Difference Between Bacteria And Virus

What’s the difference between a bacteria and a virus? You might think that’s a strange question to ask, given that both are micro-organisms, meaning that neither can be seen by the naked eye. Both can make us vomit, give us diarrhea, fever and even challenge us with life-threatening diseases, but what differences lie between them?

Are they both bad?

First and foremost, they are both not evil monsters. Viruses are definitely bigger villains than bacteria.

For starters, bacteria form a part of our “normal flora” and trillions of them live inside us without causing any harm. They are beneficial because they can improve digestion and protect us against infections. Bacteria like lactic acid bacteria (LAB), mostly of the species Enterococcus and Lactobacillus are associated with the fermentation of food; these fermented foods impart health benefits to those who eat them.

Viruses do no such thing! They are like those selfish people in our lives who use us when they need and then forget about us later. Viruses cannot grow without a host, because they need a host to multiply and flourish, so they use the host as their platform for multiplication and then destroy the host. Quiet evil, wouldn’t you agree?

Bacterial infection vs viral infection – how are they different?

More proof that bacteria and viruses are different lies in the fact that when you go to a doctor with a sore throat and fever, the doctor sometimes puts you on antibiotics, but other times he/she will let the infection simply run its course. This is because bacterial infections can be treated with antibiotics, but antibiotics are ineffective against viral infections. Thus, if you are experiencing a viral attack and are taking antibiotics, you may feel no difference in your condition, but if it’s a bacterial infection, then the antibiotics will attack and kill the bacteria, making you feel better faster.

This aspect of deciding on treatment modality makes it clear that understanding the basic differences between a bacteria and a virus is critical. Let’s start by establishing a brief understanding of both.

Bacteria – The Tiny Warriors

Bacteria are unicellular (single-celled), prokaryotic (without a membrane-bound nucleus or organelles) microscopic organisms that divide by binary fission. They typically range in size from 0.5-1.5 μm, but can also be in the 1-3 μm range. Being so tiny, they can be seen using a light or electron microscope. They are both beneficial and harmful to us. They exist everywhere around us – in the air, water, soil, our body… you name it and they’re there!

Viruses – Tiny Packets Of Genes

Viruses are infectious agents that lack a cellular structure. They do, however, contain viral genetic material – either DNA or RNA, but never both. This genetic material is enclosed in a highly specialized protein coat that protects the genetic material when the virus is outside the host cell, but also helps the virus enter a weak host cell. Since they have no cellular structure, but do contain genes, viruses are nothing but tiny packets of genes moving from host to host.

Viruses are much smaller than bacteria and range from about 0.015 – 0.2 μm. They are so small that they cannot be seen under a light microscope and need an electron microscope to be studied. A better way to imagine the size of a virus is to think of a car as a bacterium; a football sitting next to the car would be a virus!  Viruses can only grow inside a host cell by means of replication (replicas of the virus are created within the host cell) and are dependent on the host cells to carry out vital functions. They are therefore called “obligate intracellular parasites”.

Bacteria vs Viruses

bacteria vs virus

Size0.5-1.5 μm typically0.015 – 0.2 μm
MicroscopyLight or electron microscopyOnly electron microscopy
No. of cellsUnicellularNo cells – they are small packets of genes!
Cell wallPresentAbsent – protein coat present instead.


Genetic materialDNA or RNA floating in cytoplasmDNA or RNA enclosed in protein coat
ReproductionAsexual – replicates by binary fissionReplication inside the host cell – “obligate intracellular parasites”
Growth in artificial laboratory mediaPossibleNot possible – tissue culture needed
InfectionGenerally localizedSystemic
TreatmentAntibioticsAnti-viral drugs
Cellular machineryPresentAbsent
Practical significanceSome cause disease;

Some improve digestion;

Some contribute to our immunity against pathogens.

Some perform important roles in recycling elements that contribute to soil fertility,

Some spoil food,

Some ferment and make food like yogurt.


Cause diseases in humans, other animals, plants and even other micro-organisms.


  1. National Institutes Of Health (NIH) (Link 1)
  2. National Institutes Of Health (NIH) (Link 2)
  3. Book Microbiology – by Pelczar, Reid, Chan
The short URL of the present article is: http://sciabc.us/QWlxj
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About the Author:

Dr. Maneka Vig is an experienced dental surgeon with 8 years of dental practice behind her. She completed her Bachelors in Dental Surgery (BDS) from Maharashtra University of Health Sciences in India and ran her own dental practice for many years. She then spearheaded the branch operations for one of India’s largest dental chains as a head dentist for a designated branch wherein she was responsible for rendering treatment, managing operations of the practice and headed a team of efficient doctors. Being passionate about science and academia, she ventured into medical writing and worked with a reputed healthcare communications firm.

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