The 3 differences between viruses and bacteria

Viruses and bacteria often produce similar clinical pictures in affected patients.

Several studies point out that this may be due, in part, to the fact that cellular immune responses to the two pathogens share several similarities. However, the treatments for a viral or bacterial infection are very different, so knowing the differences between viruses and bacteria is essential.

Although both view microscopic organisms as potentially pathogenic to humans, other animals, and plants, there are many more factors that set them apart than there are qualities that unite them. Here we show you some of the most important differentiation characteristics between viruses and bacteria.

    Main differences between viruses and bacteria: the question of microscopy

    Before discussing the many differences between these microorganisms, it is always good to remember the attributes that unite them. Some of them are:

    • Viruses and bacteria can be considered germs because they are microorganisms with pathogenic potential.
    • They move on microscopic scales (from micrometers to nanometers in length), although viruses are much smaller.
    • Unlike the cells of eukaryotic living things, the genetic information of both is not compartmentalized in a nucleus.
    • Infections caused by both activate the immune system, generating general inflammatory responses and episodes such as fever.

    All of these similarities are very superficial, Because as we will see below, the differential elements are much more numerous. We then explored them.

    1. Morphological differences

    The differences between viruses and bacteria are so abysmal that there is a heated debate in the scientific community, as there is no doubt that bacteria are living things, but that cannot be said if we are talking about viruses.

    In general, several studies conclude that viruses are structures of organic matter that interact with living things, but that they are not biological forms per se. Because?

    1.1 Acellularity

    According to the definition of official organisms, a cell is a “fundamental anatomical unit of all living organisms, usually microscopic, consisting of a cytoplasm, one or more nuclei and a membrane that surrounds it”.

    This requirement is satisfied by bacteria, Since although they present only one cell that makes up the whole of its body, it has all the requirements to be considered a living form. The bacterial cell is made up of the following:

    • Pili: external hairy agents having the function of surface adhesion or gene transfer between bacteria.
    • Capsule: the outermost layer of the bacteria, formed by a series of organic polymers. It protects it from adverse environmental conditions among others.
    • Cell wall: under the capsule. It supports osmotic pressures and cell growth.
    • Cytoplasmic membrane: under the cell wall. Phospholipid bilayer that defines the shape of the cell.
    • Cytoplasm: internal part of the bacterial cell, which contains the cytosol and organelles.
    • Ribosomes: organelles responsible for protein synthesis.
    • Vacuoles: storage structures for substances and waste.

    All of these characteristics are common to the complex cells that make up eukaryotic organisms, but for example bacteria lack mitochondria, chloroplasts, and a delineated nucleus. Speaking of nuclei and genes, these microorganisms have their genetic information in a structure called a nucleoid, Which consists of a free circular DNA double strand closed by a covalent bond.

    As we have seen, bacteria have a unicellular structure not as complex as that of the cells that make us up, but which is also not below from a biological point of view. In the case of viruses, we have much less to explain:

    • They present one or more segments of RNA or DNA, double or single stranded.
    • Capsid: cover formed by the repetition of a protein (capsomer) that protects genetic information.
    • Wrapper: present only in certain types of viruses. Lipoprotein wrap that surrounds the capsid.

    Therefore, the structure of viruses does not meet the requirements to be considered a cell. If this is the minimum basis of all living things, are viruses biological organisms? Due to its acellularity, in the strict sense, we can say no.

      1.2 Morphological diversity

      Due to its greater biological complexity, bacteria come in a variety of forms. Some of them are:

      • Coconut, spherical in shape. Diplococci, tetracocci, streptococci and staphylococci.
      • Bacilli, stick-shaped.
      • Spiral bacteria. Spirochetes, spirals and vibrations.

      In addition, many bacteria have flagellar structures that allow them to move around in the environment. If they have a single flagellum, they are called monotric, if they have two (one at each end) lophoteric, if they have a cluster at one amphitric end, and if they are distributed throughout the body, perimetric . All this information highlights the bacterial morphological diversity.

