What is the differences between Virus and Bacteria?

The microbial species are found naturally in the environment. The bacteria community competes for space and resources with other species and studies reveal that with mixed or pure cultures, bacteria can kill or impair other microbes for survival and can impact the outcome of competition in nature. Bacteria are the simplest and most abundant living organisms. Bacteria is a single-celled microorganism without a nucleus and other cell organelles hence classified as prokaryotic organisms since they lack well-defined nuclei and membrane-bound organelles.

In addition, their chromosomes are composed of a single closed DNA circle and come in different shapes and sizes from minute spheres, cylinders, spiral threads, flagellated rods, or filamentous chains.


The Bacteria structure is simple and exhibits one of three basic structures:

  • Bacillus (plural, bacilli), straight and rod-shaped.
  • Coccus (plural, cocci), spherical-shaped.
  • Spirillus (plural, spirilla), long and helical-shaped called spirochetes. Spirilla bacteria have complex structures within their membranes that allow them to spin and propel.

Bacteria are too small to see with a naked eye and characterized by the prokaryotic cellular organization. Although bacteria cause infections, they make possible many essential functions in the ecosystem such as capturing nitrogen from the atmosphere, aid in the decomposition of organic matter, as well as photosynthesis in many aquatic communities.

For example, bacterial photosynthesis is thought to be the source of much oxygen in the earth’s atmosphere. Bacteria are the only organisms capable of fixing atmospheric nitrogen. They are classified based on their metabolic and genetic characteristics, but only when they are grown on a defined medium since their characteristics often change depending on their growth conditions.

The main difference between bacteria and other organisms is that they live everywhere even in extreme environments that would be lethal to other organisms. Such environments include in hot springs, in hypersaline environments, and in atmospheres rich in toxic gases such as methane or hydrogen sulfide. It is likely that bacteria evolved to adapt to these harsh conditions since bacteria have been present since the day life began on the earth. Noting that the harsh conditions were present when in the early earth.


On the other hand, viruses are tiny obligate intracellular parasites that contain either a DNA or RNA genome. They are seen as mobile genetic elements of cellular origin. Viruses depend on specialized host cells for the supply of complex metabolic and biosynthetic machinery of eukaryotic and prokaryotic cells. A complete particle of a virus is called a virion and the main function of a virion is to deliver its DNA or RNA genome into the host cell for the genome to be expressed through transcription or translation by the host cell.

Basically, the viral genome has associated basic proteins and is packed in a symmetric protein capsid. The nucleic acid-associated protein (nucleoprotein) together with the genome form the nucleocapsid which is surrounded by a lipid bilayer are derived from the host cell membrane that is modified and studded with an outer layer of virus envelope glycoproteins.

Characteristics of Bacteria

Bacteria vary in shapes and the characteristic morphology of the species is maintained through generations but is periodically modified within set limits during bacterial division and lifecycles. Bacterial morphology is a constant and active process that is guided by robust regulatory circuits. The shape dictates the interaction between a bacterial cell and its environment in motility, the formation of multicellular aggregates, habitat colonization, predation, and resistance.

Characteristics of Viruses

Viruses are infectious organisms and there are those that infect only bacteria called the bacteriophages and those that infect fungi only, called mycophages. Those that infect other viruses are called virophages. Viruses reproduce at a fast rate and can mutate but only in a living host. On the other hand, they are acellular meaning they do have a cytoplasm or cellular organelles. They do not carry out metabolism on their own therefore replicate through the host cell metabolic machinery.

Basically, viruses do not grow and divide but new components are synthesized and assembled within the infected host cell. Furthermore, most viruses possess either DNA or RNA but not both.

How do a bacteria infect human?

Infections from bacteria are as a result of a disturbance in the balance between bacterial virulence (the ability to cause severe disease in the host) and host resistance (when the host species resist certain strains of a pathogenic species). The main objective of bacteria is to multiply rather than cause disease. Alternatively, the resistance of the host has enhanced phagocytic cells and an intact immune system. Nevertheless, specific immunity develops over time.

How virus cause infections?

The pathogenic mechanisms of viruses include implantation of the virus at the point of entry, virus replication, spreading to the target organs or disease sites, and spreading to sites of shedding of virus into the environment
Generally, microbes

  1. Gain access to the host (contamination)
  2. Adhere to the host (Adherence)
  3. Replicate on the host (Colonization)
  4. Invade tissue (invasion)
  5. Produce toxins or other agents that cause host harm (damage)


Bacteria and viruses begin to colonize our bodies from the moment we are born and it is because of their ability to adapt to their environments. Viruses are packets of nucleic acid with either DNA or RNA. Outside a host cell, a virus is dormant and it is only after it enters a host cell and uses its metabolic machinery to produce copies of itself it is able to burst out of infected cells. Bacteria carry a single circular molecule of DNA that encodes the essential genes for reproduction. Bacteria carry only one set of chromosomes instead of two. The major difference is that Bacteria survive on appropriate media, stain gram-positive or negative while Viruses only replicate intracellularly


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Al-Mohanna, M. T. (2016, March). Bacterial introduction.

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