of Bacteria Study Kit Boreal Bacteria Sensitivity Kit - Live Prepared Slide, Cocci in Chains (Streptococci), Stained Insta-Rate Culture Growth Measurement System back 2 top What is a Virus?Viruses are very tiny “particles” that are not considered “living organisms” because they are not able to make copies of themselves without help. That is, they have the genes (which carry all the information necessary) to make new copies identical to the parent, but need to “steal” from their hosts all the tools and functions required to produce new viruses. This is one of the reasons why many viruses can produce very serious diseases; they can stop some host functions and “force” the host to work just for them. Examples of viral diseases affecting humans are: chicken pox, measles, common colds, rabies, and AIDS. Although it was very difficult to demonstrate the existence of these little “particles”, viruses abound in nature, and they infect all living organisms. Different viruses produce all kinds of diseases in plants and animals, and there are viruses that infect even the bacteria! The viruses that infect bacteria are called bacteriophages. In Latin phage means eat, therefore, these viruses are called “bacteria-eaters”. While some viruses may kill the bacteria, in some cases they may help them to resist the antibiotics we are using to cure the infection. And the same happens with humans, while some viruses are able to cause very serious, in some cases deadly diseases; we are able to change some of them “for good” and transform these viruses in harmless particles that will protect us from their nasty parents. These “good viruses” are used to produce vaccines. In most cases either the virus kills the host or the host’s immune system destroys the virus. However, there are viruses that can trick the immune system of the hosts and remain unnoticed for long periods of time. The herpes simplex virus, agent of the cold sores, is a good example. After a first encounter with a host the virus disappears for several months. Nevertheless, they are not gone, they remain in the hosts until their defences decrease because of another disease, sunburn, stress, food poisoning, etc., and then they reappear as a new lesion on the same site as before. It is very difficult to treat infections caused by viruses because they do not respond to antibiotics, used to treat bacteria. In most minor viral infections, the natural defences of a healthy host will be enough to eliminate the invader. However, for severe virus infections the best medication is prevention, i.e. the use of vaccines when they are available, and/or the avoidance of common sources of infection. Related Products: Explore concepts presented in the above article with these Science Kit Products. The Virus, Set of 8 Photomicrographs Virus Modeling, 5 Types Tobacco Mosaic Viral Lab Virus 1-Structure Wall Chart Coliphage Set - Live back 2 top Infections and DiseasesThe multiplication of “bad germs” (medically called “infectious germs”) within the body of the host is called infection. The same term is not used for the multiplication of the normal flora (inoffensive germs that populate our skin, mouth and gut and protect us from the invasion of “bad germs”, see section 1). Not all infections, however, end on diseases; frequently, the host can control the invasion of dangerous germs without becoming sick. The germs that cause diseases are called pathogens (from Latin: pathos suffering, genic producing). Pathogenic bacteria can cause disease by two major mechanisms:
2) Some bacteria mainly multiply and invade the organs of their hosts, and the disease is the result of this invasion plus some toxic products released during the fight of the bacteria with the defences of the host. The invasion of the host’s blood by bacteria is called sepsis, and it can be very dangerous. 3) Most bacteria, use both mechanisms to cause diseases; i.e. they secrete toxins and also invade the organs of the host liberating additional toxins. Viruses, on the other hand, produce diseases by reproducing and creating more viruses (similar to mechanism 2). As will be discussed in Viruses, the invading virus may “force” the host to work mainly in the production of new viruses, and this will distort the normal functioning of the host. Some viruses produce very “acute infections”, that last just a few days, like the winter colds. Other viruses may cause “chronic infections”; that is, the virus stays active, making new viruses and destroying the host’s organs for years (some hepatitis viruses are an example, the viruses may not cure but stay multiplying and destroying the liver of their hosts). A number of viruses can also remain “sleeping” until the host defences are weakened, and then reproduce and invade the host. This situation is called “latency” and it can last for all the life of the host, with alternating episodes of activity and inactivity (example are the cold sores produced by herpes simplex virus). In some case the viruses may take very long time to reproduce and cause disease (called “slow infections”), and some of these “slow virus” can start the development of tumors in the hosts. Several viruses have been associated to the development of some human cancers. Related Products: Explore concepts presented in the above article with these Science Kit Products. Infection: The Board Game Body Defense Against Infection, Set of 8 Photomicrographs Awesome Anatomy Medical Imaging & Diagnosis: You Are The Doctor AccuSTEP Activity Wellness Program Death of an Immune System back 2 top VaccinesThis is the story of one of the greatest human successes over disease: the origin of vaccines. The name vaccine comes from Latin “vaccinus” an adjective from “vacca”, which means cow. In 1798, an extremely alert physician called Jenner noticed that peasants working with cows got infected by a cow’s germ (that produced pustules in the cows’ udders and in the peasants’ hands) and had a mild skin disease. However, at the same time they became resistant to a deadly human disease, smallpox, which also produced pustules all over the body and a serious disease. This observation led Jenner to attempt the inoculation of humans with cowpox extracts to protect them from human pox agents. Jenner’s hypothesis was: if the accidental contamination of the farmers with the cow’s pox agent could protect them from the deadly human disease, a monitored inoculation of the general population with the same germ might protect the whole population from the human disease. And it worked! This was the first successful vaccination ever used, and the reason why this procedure is now called “vaccination” even when the cow’s virus is not used anymore. The eradication of poxviruses was completed in 1979, when the World Health Organization (WHO) certified that the world was free of smallpox. This is the reason why children today do not need to receive this vaccine anymore, even when their parents and grandparents remember receiving it several times, when they were children. Presently, two other crippling diseases: poliomyelitis and measles have been eliminated from a high number of countries, and it is expected that soon they will be completely removed from the world. Following the success with poxvirus vaccines, and after the discovery of several agents that cause severe infectious diseases in humans and animals, a whole collection of vaccines has been developed to prevent such infections in susceptible hosts. We will cover them when we learn about the specific diseases. Related Products: Explore concepts presented in the above article with these Science Kit Products. Rising Threat of Infectious Disease Video Bacteria Video Identification of Bacteria using a Dichotomous Key Theta Technologies Thetacoccus: A Simulated Bacterial Culture back 2 top |
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