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Skip to 0 minutes and 2 seconds A multitude of microbes. Microbes are organisms that are invisible to the naked eye and clinical microbiology is concerned with the range of germs that cause clinical disease. These infectious microbes include the well known viruses and bacteria but two recent additions to this list are the tiny prions, which are responsible for mad cow disease. Certain fungi can also infect humans, causing diseases like athlete’s foot and thrush, and the microscopic protozoa are notorious for causing killer diseases like malaria and sleeping sickness. Other infectious agents include helminths, or the parasitic worms, and ectoparasites such as head lice, which can just about be seen with the naked eye.

Skip to 0 minutes and 47 seconds Scientists and clinicians classify microbes to allow the correct identification, diagnosis and treatment of the infectious agents that are causing disease. A species is a group of organisms that can reproduce with each other, whereas a genus are sets of closely related, but non interbreeding species. We classify bacteria using a variety of characteristics and this includes whether bacteria can be stained with a dark purple dye, and if so, they’re described as being gram positive, or if they can only be stained with a light red dye ,we describe them as gram negative. Not all bacteria are this easy to stain.

Skip to 1 minute and 36 seconds There are some bacteria, such as the one responsible for tuberculosis, that can’t be stained with either of these dyes and it has to be treated with acid before it can be viewed under a microscope.

Skip to 1 minute and 51 seconds Bacteria come in a wide variety of shapes and sizes. There are the circular cocci and the rod shape bacilli. Some bacteria can be grown in air and we call these aerobic bacteria, whereas others, such as the microbes that in fact deep wounds, need an oxygen-free environment to survive and grow. These are the anaerobes. When bacteria multiply they can form clusters or they can grow in long chains, and some bacteria such as clostridium difficile can form tiny spores that are incredibly difficult to destroy.

Skip to 2 minutes and 28 seconds Now, here’s a picture of Staphylococcus aureus taken under an electron microscope and stained a lovely golden colour to emphasize the fact that these are the aureus, or golden bacteria, but over here you can see that it can also be stained using the dark purple stain, so this is a gram-positive bacterium with a spherical shape. So let’s summarise all that information and pull it together. Staphylococcus aureus is a gram positive cocci. It’s able to survive anaerobically, without oxygen. When it multiplies, it forms clusters. The genus is Staphylococcus and the species is Staphylococcus aureus. Now, luckily for clinicians and scientists, human and bacteria are made from different cells with very different structures.

Skip to 3 minutes and 16 seconds Humans, animals and plant cells are made from eukaryotic cells, whereas bacteria are prokaryotic cells. And it’s the differences between eukaryotic cells and prokaryotic cells that have made antibiotics such useful drugs. Antibiotics leave the eukaryotic human or animal cell unharmed but they are designed to target, harm, or destroy the prokaryotic bacterial cell. Viruses can also cause infections but compared with other microbes such as bacteria they are much simpler infectious agents, and they can only survive if they attack and penetrate deep into bacterial, human, animal or even plant cells. Viruses are completely dependent on the host, quickly multiplying inside the cells before they burst out, in search of new cells to infect.

Skip to 4 minutes and 15 seconds One final important point to note is that viruses are not affected by antibiotics and because of this an infection caused by a virus should not be treated using antibiotics because the antibiotic will not affect the infection caused by the virus.

A multitude of microbes

In this video Laura Bowater explains more about microbes, viruses and bacteria.

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This video is from the free online course:

Using Infection Control to Combat Antimicrobial Resistance

UEA (University of East Anglia)