The main difference between bacteria and viruses is based on their cellular structure and the way by which they multiply. Bacteria are unicellular organisms, whereas viruses are acellular and can multiply only after entering into a suitable host cell.
A bacterial cell contains cytoplasm, ribosomes and DNA, and is able to synthesize its own proteins. Most of the bacteria reproduce by binary fission. Viruses, on the other hand, contain either DNA or RNA surrounded by a protein coat called capsid, and in some viruses an outer envelope is also present. Ribosomes are absent in viruses.
After entering the host cell, the viral genetic material uses the cellular machinery for the formation of new virus particles. Viruses are generally smaller than bacteria, although their size may vary. Antibiotics can act against susceptible bacteria, but they are not effective for the treatment of viral infections.
Bacteria vs Virus – Comparison Table
| No. | Basis | Bacteria | Virus |
|---|---|---|---|
| 1 | Nature | A bacterium is a single prokaryotic cell. | A virus is not made up of a cell. |
| 2 | Size | A typical bacterial cell is about 1 µm. | A typical virus is about 100 nm. Some giant viruses overlap in size with small bacteria. |
| 3 | Visibility | Many bacteria can be seen with a light microscope. | Individual virus particles usually require an electron microscope. |
| 4 | Shape | Common forms are spherical (cocci), rod-shaped (bacilli) and spiral. | The capsid may be helical, polyhedral or complex. |
| 5 | Outer boundary | The cell is enclosed by a plasma membrane. | The capsid encloses the viral genome. An envelope lies outside it in some viruses. |
| 6 | Cell wall | Most bacteria have a wall containing peptidoglycan. It is absent in Mycoplasma. | No peptidoglycan cell wall is present. |
| 7 | Capsule and capsid | Some bacteria have an outer capsule. It lies outside the cell wall. | The capsid is a protein coat around the viral genome. |
| 8 | Lipid envelope | A plasma membrane is present in the bacterial cell. | Only some viruses have a lipid envelope, acquired from a host-cell membrane. |
| 9 | Cytoplasm | Present inside the cell membrane. | A virus particle has no cellular cytoplasm. |
| 10 | Location of DNA | Bacterial chromosomal DNA lies in the nucleoid region. No membrane-bound nucleus is present. | The viral genome is packaged within the particle, not inside a nucleus of its own. |
| 11 | Membrane-bound organelles | Generally absent in bacterial cells. | No cellular organelles are present in a virus particle. |
| 12 | Ribosomes | Bacteria have ribosomes for protein synthesis. | A virus has no ribosomes. It uses those of the infected cell. |
| 13 | Genetic material | The cell contains both DNA and RNA. DNA forms its genome. | The genome of a virus particle is either DNA or RNA. |
| 14 | Genome form | Most bacteria have a single circular chromosome. | A viral genome may be linear, circular or divided into segments. |
| 15 | Genome strands | The bacterial chromosome is double-stranded DNA. | Viral genomes may be single- or double-stranded DNA or RNA. |
| 16 | Plasmids | Additional DNA molecules called plasmids are present in some bacteria. | Separate bacterial-type plasmids are not part of a virus particle. |
| 17 | Enzymes | Enzymes carry out reactions within the bacterial cell. | Some viruses carry or encode enzymes, but the particle has no complete metabolic system. |
| 18 | Protein synthesis | Its own ribosomes make bacterial proteins. | Viral proteins are made by the host cell after infection. |
| 19 | Metabolism | Bacteria carry out metabolic activities, although their requirements vary. | No independent metabolism occurs in a virus particle. |
| 20 | Energy production | The cell has mechanisms to obtain and use energy. | A virus cannot generate energy on its own. |
| 21 | Growth | A bacterial cell can increase in size before division. | A virus particle does not grow in size before making another virus. |
| 22 | Multiplication | Usually by binary fission. One cell divides into two. | Viral parts are made in a host cell and assembled into new particles. The virus does not divide. |
| 23 | Host-cell requirement | Most bacteria can multiply without entering a host cell. Some, including Chlamydia, require one. | Production of new virus particles requires a suitable living cell. |
| 24 | Toxin production | Some pathogenic bacteria produce exotoxins. The outer membrane of gram-negative bacteria contains endotoxin (LPS). | A virus particle does not contain bacterial LPS endotoxin. Viral disease develops through other interactions with infected cells. |
| 25 | Laboratory cultivation | Many bacteria grow on artificial nutrient media. Some cannot be grown this way. | Viruses require living cells for cultivation; nutrient medium alone is insufficient. |
| 26 | Hosts | Different bacterial species live in the environment, on organisms or within them. | Viruses infect cells of animals, plants, fungi, bacteria and other organisms. |
