What is the difference between Bacteria and Viruses

We hear a lot lately about Legionnaires’ disease and COVD-19 being similar but are they really.

Well no they are not because Legionnaires’ disease is caused by a living organism known as a bacteria whereas COVID-19 is caused by a Virus which technically is not living. It is thought that viruses exist at the boundary between chemistry and life.

As stated in the Scientific American article “Research by Stanley and others established that a virus consists of nucleic acids (DNA or RNA) enclosed in a protein coat that may also shelter viral proteins involved in infection. By that description, a virus seems more like a chemistry set than an organism. But when a virus enters a cell (called a host after infection), it is far from inactive. It sheds its coat, bares its genes and induces the cell’s own replication machinery to reproduce the intruder’s DNA or RNA and manufacture more viral protein based on the instructions in the viral nucleic acid. The newly created viral bits assemble and, voilà, more virus arises, which also may infect other cells.”

Bacteria, such as Legionella species (of which there are about 60 species currently known) are part of the tree of life known as Prokaryotes, simple single cell organisms which are capable of replicating by themselves.

It is thought that there are five million, trillion, trillion bacteria alive on Earth and put together they weigh more than all the plants and animals combined. Just because you cannot see them doesn’t mean they are not there.

Bacteria are single cell organisms that lack the complex organelles found in Eukaryotes and so are very simple organisms. That being said they are very capable of causing illness and death. The bacteria can come in various shapes such as round or oval (called “cocci”), rod shaped (“bacilli” such as Legionella) and twisting (“spirilla”).

Bacteria grow by dividing into two (binary fission), they can do this every 20 minutes given ideal conditions so one bacterium cell can grow to 70 billion bacterial cells within 12 hours. In other words, they can become uncontrollable very quickly which is why in the case of Legionella you must be vigilant at managing your water system.

Your body is full of good and bad bacteria with something like 80% of the cells in your body being bacterial. So we are all aliens really!

Good bacteria are required to help you live, for example helping you digest the food we eat. Bad bacteria cause illnesses such as Legionnaires’ disease, as well as many other potential harmless and harmful illnesses.

Legionella bacteria infect your lungs and lead to a pneumonia-like illness (Legionnaires’ disease) or a flu like illness (Pontiac Fever).

Viruses are also very common, for example influenza and the common cold are caused by viruses. On average children have 7 colds per year so viruses are more common that you may realise.

Viruses require a host organism to grow, so corona viruses like COVID-19 started of as affecting animals and then crossed to becoming a human viral infection. Viruses multiply by invading the cells of a host where it then makes copies of its DNA or RNA, once fully formed they leave the infected cell to infect other cells so spreading the virus.

The primary role of the virus or virion is to “deliver its DNA or RNA genome into the host cell so that the genome can be expressed (transcribed and translated) by the host cell,” according to “Medical Microbiology.” 

Viruses are much smaller than bacterial cells. For example with a diameter of 220 nanometers, the measles virus is about 8 times smaller than E.coli bacteria. At 45 nm, the hepatitis virus is about 40 times smaller than E.coli.

A picture containing sitting, surface, laying, table

Description automatically generated
This digitally-colorized image shows the H1N1 influenza virus under a transmission electron microscope. In 2009, this virus (then called the swine flu) caused a pandemic, and is thought to have killed 200,000 people worldwide. (Image credit: National Institute of Allergies and Infectious Diseases (NIAID))

The human body has several ways in which it fights off an attack from either bacteria or viruses, these are fever, sneezing, crying and the immune system using macrophages.

A fever increases your body temperature which fights the germs and help white blood cells work better. Sneezing helps expel germs from you nose and crying flushes germs out from your eyes.

Once the bacteria or virus enters your body then a special form of white blood cell known as a macrophage takes over. It tries to engulf the intruder (known as phagocytosis) and then uses chemicals it produces (enzymes) to kill the intruder cells. If all goes well your body will learn from this attack and leave you with an immunity to future attacks.

So, whilst there are some similarities between bacteria and viruses, in that they can cause illness which sometimes looks the same, they are in fact very different things, one alive the other not.

Legionella bacteria are a water borne bacteria and currently it is not thought that COVID-19 is water borne so managing your water systems in a building will help manage Legionella bacteria, it will not help manage COVID-19.

If you want to know how to manage your water systems successfully then contact Collaton Consultancy for more advice via our email:




The Bacteria Book by Steve Mould ISBN 978-0-2414-1578-8


Collaton Consultancy Limited

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