Difference between Bacteria and Virus

Key Difference: Bacteria are single celled and prokaryotic organisms. They replicate in an asexual manner. They can be harmful as well as beneficial; it depends upon the type of bacteria. On the other hand, Viruses are non living pathogens and are acellular. A Virus also needs a host cell in order to reproduce.  Most of the Viruses do not serve any useful purpose.

Bacteria are single cell plant organisms and they are very small in size, measuring about a few microns in size (micron=0.001mm). Bacteria are different from other cellular forms as they do not have any nucleus. Many of the Bacteria also inhabit our skin, mouth and intestine. They help in digestion and also keep the number of bad bugs under control.

On the other hand, Virus is a mobile genetic material that is enclosed in a protein or a fatty shell. They are smaller than bacteria, ranging between (0.1 to 0.3 microns) in size. They were discovered just before 1900, and were known as filterable Viruses due to their small size. A debatable issue is regarding their status as living or non living. This is due to the fact that they consist of merely nucleic acid that is wrapped in a coat of protein.

The characteristics are listed below:-





Most bacteria consist of a ring of DNA surrounded by a cellular machinery, contained within a fatty membrane.

They consist of little more than a small piece of genetic material surrounded by a thin protein coating. Some are also surrounded by a thin and fatty envelop.

Covered by

A cell wall that consists of polysaccharides, protein and lipids.

A sheath made-up of proteins known as capsid.

Cell membrane

Present below the cell wall

No cell membrane

Genetic Material




Comparatively large (approx 100 times)

Comparatively small


Intercellular organisms

Intracellular organisms


Comes in three different possible shapes


Cocci = sphere shape

Bacilli = rod shape

Spirella = spiral shape

Viruses come in all different shapes

Some viruses are shaped like a space ship.  They are called bacteriophages.


Needs a living host, like a plant or animal

Can grow on non-living surfaces


Some are useful

Mostly are harmful


Kill Bacteria

Cannot kill Viruses

Diseases Caused

Cholera, tuberculosis, lyme disease, pertussus, salmonella, staph infections, strep throat, leprosy, tetanus, diptheria, E.coli, flesh eating (necrotizing fascitis) and ricketts. 

Flu, colds, HIV/AIDS, hepatitis, west nile, measles, herpes, shingles, chicken pox, monkey pox, polio, smallpox, ebola, and some cancers (epstein-barr) are just a few viruses that affect humans and animals.

Source of Energy

Seize energy from the same essential sources as humans, including sugars, proteins, and fats

Seize materials and energy from host cells by hijacking cellular machinery



Characteristics of both living and non-living

How they are transmitted

Direct contact with an infected person

Contaminated food or water (Salmonella, E.coli)

Dirty objects (tetanus)

Infected animals (rabies)

By direct contact with infected individuals

By contact with contaminated objects (such as toys, doorknobs)

By inhalation of virus-laden aerosols. (think sneezes)

By animals that act as hosts (vectors)


Bacteria reproduce through binary fission, they split into two cells.

Virus injects itself into a living cell

Protein coat is discarded

Hereditary material takes over the cell’s activities

Virus reproduces and the cell fills

Cell splits open

Viruses leave the cell and attack new cells


Bacteria move through the environment using a structure known as the flagellum.

Viruses do not have structures and thus cannot move on their own.

Images Courtesy: assignmentpoint.com

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