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Veterinary bacteriology: information about important bacteria
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Nomenclature of bacteria


Nomenclature of bacteria refers to naming and bacteria and other organisms are named according to the binomial system, which was introduced by Carl Linnaeus (1674-1748). This means that a bacterium has a species name, which is composed of a genus name that tells you to which genus it belongs and a species epithet which, together with the genus name, is unique to the bacterium. An example of this is Moraxella bovis, where the genus name indicates that the bacterium belongs to the genus Moraxella and the species epithet indicates that the bacterium has been isolated from cattle. The genus name and the species epithet form together the scientific name of the species, which is always written in italics. Bacterial names are international and Latin or latinized Greek are used to form the name. If misunderstandings cannot occur, you can abbreviate the genus name after it has been written for the first time in a text, e.g. M. bovis. However, note that there are also bacteria called Mycoplasmopsis bovis and Mycobacterium bovis.

There are strict international rules for how bacteria should be named and these rules are published in a book named: "International Code of Nomenclature of Prokaryotes". In order to get a proposed name accepted, a scientific paper on the proposed species must be published and approved by an international taxonomy committee.

Trivial name

Trivial names are often used as a simplified way of naming a bacterial genus. A trivial name should neiter be written with capital first letter nor in italic. Examples of trivial names are: lactobacilli, mycobacteria, salmonella, staphylococci and streptococci. The scientific names for these groups are: genus Lactobacillus (or Lactobacillus spp.), genus Mycobacterium (or Mycobacterium spp.), genus Salmonella (or Salmonella spp.), genus Staphylococcus (or Staphylococcus spp.), genus Streptococcus (or Streptococcus spp.), respectively.

If you refer to a specific bacterial species, a trivial name refering to a complete genus should never be used.

Subspecies, biovars and serovars

Sometimes there is a need to divide bacterial species into subspecies, because they are too closely related to be regarded as different species, but too distantly related to be regarded as the same species. In this case a subspecies is introduced by adding a subspecies epithet and write subspecies (subsp. or ssp.) in front of it. An example of this is Streptococcus equi subsp. equi. When you divide a species into several subspecies, the original species always gets the same subspecies epithet as the species epithet.

There is often a need to divide species and subspecies in different biovars (bio­logi­cal variants) or different strains, but this is not strictly regulated, which means that researchers themselves can name their strains or biovars. One type of biovar is serovar (serological variant), by which various surface antigens can be identified with specific antibodies. Contact tracing and epidemiology is based on identification of different variants of the same bacterial species.

Serovar vs. serotype

Serovar and serotype are  synonyms and thus, interchangeable terms, but according to the Rules of the Bacteriological Code (1990 Revision), serovar is the preferred term. Serogroup is a group of bacteria containing a common antigen. A serogroup may contain several serotypes. Serogroup is not an official designation, but has been used to classify bacteria belonging to the genera Leptospira, Salmonella, Shigella and Streptococcus.

Salmonella nomenclature

A bacterial subspecies that occurs in several thousand different serovars is Salmonella enterica subsp. enterica. A common serovar is Dublin and if you you want to write the complete and correct name of the bacterium, it becomes Salmonella enterica subsp. enterica serovar Dublin. Please note that the name of the sero­var is capitalized, but not italicized. If the name appears in several places in the text, you can write S. enterica subsp. enterica serovar Dublin. However, because even this abbreviated writing is rather lengthy, it has been agreed that it is acceptable to simply write Salmonella Dublin, except on the first occurrance in a text, where the name must be given in full.

You can read more about naming of salmonellas on VetBact at Salmonella spp. and Salmonella enterica.

Updated: 2023-09-27.

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