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Bacterial taxonomy

Bacterial taxonomy

The science in which the bacteria are classified is called bacterial taxonomy. The taxonomy is the combination of two words that is taxis means arrangement and nomos means to distribute or govern. This bacterial taxonomy refers to the three disciplines that are

  1. Classification
  2. Nomenclature
  3. Identification



Classification refers to the arrangement of bacteria into groups and sub-groups. They are classified on the basis of their mutual similarities and evolutionary relatedness. Bacteria are classified by using Carl Linneous method. This type of classification is used to classify the bacteria. The bacteria are classified on the kingdom Monera.

Taxonomy rankSuffix


These bacteria are classified into different domains on the basis of

  • Cell wall made of peptidoglycan that is different from other cell walls.
  • Bacteria don’t have membrane-bound organelles.
  • Bacteria don’t have the membrane-bound nucleus for the genetic material
  • Electron transport chain occurs in the cell membrane
  • Bacterial cytoskeletons have tubulin related proteins and actin-related bacterial proteins that provide support to the cell.
  • They have bacterial chlorophylls and carotenoids that are responsible for fixing carbon dioxide.
  • Asexual reproduction is through binary fission, fragmentation and


Bacteria can be classified on the basis of follows.

Bacterial morphology:

Bacterial morphology deals with the shape of bacteria. These are present in three shapes.

  • Cocci:

Cocci are the bacteria that have spherical symmetry. They are observed as circle under microscope. They resemble as tiny balls in the microscope.

E.g. Streptococcus pneumoniae and Staphylococcus aureus.

  • Bacilli:

These are rod shape bacteria under the microscope. Their width and length vary from bacteria to bacteria. They resemble as pilli of bacteria. They may have square ends or round ends.

E.g. Bacillus anthracis

  • Spiral:

Some bacteria have spiral like morphology. They are twisted and helical symmetry that resemble like corkscrews.

E.g. Helicobacter pylori and Vibrio cholera

Bacterial arrangements:

They may arrange as single, double, chains and clusters. These arrangements depend on the dimension of the microbial cell division.

  • Single:

Some bacteria appear as single cell under a microscope. These bacteria divide into one dimension.

  • Diplo:

Some bacteria appear as pair or double cells. Two single cells combine together and form a diplo cells. These cells also divide in one dimension.

  • Tetrad:

Some bacteria arrange themselves in the pair of two. These are present as 4 bacteria arranged themselves to give a tetrad shape. These bacteria divide in two dimensions.

  • Strep:

These bacteria are present in the form of chains. They seem as long chains under the microscope. Their cell division also occurs in one dimension.

  • Staph:

These bacteria are present in the form of clusters under the microscope. They look like as grapes under the microscope. The cell division of these bacteria occurs in random conditions.

Nomenclature of bacteria:

Nomenclature of bacteria is a method of giving the names to the bacteria. There are many ways to give name to the bacteria.

  • Arrangement:

Bacteria can be named according to their arrangement. There are many bacteria that are named according to their arrangements. For example; staphylococcus is named after their arrangement in bunch form. Streptococcus is named because of the chain-like arrangement.

  • Shape:

Bacteria can be named according to their shape. There are many bacterial names that are because of their shapes. For example; cocci is the circular shape of bacteria that represent a large group of bacteria. Bacilli are the rod-shaped bacteria that are named after their rod shape.

  • Scientist name:

There are many bacteria that are represented by their scientist name. The scientist that discovered the bacteria name it with their name as a sign of honour. For example; Listeria monocytogenes is named after the discovery of his scientist Joseph listeria. Escherichia coli are named because of their scientist name Theodor escherich.

  • Place of discovery:

The bacteria can be named from the place where the bacteria discovered. The bacteria are discovered from the place and some scientist give them the name of the place. For example; Thermus aquaticus is named after isolated from the hot springs.

  • Type of disease caused:

Bacteria can be named by the type of disease they develop in the organism. There are many diseases that are used to giving name the bacteria. Bacterial pathogenesis helps the scientist for giving the name to the bacteria. For example; Bacillus anthracis is name after that it is the causative agent of disease anthrax. Mycobacterium tuberculosis is responsible for tuberculosis in the organism that’s why it is known as tuberculosis.


Bacteria are identified by using many techniques. The procedure for the bacterial identification is as follows:

  • Gram staining:

Gram positive bacteria have a thick wall of peptidoglycan. Their cell wall is composed of peptidoglycan, lipopolysaccharides and teichoic acid. They have multilayers of peptidoglycan. The cell wall thickness is 100-120 Å. It is single-layered that have low lipid content, whereas murein content is 70-80%. For example; Bacillus anthracis

Gram negative bacteria have a thin wall of peptidoglycan. Their cell wall is composed of peptidoglycan, lipopolysaccharides. They have a high percentage of lipids in their cell wall. Teichoic acid is absent in their cell wall. They have a single layer of peptidoglycan. The cell wall thickness is 70-120 Å. It is a two-layered cell wall that has 20-30% lipid content and is 10-20% murein content. For example; Salmonella enteritidis

  • Media growth:

Bacteria grow on simple, differential or selective media. On different media, bacteria give different colony type. On selective media, only selective bacteria grow and other bacterial growth suppress by using chemicals. For example, on EMB agar, only Escherichia coli grow because it contains eosin and methylene blue that suppress the growth of other bacteria.

  • API kits:

API kits are the biochemical tests that are used to differentiate the bacteria. These biochemical tests are specific for every bacterium and used to identify the bacteria. These kits are commercially available in the market. It is the easiest method to identify the bacteria.

  • Molecular techniques:

Molecular techniques such as polymerase chain reactions, gel electrophoresis and restriction fragment length polymorphism is used to identify the bacteria. These techniques are accurate and used in advanced studies to identify the bacteria. 16sRNA are sequenced as they are specific for bacteria. These sequences are specific for genus and by using these sequences, the bacterial genus is identified. By using the whole sequencing of the genome, species can be identified.


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