Bacterial Morphology – Size, Shape, and Arrangements

What is a bacterial cell?

 Bacteria are unicellular organisms that belong to the prokaryotic group where the organisms lack a few organelles and a true nucleus. that distinguished it from eukaryotes due to its difference in morphology     

What is the morphology of Bacterial cells?

      The morphology of a bacterial cell is the most distinguished property of a bacteria. It is a characteristic property of a particular species. The morphology of bacteria cells not only tells the shape but also decides its pathogenicity. Morphological traits of bacteria cells are an important factor in this is their adaptability and evolution.

There are many features like motility, and mode of nutrition, that are affected by the shape of bacteria. The bacterial cell wall is made up of peptidoglycan(murein), which is a polymer of sugars, alternating N-acetyl glucosamine (NAG) linked to N-acetylmuramic acid (NAM) and amino acids peptide chain. Change in the composition of the polymer and its consistency is credible for the various morphology and form of a bacteria cell.

What is the quantity of a bacterial cell?

       The unit of measurement used in bacteriology is the micron(micrometer) which is one thousand a millimeter. Bacteria are, in public one-tenth the size of the eukaryotic cell. On average, the size of bacteria ranges from 0.5 nanometers to 0.5 µmeters. However, they can be as tiny as 0.3 µmeters and as large as 0.7 µm.

       It has been examined that the size of bacteria has an important role in the survival of organisms. Since organisms are missing in such an environment, bacteria can use accessible resources. The high surface area-volume ratios also allow bacteria to take up all the nutrients required for survival while allowing steady growth and reproduction.

What is the bacterial shape?

        Most bacteria have a rigid cell wall that provides a definite shape to the bacteria while protecting the internal components. The wide diversity of shapes is defined by the bacterial cell wall and cytoskeleton. Bacteria with different shapes exist and have different physical features in the outside world, and these features help cells cope with and adapt to external conditions. some bacteria have a feature to form endospores through which bacteria can survive in extreme environmental conditions

Types of shapes

The following types of bacteria based on their shape under the light microscope are;

  • Cocci
  • Bacilli( Rod-shaped )
  • Spiral


            The ovaisacteria or spherical ones are included called cocci bacteria. These may either remain single or attached in groups. They appear flattened when placed in groups. It is assumed that coccoid forms were derived from rod-shaped organisms throughout evolutionary time.

 What are the arrangements of Cocci?

       Cocci bacteria can be arranged either singly, in pairs, in groups of four, in chains, clusters, or cubes consisting of eight cells. These cells remain attached division.


               This group contains bacteria that are present as a single cell.  A coccus is any bacterium or archaeon that has a spherical, ovoid, or commonly round shape.


    This arrangement results when two bacterial cells happen as a pair( joined together). Some of the cells in this appointment might stay spherical while some might appear flattened, elongated, or bean-shaped. Examples; Streptococcus pneumonia, Moraxella catarrhalis, Enterococcus spp, and Neisseria gonorrhea.


     Tetrad bacteria are arranged in a group of four cells that remain attached and grow in the attachment after division. This arrangement results when the cells divide into four planes. Examples; are Aerococcus, Pediococcus, and Tetragenococcus.


       In this formation, the bacterial cells form a group of eight cells. This occurs when the cells divide in a perpendicular plane. The common characteristic associated with these organisms is being a strict anaerobe. For example;  Sarcina aurantiaca, Sarcina lutea, and Sarcina ventriculi.


           Here, the bacteria are organized in long chains. These bacteria are present in the family Streptococcus, which is characterized by a lack of motility and Gram-positive bacteria. For example; Streptococcus p genic, Streptococcus pneumonia streptococcus mutants.


     This type contains bacteria that are organized in grape-like clusters. This results from cell division in both planes and is characterized by motile organisms and Gram-positive. For example; Staphylococcus epidermidis, Staphylococcus haemolyticus Staphylococcus aureus, and Staphylococcus capitis.


             These are rod-shaped cells that like cocci, remain either single or attached to other cells. Bacilli bacteria are among the first bacteria to have occurred, and this pattern is said to be not as beneficial as other shapes. This has been inferred from the observation of the behavior of filamentous E.coli cells which, Though motile and chemotactic, move gradually, and cannot tumble to shift direction.

