Unit 265 Outcome 1

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Unit 265 Causes and spread of infection. Outcome 1 Understand the causes of infection Identify the differences between bacteria, viruses, fungi and parasites. Bacteria are a living organism that is found almost everywhere, in soil, water and even in the human body. Not all bacteria are harmful, and some bacteria that live in your body are helpful. For instance, Lactobacillus acidophilus — a harmless bacterium that resides in your intestines — helps you digest food, destroys some disease-causing organisms and provides nutrients. Many disease-causing bacteria produce toxins — powerful chemicals that damage cells and make you ill. Bacteria can multiply very rapidly if given the right environment. Viruses are much smaller than cells. In fact, viruses can only be seen by electronic microscope. To reproduce, viruses invade cells in your body, hijacking the machinery that makes cells work. Host cells are often eventually destroyed during this process. Viruses are responsible for causing numerous diseases. They can eventually be destroyed by the body’s own immune system, although some may remain dormant inside the infected cell and reactivate later. Antibiotics have no effect on viruses. There are many varieties of fungi, and we eat quite a few of them. Mushrooms are fungi, as is the mould that forms the blue or green veins in some types of cheese. And yeast, another type of fungus, is a necessary ingredient in most types of bread. Other fungi can cause illness. One example is Candida — a yeast that can cause infection. Candida can cause thrush — an infection of the mouth and throat — in infants and in people taking antibiotics or who have an impaired immune system. Fungi are also responsible for skin conditions such as athlete’s foot and ringworm. A parasite is an organism that lives on or inside another organism to the detriment of the host organism. These

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