Difference Between Bacteria And Viruses

Many people think that both bacteria and viruses are germs that are harmful to human beings. Furthermore, they think that viruses and bacteria belong to the same category that causes infections to us.

However, it is a wrong perception. Bacteria and viruses are two very different infectious agents, and it is extremely important for us to know their features to be able to ward off infections and to remain healthy.

This article explains the features of both as well as the difference between bacteria and viruses to make us better prepared in every sense of the word.

Difference Between Bacteria and Viruses

Bacteria Vs Viruses

On a biological level, the main difference is that bacteria are free-living cells that can live inside or outside a body, while viruses are a non-living collection of molecules that need a host to survive.

Living or Not

Viruses are not living organisms, bacteria are. Viruses only grow and reproduce inside of the host cells they infect. When found outside of these living cells, viruses are dormant.

Their “life” therefore requires the hijacking of the biochemical activities of a living cell. Bacteria, on the other hand, are living organisms that consist of a single cell that can generate energy, make its own food, move, and reproduce (typically by binary fission).

This allows bacteria to live in many places soil, water, plants, and the human body and serve many purposes.

They serve many vital roles in nature by decomposing organic matter (maybe not that vital to anyone who’s forgotten leftovers in the back of the fridge) and by converting nitrogen, through nitrogen fixation, to chemicals usable by plants. Bacteria even know how to work as a team through something called quorum sensing.


Bacteria are giants when compared to viruses. The smallest bacteria are about 0.4 µ (one-millionth of a meter) in diameter while viruses range in size from 0.02 to 0.25 µ.

This makes most viruses submicroscopic, unable to be seen in an ordinary light microscope. They are typically studied with an electron microscope.

Mode of Infection

Their mode of infection is different. Because of their distinct biochemistry, it should come as no surprise that bacteria and viruses differ in how they cause infection.

Viruses infect a host cell and then multiply by the thousands, leaving the host cell and infecting other cells of the body. A viral infection will therefore be systemic, spreading throughout the body. Systemic diseases caused by viral infection include influenza, measles, polio, AIDS, and COVID-19.

 Pathogenic bacteria have a more varied operation and will often infect when the right opportunity arises so-called opportunistic infection. The infection caused by pathogenic bacteria is usually confined to a part of the body, described as a localized infection.

These infections may be caused by the bacteria themselves or by toxins (endotoxins) they produce. Examples of bacterial diseases include pneumonia, tuberculosis, tetanus, and food poisoning.

How Viruses Interact with Bacteria

Viruses can infect bacteria. Bacteria are not immune to viral hijackers which are known as bacteriophages viruses that infect bacteria. We don’t want to judge, but this may be one more reason to put viruses one notch higher in the nasty germs hierarchy.

What are Bacteria?

Bacteria are unicellular organisms that are of many different shapes and sizes. They are microscopic prokaryotes of Kingdom Monera. Bacteria contain a single chromosome composed of DNA and extra-chromosomal DNA called plasmids.

They live in every possible habitat including extreme environments such as hot springs and the deep sea. Interestingly they can live independently without the aid of other living organisms, unlike viruses.

Furthermore, they reproduce asexually by binary fission, which is the most common reproductive method of bacteria.  The most amazing fact is that, out of countless types of bacteria, most are harmless for human beings.

In fact, a vast majority of bacteria are beneficial to us as they break organic matter and kill parasites. Only a few of the bacteria cause diseases to human beings.

What are Viruses?

On the other hand, viruses are not living things and have no cells. However, they possess characteristics that lie between living and non-living things such as; they can evolve and have genes but, they do not metabolize nutrients, produce and excrete wastes, and cannot move around on their own.

Likewise, they are intracellular parasitic organisms that require a living host such as a plant or an animal to multiply. Hence, they penetrate the cells of a host and live inside the cells.

They change the genetic code of the cells of the host that starts to produce the virus. When enough baby viruses are produced by the cell, the host cell bursts, and the viruses come out and penetrate into other cells of the host. Thus, it can be said that viruses are not living things.

They only contain RNA and DNA and proteins that start to act on the information stored when a virus finds a host cell. However, all viruses are harmful, and the only way to remain healthy is to prevent viruses from entering our bodies.

Moreover, it is very difficult to destroy viruses, unlike bacteria which can kill by antibiotics. Antiviral vaccines can slow down the reproduction of viruses but cannot destroy them completely.

Main Difference Between Bacteria and Viruses

  • Bacteria and virus are infectious agents having different properties. However, not all bacteria are harmful. Thus, only a few percentages of bacteria cause harmful effects for us. In fact, most bacteria are beneficial to a human in many ways. For example, those bacteria residing in our gut. On the other hand, viruses are only harmful.
  • Bacteria are living organisms while the viruses are non-living particles.
  • Bacteria are usually 0.2 to 2 µm in size while viruses are 10-100 times smaller than bacteria.
  • Bacteria possess a simple cellular organization but, the viruses are acellular.

What are the Similarities Between Bacteria and Viruses?

  • Both bacteria and viruses can be seen under the microscope.
  • Also, both cause infections to human, animals, plant and other living organisms.
  • However, both can be controlled by medicines.
  • Besides, both types contain a genetic material within them.


What are 3 differences between viruses and bacteria?

Viruses are tinier: the largest of them are smaller than the smallest bacteria. All they have is a protein coat and a core of genetic material, either RNA or DNA. Unlike bacteria, viruses can’t survive without a host. They can only reproduce by attaching themselves to cells.

What are 4 differences between viruses and bacteria?

Bacteria are single-celled, living organisms. They have a cell wall and all the components necessary to survive and reproduce, although some may derive energy from other sources. Viruses are not considered to be “living” because they require a host cell to survive long-term, for energy, and to reproduce.

Which one is bigger a virus or a bacteria?

Viruses are even smaller than bacteria. They aren’t even a full cell. They are simply genetic material (DNA or RNA) packaged inside a protein coating. They need to use another cell’s structures to reproduce.

How do you know if a cold is viral or bacterial?

Bacterial Infections

  • Symptoms persist longer than the expected 10-14 days a virus tends to last.
  • Fever is higher than one might typically expect from a virus.
  • Fever gets worse a few days into the illness rather than improving.

What do virus and bacteria have in common?

Bacterial and viral infections have many things in common. Both types of infections are caused by microbes (bacteria and viruses) and are spread by things such as coughing and sneezing, contact with infected people, surfaces, food, water, pets, livestock, or insects such as fleas and ticks.

Are antibiotics for bacteria or virus?

What is an antibiotic? Antibiotics are medicines that fight infections caused by bacteria in humans and animals by either killing the bacteria or making it difficult for the bacteria to grow and multiply. Bacteria are germs.

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