      When we talk about viruses we find, once again, a much darker structural landscape. There are helical, icosahedral, enveloped shapes, and some with slightly more complex shapes that don’t fall into any of the previously named groups. As we can see, its morphology is very limited.

        2. A differential reproduction mechanism

        Perhaps the biggest difference between viruses and bacteria is the way they infect the host and multiply within it. So we do not immerse ourselves in the world of reproduction of these microorganisms.

        2.1 Bipartition

        Bacteria, both free and pathogenic, usually reproduce asexually by bipartition. The entire genome of the cell replicates exactly before each reproductive episode, because unlike eukaryotic cells, bacteria are able to replicate all of their DNA throughout the cell cycle. This happens through replicons, units with all the information needed for the process.

        To keep it simple, we’ll limit ourselves to saying that the cytoplasm of the bacteria is also growing, and when the time comes, a division occurs in which the parent bacteria divides into two, each with a genetically equal nucleoid.

        2.2 Replication

        For viruses to multiply, the presence of a eukaryotic cell that can be secreted is essential.. Viral replication is summarized in the following steps:

        • Adhesion of the virus to the cell to be infected.
        • Penetration, entry of the pathogen into the host cell by a process of endocytosis (typical viroplexy, penetration or fusion).
        • Stripping, where the capsid of the virus breaks down, leaving genetic information free.
        • Replication of the virus’s genetic information and synthesis of its proteins, sequestering the biological mechanisms of the infected cell.
        • Assembly of the viral structure within the cell.
        • Release of new viruses by cell lysis, breaking their walls and terminating them.

        The replication of viral genetic information is very varied, because it all depends on whether it is made up of DNA or RNA. The essential idea of ​​this whole process is that these pathogens sequester the mechanisms of the infected host cell, forcing it to synthesize the nucleic acids and proteins necessary for its coupling. This difference in reproduction is essential for understanding viral biology.

        3. A diversified biological activity

        This difference between viruses and bacteria in terms of reproduction, they condition the biological niches in which the two microorganisms develop.

        Bacteria are prokaryotic organisms that can be parasitic or free because they do not require an external mechanism to multiply. In the case of pathogens, these require the environmental conditions or nutrients of the organism in which they invade in order to thrive and survive.

        However, intrinsically and theoretically, if there was a non-living organic environment with all the qualities of the body of the infected, they would not have to invade it. Therefore, many pathogenic bacteria can be isolated from culture media under laboratory conditions.

        The case of viruses is completely different, because their existence cannot be conceived without a cell to parasitize. Some viruses are not harmful on their own as they do not cause harm to the host, but they all have in common the requirement of the cellular mechanism for its multiplication. That is why all viruses are considered obligatory infectious agents.


        Viruses and pathogens are microscopic agents that can be considered germs in the strict sense of the term, because they parasitize and benefit from a living being. However, in the case of bacteria, there are thousands of living species, which also play a vital role in the Earth’s biogeochemical cycles (such as the fixation of atmospheric nitrogen).

        Viruses, on the other hand, are infectious agents that in many cases are not even considered living things. This does not mean that they do not perform important functions, as they are an essential means of horizontal transmission of genes and major drivers of biological diversity. The relationship between virus and host is a constant biological race, as both evolve at the same time, one to infect and the other to prevent or fight infection.

        Bibliographical references:

        • Pitha, PM (2004). Unexpected similarities in cellular responses to bacterial and viral invasion. Proceedings of the National Academy of Sciences, 101 (3), 695-696.
        • Betancor, L., Gadea, M. and Flors, K. (2008). Bacterial genetics. Institute of Hygiene, Faculty of Medicine (UDELAR). Subjects in bacteriology and medical virology. 3rd ed. Montevideo: FEFMUR Book Office, 65-90.
        • Brock, TD, Madigan, MT and Abad, VT (1993). Microbiology (No. 579.2 BRO). Mexico: Prentice Hall Hispanoamericana.
        • R. Arbiza, J. Viral biology. Retrieved July 11 from
        • Ruchanksy, D. Introduction to virology. Retrieved July 11 from

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