What is the arrangement of Bacilli?


    Bacilli are rod-shaped bacteria and are present as single cells. Those bacteria can form endospores and are facultative anaerobes. For example; Salmonella enterica subsp, Bacillus cereus, Bacillus anthracis, and Salmonella choleraesuis.


      As in Diplococci, Diplobacilli also occurs in pairs. After cell division, the two cells do not divide and grow in an attached structure. For example; Coxiella burnetii, Klebsiella rhinoscleromatis, and Moraxella Bovis.


    In this group, bacteria are organized in chains. This impacts form cell division in a single chain. For example; Streptobacillus moniliformis, streptobacillus Levaditi, Streptobacillus felis, Streptobacillus hongkongensis.


      As the name refers, coccobacilli resemble both cocci as well as bacilli. These are shorter in extent and thus, occur stumpy. For example; Chlamydia trachomatis, Haemophilus influenza, and Gardnerella vaginalis.


Palisades are the type of bacilli bacteria that resemble a picket fence structure as a result of the bent at the point of division during cell division in bacteria. They appear similar to Chinese letters. For example; Corynebacterium diphtheria causes diphtheria.


           This group contains bacteria that are either helical-shaped or curved(comma-shaped). The bacteria can range from slightly curved to corkscrew-like spirals.

What is the arrangement of the spiral?


Any group of comma-shaped bacteria in the family vibrionaceae. These are slightly curved bacteria resembling a comma shape. For example; Vibrio mytili, Vibrio anguillarum, vibrio parahaemolyticus, and vibrio cholera.


     Any group of spiral-shaped bacteria, some of which are serious pathogens for humans, causing diseases such as syphilis, yaws, Lyme disease, and relapsing fever. They are spiral bacteria having a helical shape. These are creative and have an axial filament which supports in motility. These filaments are essential and distinguished characters between spirochetes and other bacteria.

       These filaments run throughout the length of the bacteria and thus, help in twisting the motion of bacteria. For example;  Leptospiraspecies (Leptospira interrogans), Treponema pallidum, Borrelia recurrentis.

Spirilla (Helical-shaped/ Corkscrew form):

         They are gram-negative bacteria and are distinguished by motile structures known as flagella. These bacteria are similar in structure to spirochetes but are more rigid. They, too, have a flagellum but lack the no flagella like in spirochetes. For example; campylobacter jejuni, Helicobacter pylori, and Spirillum winogradskyi.

 What are the other shapes and arrangements of Bacterial cells?

   Appendaged Bacteria;

              The bacteria that produce a unique structure like pills or fimbriae are called Appendaged bacteria. These bacteria are more infectious than other bacteria that do not form these appendages. For example; Neisseria gonorrheae, the agent of gonorrhea.

Box-shaped /Rectangular Bacteria:

    Box-shaped bacteria are rectangular and resemble a box. For example; Haloarcula marismortui.

Club-shaped Rod Bacteria:

    These bacteria are long, thin, and filament-shaped. They, sometimes, divide to construct branches corresponding to strands of hair or spaghetti called mycelium. For example; Actinomycetes.

Triangular-shaped Bacteria:

      This group includes bacteria that are triangular. For example; Haloarcula.

Pleomorphic Bacteria;

      The bacteria that do not have a restricted shape are contained in this group. They can change their shape, but in ethical culture, they occur to have a definite form. For example; Mycoplasma pneumonia, and M.genitalium.

Stalked Bacteria;

   These are the bacteria that contain a stalk on one end of the cell. For example; Caulobacter crescentus.

Star-shaped Bacteria;

    These bacteria look like stars or are star-shaped and are included in this group. For example; Stella humosa.

Why is important to know about the morphology of bacterial cells?

              It is important to understand the morphological structure of bacteria, as it gives us a better understanding of microbial physiology, pathogenic mechanisms, and antigenic features, and enables us to observe them by species.

Rimsha Bashir
Rimsha Bashir

Rimsha Saith is a highly knowledgeable microbiologist with a keen interest in the field. Her expertise and passion are in her writing for Microbiology. As a writer, Rimsha has authored numerous articles that have been well-received by both health and medical students and industries.

Articles: 43

Newsletter Updates

Enter your email address below and subscribe to our newsletter

Leave a Reply

Your email address will not be published. Required fields are marked *