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Types of Germs

By: Hsin-Yi Cohen BSc, MA, MSt - Updated: 24 Jan 2018 | comments*Discuss
Germs Bacteria Virus Fungi Mould Mildew

One of the main reasons we clean is to control and eradicate “germs” - the disease-causing microorganisms that contaminate our world causing infection and illness. While medical advances have made incredible progress in the battle against these pathogens, the best defence is still good hygiene and regular cleaning, whether it is your house or your teeth. Not only does this help to prevent the spread of infection, it also removes the types of environments that encourage these pathogens to grow in the first place.

Types of Germs

Pathogens fall into 4 main categories – in all cases, when the pathogens invade our bodies, they produce toxins that cause infection and/or inflammation leading to symptoms such as fever, vomiting, diarrhoea, respiratory distress and autoimmune reactions such as rashes. If left untreated, serious, fatal illness can result in some cases.


Perhaps the most familiar “germ”, bacteria are single-celled organisms, which can reproduce extremely quickly; in fact, one bacterium could become one billion (1,000,000,000) bacteria in just 10 hours! This means bacteria can be found living on almost every surface in every climate in the world and a single teaspoon of soil can contains over 1,000,000,000 bacteria.

Not all bacteria are dangerous however – in fact, without bacteria, there would be no dairy products such as cheese and yoghurt, there would be nothing to decompose rubbish and clean up oil spills and we would never have developed some important medicines. We even have “good bacteria” that live in our guts and aid in our digestion.

But pathogenic bacteria can be very dangerous, due to the rapid rate of their population growth, and it is these types that we try to keep at bay with regular, effective cleaning and good hygiene practices. Examples of these include Streptococcus, which causes pneumonia, and Salmonella, which causes severe food poisoning and typhoid fever.


These are simpler than bacteria in structure and usually not even really considered a “living organism” although they possess the same frightening ability to clone themselves and reproduce exponentially. Viruses can only survive by taking over a host cell in another creature and so are constantly looking for other animals to infect and invade.

An invaded cell loses all ability for normal function and is forced to follow the viral instructions to produce viral proteins and create more clones of the invading virus. Once these clones are assembled, the virus forces the host cell to rupture, releasing all the clones to infect other host cells nearby – and thus disease spreads.

Viruses can be particularly deadly and unlike bacterial infections, which can be successfully treated with antibiotics if caught early enough, many viral infections are untreatable and fatal. Infamous examples include HIV (AIDS), Ebola and rabies. Other viral infections cause less serious but chronic or repetitive illness, which can be just as debilitating – examples of these include the common cold and Hepatitis A.

Viruses are especially dangerous as they can linger in many environments for long periods – for example, on a doorknob, which is why effective hand-washing is so important!


Mould and mildew, which plague many bathrooms and other damp areas in your house, also belong to the same group of organisms. While they may not be as dangerous as bacteria and viruses, they can still cause irritation and disease as they colonise substrates (including your skin) and release spores through asexual reproduction.

Fungi usually cause problems when they are breathed in or come into contact with the skin and can result in serious fungal infections. Mould spores inhaled in large numbers can trigger, allergic reactions, asthma attacks, increases susceptibility to colds and flu and causes sinus infections.

The biggest problem with fungi is that they are very difficult to kill without harming the host cells as well – thus, any drugs developed usually only manage to prevent further growth but do not manage to kill off the existing colony.


These are parasites such as amoebas which often spread through moisture and water and cause a range of diseases, from gastro-intestinal infections which lead to diarrhoea, nausea and vomiting and stomach aches to more serious illnesses such as dysentery and malaria.

Regardless of the type, “germs” are usually spread through contact via sweat, blood and saliva and through the air via sneezes, coughs and even breathing. Even just cleaning with simple soap and water can effectively control their growth and preventing grime and dust from collecting will help to prevent the kind of environment that they thrive in.

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