| 27 | Attachment | Some bacteria attach to surfaces using structures such as fimbriae. | A virus attaches through its capsid or envelope proteins to suitable receptors on a cell. |
| 28 | Movement | Some bacteria move with flagella. Others are non-motile. | A virus particle has no bacterial flagella and does not swim by itself. |
| 29 | Endospores | Certain bacteria, including species of Bacillus and Clostridium, form endospores. | Viruses do not form bacterial endospores. |
| 30 | Dormant state | Some bacterial cells enter a dormant state; endospores are one example. | Some viruses can remain latent within host cells and reactivate later. |
| 31 | Mutation | Mutations occur in the bacterial genome. | Viral genomes also mutate. The rates differ among viruses. |
| 32 | Genetic exchange | Bacteria may acquire DNA by transformation, transduction or conjugation. | Some viruses exchange genetic material by recombination; segmented viruses may undergo reassortment. |
| 33 | Transmission | Routes depend on the bacterial species. Some spread through respiratory droplets, food or water. | Routes also vary among viruses. Some spread through droplets, while others use different routes. |
| 34 | Disease mechanism | Disease may result from bacterial invasion, inflammation or toxins. | Viral infection may damage infected cells and provoke an immune response. |
| 35 | Immune response | Bacterial structures and products can be recognized by the host immune system. | Viral proteins and infected cells can also trigger immune responses. |
| 36 | Gram staining | Many bacteria can be examined by Gram staining, which helps distinguish cell-wall types. | Gram staining is not used to classify virus particles. |
| 37 | Antibiotics | An appropriate antibiotic may act against a susceptible bacterium. | Antibiotics do not treat the viral infection itself. |
| 38 | Antiviral drugs | Antiviral drugs are not used to inhibit bacterial multiplication. | Specific antivirals are available for some viral infections. They act at particular steps of infection or replication. |
| 39 | Vaccines | Vaccines are available against some bacterial diseases. Toxoid vaccines target certain bacterial toxins. | Vaccines are also available against some viral diseases. |
| 40 | Drug resistance | Bacteria can develop resistance to antibiotics through several mechanisms, including drug inactivation. | Viruses can develop resistance to antiviral drugs through genetic changes. |
Difference Between Bacteria and Virus
- Nature- Bacteria are unicellular prokaryotic organisms. A virus is not made up of a cell.
- Size- Viruses are generally smaller than bacteria. A typical bacterial cell measures about 1 µm, while a typical virus is about 100 nm. The size is not the same in all bacteria or viruses.
- Structure- A bacterial cell has a plasma membrane, cytoplasm, DNA and ribosomes. A cell wall is present in most bacteria. The virus has its genetic material enclosed within a protein coat called the capsid. In some viruses, an outer envelope is also present.
- Genetic material- Both DNA and RNA occur in bacteria. The genetic material of a virus particle may be either DNA or RNA.
- Ribosomes- Ribosomes are present in bacteria and take part in protein synthesis. No ribosomes are present in the virus. Its proteins are made by the ribosomes of the infected cell.
- Metabolism- Bacteria carry out cellular metabolic activities. A virus cannot generate energy on its own.
- Multiplication- Bacteria usually reproduce by binary fission, in which one cell divides into two. A virus does not divide this way. Its parts are produced inside the host cell and then assembled into new virus particles.
- Host cell requirement- Most bacteria can grow without entering another cell. Some bacteria, however, are obligate intracellular organisms. For a virus, entry into a suitable living cell is required to produce new virus particles.
- Effect of antibiotics- Antibiotics can act against susceptible bacteria. They are not used to treat viral infections.
Similarities Between Bacteria and Virus
- Size- Bacteria and viruses are microscopic. They cannot be seen with the unaided eye. Their size is not the same, and microscopes are used to study them.
- Genetic material- Genes are present in both. In bacteria, the genetic material is DNA. It may be DNA or RNA in a virus.
- Proteins- Proteins form part of a bacterial cell and perform different cellular functions. In viruses, a protein coat (capsid) is present around the genetic material.
- Infection- Some bacteria and viruses can infect humans, animals and plants. Many bacteria do not cause disease.
- Transmission- Certain bacterial infections spread through respiratory droplets. This is also seen in some viral infections. The route of spread depends on the organism.
- Mutation- Changes can occur in the genetic material of bacteria and viruses. These changes may pass to new bacterial cells during multiplication, or to newly formed virus particles.
- Immune response- Infection by a bacterium or a virus can produce a response from the host immune system.
References
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