Classification & Nomenclature Invitation.

Classification and Nomenclature in Microbiology | Taxonomic Categories

Nomenclature is the set of rules and conventions which preside over the naming of taxa, while Classification is the grouping of organisms on the basis of phylogeny and phenotype. The science of Classification, Nomenclature, and identification is known as Taxonomy. In this vast living world, having a system of naming and grouping bacteria and other micro-organisms becomes a necessity and hence we have Classification and Nomenclature to maintain clarity and avoid any confusion.


It is a system that follows certain set of rules to organize the objects or population into different groups based on the similar characteristics. The similar set of rules is used in life sciences to divide or categorize the diverse life forms. It is needed because every organism has originated and evolved from an ancestor. The classification system permits us to study the interrelation between organisms. The classification allows us to do systematic studies of all life forms. Since the Microbial world is as diverse as plant and animal world, a similar classification system is used in Microbiology.

Carolus Linnaeus, the Swedish Zoologist, Botanist, and a Physician developed the classification system, and published it in his Systema Naturae booklet. He created a standard system for categorizing the organisms. Through his life, he kept on updating his booklet, and published it in multiple volumes. Owing to his immense contribution, he is known as the Father of Taxonomy.

The 7 taxonomic level classification was contributed by many scientists, few of them have been listed below –

Domain by Carl Woese

Kingdom by Whitakker

Phylum by Ernst Haeckel

Class and genus by Carolus Linnaeus

Species and sub species by Ernst Mayr

Taxonomic categories are as follows-

Domain (Bacteria, Archea, and Eukarya)

Kingdom (Archeabacteria, Eubacteria, Protists, Fungi, Plantae, and Animalia)



Genus (Generic name)

Species (specific name/specific epithet)

Sub species


Domain – Bacteria

Kingdom – Bacteria

Phylum – Proteobacteria

Class – Gammaproteobacteria

Order – Enterobacteriales

Family – Enterobacteriaceae

Genus – Escherichia

Specie – Escherichia coli

Why classification is important in Microbiology?

  1. It allow us to conduct systematic studies of Microorganisms
  2. For identification of Microorganism.
  3. To study inter relationship among the microbes.
  4. To study their diversity.
  5. Classification allows us to develop different branches of Microbiology like Virology, Mycology, Bacteriology, and Parasitology etc.


Nomenclature is the system that consists of set of rules for scientific naming the organism. Before the establishment of any nomenclature system, people used to name by using common or vernacular language. Due to which the names would differ from language to language, and from one geographical area to other. To conduct systematic studies, it is important to have common and same name of the organism across the globe. Understanding this need, some rules were set for scientific naming.

The first system that came into existence was Polynomial naming in 1750. In this system, the names of the organisms used to be very long, containing more than three Latin words. Every word used to describe characteristics of that particular life form. These lengthy and descriptive names were difficult to remember. Hence, the polynomial naming system was rejected due to following reasons –

  1. Very lengthy.
  2. Very difficult to remember.
  3. The chosen characteristic for naming may be different from scholar to scholar.

Due to the rejection of Polynomial Naming system, people came up with an alternative method called as Trinomial naming system. In the Trinomial system, the organisms were named by their genus, species and sub species. The problem with trinomial system was that, the subspecies names were regional and varied from one geographical area to another.

Binomial naming system:

Carolus Linnaeus developed the Binomial system. According to this system, only two names were given to an organism based on its genus and species. To standardize the naming, following set of rules were set –

  1. Each organism name would consist of two words, one to represent genus and other for species.
  2. Two species of the same genus should not have same species or specific name.
  3. While writing the name, the genus name is always written first and followed by species name.
  4. The genus name always begins with capital alphabet.
  5. The species name always begins with small alphabet.
  6. When the scientific names are typed or print, it should always be in italics.
  7. When the scientific names are hand written, the names should be under lined.
  8. The original names of organisms are in Latin or Greek. And these ancient languages are dead now as a result of which, the form and spelling of the name cannot be modified.

The Microorganism are named by either of following sources:

  1. Description – The microorganism are named based on the description of their morphology like shape, size, and appearance. Ex. Staphylococcus aureus (staphylococcus means grape-like cluster of spheres and aureus means golden in color).
  1. Scientist’s names – The microorganism are named for the author who has isolated and identified it. Escherichia coli (The Escherichia name is from Theodor Esherich)
  1. Geographic places – The microorganism are also named from the geographical region they were first found. Pseudomonas fairmontensis (Fairmount Park is a place from, Pennsylvania, USA),
  1. Organization – The microorganisms are also named from the name of organization or institutes who have isolated or identified it. Afipia felis (the abrviation from Armed Forces Institute of Pathology, USA).


Activity for understanding Nomenclature and Classification:

Write the taxonomic classification of following microorganisms –

 Bacillus anthracisActinobacillus rossiClostridium septicum
Story of it’s name   
 Helicobacter canisProteus vulgarisRickettsia rickettsii
Story of it’s name   

Need more help? Click here.

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